Ben Murdin

Professor Ben Murdin


Professor of Physics, Head of the Photonics and Quantum Sciences Group
BA (Cantab), MSc (Heriot-Watt), PhD (Heriot-Watt)PA
+44 (0)1483 689328
15 ATI 01
Mrs Nicole Steward
01483689859

Biography

University roles and responsibilities

  • I am the Chair of the Department's Equality, Diversity and Inclusion Committee
  • I am the Group Leader for Photonics and Quantum Sciences

    My qualifications

    1993
    PhD, on mid and far-infrared spectroscopy of semiconductors
    Supervisor Prof Carl Pidgeon
    Heriot-Watt University

    Previous roles

    2005 - 2007
    School Director of Research (School of Physical Sciences)
    University of Surrey
    2007 - 2011
    Associate Dean (Research and Innovation), Faculty of Engineering and Physical Sciences
    University of Surrey

    Affiliations and memberships

    FInstP
    Fellow of the Institute of Physics

    Research

    Research interests

    Research collaborations

    My teaching

    Courses I teach on

    Postgraduate taught

    Undergraduate

    My publications

    Publications

    W Wu, P Greenland, A Fisher, HUY NGUYEN LE, Steven Chick, BENEDICT NEIL MURDIN (2018)Excited states of defect linear arrays in silicon: A first-principles study based on hydrogen cluster analogues, In: Physical Review B97(3)035205 The American Physical Society
    Excited states of a single donor in bulk silicon have previously been studied extensively based on effective mass theory. However, proper theoretical descriptions of the excited states of a donor cluster are still scarce. Here we study the excitations of lines of defects within a single-valley spherical band approximation, thus mapping the problem to a scaled hydrogen atom array. A series of detailed full configuration-interaction, time-dependent Hartree-Fock and time-dependent hybrid density-functional theory calculations have been performed to understand linear clusters of up to 10 donors. Our studies illustrate the generic features of their excited states, addressing the competition between formation of inter-donor ionic states and intra-donor atomic excited states. At short interdonor distances, excited states of donor molecules are dominant, at intermediate distances ionic states play an important role, and at long distances the intra-donor excitations are predominant as expected. The calculations presented here emphasise the importance of correlations between donor electrons, and are thus complementary to other recent approaches that include effective mass anisotropy and multi-valley effects. The exchange splittings between relevant excited states have also been estimated for a donor pair and for three-donor arrays; the splittings are much larger than those in the ground state in the range of donor separations between 10 and 20 nm. This establishes a solid theoretical basis for the use of excited-state exchange interactions for controllable quantum gate operations in silicon.
    JUERONG LI, HUY NGUYEN LE, KONSTANTIN LITVINENKO, STEVEN K CLOWES, H. Engelkamp, S. G. Pavlov, H. -W. . Hübers, V. B. Shuman, L. M. Portsel, A. N. Lodygin, A. Astrov, N. V. Abrosimov, C. R. Pidgeon, A. Fisher, Zaiping Zeng, Y. -M. Niquet, BENEDICT NEIL MURDIN (2018)Radii of Rydberg states of isolated silicon donors, In: Physical Review B98085423 American Physical Society
    We have performed a high field magneto-absorption spectroscopy on silicon doped with a variety of single and double donor species. The magnetic field provides access to an experimental magnetic length, and the quadratic Zeeman effect in particular may~be used to extract the wavefunction radius without reliance on previously determined effective mass parameters. We were therefore able to determine the limits of validity for the standard one-band anisotropic effective mass model. We also provide improved parameters and use them for an independent check on the accuracy of effective mass theory. Finally, we show that the optically accessible excited state wavefunctions have the attractive property that interactions with neighbours are far more forgiving of position errors than (say) the ground state.
    M van Loon, Nikolaos Stavrias, HUY NGUYEN LE, Konstantin Litvinenko, P Greenland, C Pidgeon, K Saeedi, B Redlich, G Aeppli, Benedict Murdin (2018)Giant multiphoton absorption for THz resonances in silicon hydrogenic donors, In: Nature Photonics12pp. 179-184 Nature Publishing Group
    The absorption of multiple photons when there is no resonant intermediate state is a well-known nonlinear process in atomic vapours, dyes and semiconductors. The N-photon absorption (NPA) rate for donors in semiconductors scales proportionally from hydrogenic atoms in vacuum with the dielectric constant and inversely with the effective mass, factors that carry exponents 6N and 4N, respectively, suggesting that extremely large enhancements are possible. We observed 1PA, 2PA and 3PA in Si:P with a terahertz free-electron laser. The 2PA coefficient for 1s–2s at 4.25 THz was 400,000,000 GM (=4 × 10−42 cm4 s), many orders of magnitude larger than is available in other systems. Such high cross-sections allow us to enter a regime where the NPA cross-section exceeds that of 1PA—that is, when the intensity approaches the binding energy per Bohr radius squared divided by the uncertainty time (only 3.84 MW cm−2 in silicon)—and will enable new kinds of terahertz quantum control.
    H. Le Nguyen, Grigory V. Lanskii, G. Aeppli Aeppli, BENEDICT NEIL MURDIN (2019)Giant non-linear susceptibility of hydrogenic donors in silicon and germanium, In: Light: Science & Applications864pp. 1-7 Springer Nature
    Implicit summation is a technique for conversion of sums over intermediate states in multiphoton absorption and the high-order susceptibility in hydrogen into simple integrals. Here we derive the equivalent technique for hydrogenic impurities in multi-valley semiconductors. While the absorption has useful applications it is primarily a loss process, conversely the non-linear susceptibility is a crucial parameter for active photonic devices. For Si:P we predict the hyperpolarizability ranges from X(3)n3D = 2:9 to 580x10-38m5V2 depending on the frequency even while avoiding resonance. Using samples of reasonable density n3D and thickness L to produce third harmonic generation at 9 THz, a frequency that is difficult to produce with existing solid state sources, we predict that X(3) should exceed that of bulk InSb and X(3)L should exceed that of graphene and resonantly enhanced quantum wells.
    T. Peach, K. Stockbridge, Juerong Li, K. P. Homewood, M. A. Lourenco, S. Chick, M. A. Hughes, B. N. Murdin, S. K. Clowes (2019)Enhanced diffusion and bound exciton interactions of high density implanted bismuth donors in silicon, In: Applied Physics Letters115(7)072102pp. 1-8 AIP Publishing
    This study reports the effect of an increasing ion dose on both the electrical activation yield and the characteristic properties of implanted bismuth donors in silicon. A strong dependence of implant fluence is observed on both the yield of bismuth donors and the measured impurity diffusion. This is such that higher ion concentrations result in both a decrease in activation and an enhancement in donor migration through interactions with mobile silicon lattice vacancies and interstitials. Furthermore, the effect of implant fluence on the properties of the Si:Bi donor bound exciton, D0X, is also explored using photoluminescence (PL) measurements. In the highest density sample, centers corresponding to the PL of bismuth D0Xs within both the high density region and the lower concentration diffused tail of the implanted donor profile are identifiable.
    I. P. Marko, A. R. Adams, S. J. Sweeney, S. R. Jin, B. N. Murdin, R. Schwertberger, A. Somers, J. P. Reithmaier, A. Forchel (2004)Experimental investigations into the thermal properties of 1.5-1.8-/spl mu/m InAs/InP quantum dash laserspp. 61-62

    We present what we believe to be the first ever high-pressure and spontaneous emission measurements on quantum dash lasers. The results show that temperature sensitivity of these lasers is caused by nonradiative processes, which depend on the lasing wavelength.

    I P Marko, A R Adams, S J Sweeney, S R Jin, B N Murdin, R Schwertberger, A Somers, J P Reithmaier, A Forchel (2004)Experimental Investigations into the Thermal Properties of 1.5-1.8μm InAs/InP Quantum Dash Lasers, In: 2004 IEEE 19th International Semiconductor Laser Conference, 2004. Conference Digest.

    We present what we believe to be the first ever high-pressure and spontaneous emission measurements on quantum dash lasers. The results show that temperature sensitivity of these lasers is caused by nonradiative processes, which depend on the lasing wavelength.

    S. R. Jin, C. N. Ahmad, S. J. Sweeney, A. R. Adams, B. N. Murdin, H. Page, X. Marcadet, C. Sirtori, S. Tomić (2006)Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, In: Applied Physics Letters221105(2006)

    We report on the pressure dependence of the threshold current in 1.3 mum InGaAsP and 1.5 mum InGaAs quantum-well lasers measured at low temperatures similar to100 K. It was found that the threshold current of both devices slowly increases with increasing pressure (i.e., increasing band gap) at similar to100 K consistent with the calculated variation of the radiative current. In contrast, at room temperature we observed a reduction of the threshold current with increasing pressure. Our low-temperature, high-pressure data confirm the results of previous atmospheric pressure measurements on the same devices which indicated a transition in the dominant recombination mechanism from radiative to Auger as the device temperature is increased from similar to100 to 300 K.

    B. N. Murdin, A. R. Adams, P. Murzyn, C. R. Pidgeon, I. V. Bradley, J-P. R. Wells, Y. H. Matsuda, N. Miura, T. Burke, A. D. Johnson (2002)Band anticrossing in dilute InNxSb1–x, In: Applied Physics Letters256(2002)

    Dilute nitrogen alloys of InSb exhibit extremely strong band gap bowing with nitrogen composition that has been associated with anticrossing between the localized resonant states of the nitrogen within the conduction band and the extended states of the conduction band itself. This also results in the conduction band dispersion having an enhanced nonparabolicity. We have measured the electron effective mass near the anticrossing by cyclotron resonance in InNxSb1–x alloys with absorption edge near 15 µm, using pulsed fields up to 150 T. The results directly demonstrate the band anticrossing and quantitatively confirm the increase of effective mass versus x predicted for InNxSb1–x by a tight binding calculation for low nitrogen concentration (x<0.01).

    S. R. Jin, S. J. Sweeney, C. N. Ahmad, A. R. Adams, B. N. Murdin (2004)Radiative and Auger recombination in 1.3 µm InGaAsP and 1.5 µm InGaAs quantum-well lasers measured under high pressure at low and room temperatures, In: Applied Physics Letters357(2004)

    We report on the pressure dependence of the threshold current in 1.3 µm InGaAsP and 1.5 µm InGaAs quantum-well lasers measured at low temperatures ~100 K. It was found that the threshold current of both devices slowly increases with increasing pressure (i.e., increasing band gap) at ~100 K consistent with the calculated variation of the radiative current. In contrast, at room temperature we observed a reduction of the threshold current with increasing pressure. Our low-temperature, high-pressure data confirm the results of previous atmospheric pressure measurements on the same devices which indicated a transition in the dominant recombination mechanism from radiative to Auger as the device temperature is increased from ~100 to 300 K

    S. A. Choulis, A. Andreev, M. Merrick, A. R. Adams, B. N. Murdin, A. Krier, V. V. Sherstnev (2003)High-pressure measurements of mid-infrared electroluminescence from InAs light-emitting diodes at 3.3 µm, In: Applied Physics Letters1149(2003)

    The spontaneous electroluminescence emission of InAs light-emitting diodes (LEDs) operating at 3.3 µm was studied as a function of applied hydrostatic pressure. An enhancement of a factor of almost four in radiative efficiency at room temperature was observed in the range 0 to 10 kbar. Analysis of the dependence of electroluminescence emission intensity on hydrostatic pressure at constant current reveals that nonradiative Auger recombination dominates the quantum efficiency of these LEDs.

    B. N. Murdin, M. Kamal-Saadi, A. Lindsay, E. P. O'Reilly, A. R. Adams, G. J. Nott, J. G. Crowder, C. R. Pidgeon, I. V. Bradley, J-P. R. Wells, T. Burke, A. D. Johnson, T. Ashley (2001)Auger recombination in long-wavelength infrared InNxSb1–x alloys, In: Applied Physics Letters1568(2001)

    Dilute nitrogen alloys of InSb exhibit strong band gap bowing with increasing nitrogen composition, shifting the absorption edge to longer wavelengths. The conduction band dispersion also has an enhanced nonparabolicity, which suppresses Auger recombination. We have measured Auger lifetimes in alloys with 11 and 15 µm absorption edges using a time-resolved pump-probe technique. We find the lifetimes to be longer at room temperature than equivalent band gap Hg1–yCdyTe alloys at the same quasi-Fermi level separation. The results are explained using a modified k·p Hamiltonian which explicitly includes interactions between the conduction band and a higher lying nitrogen-related resonant band.

    K. O'Brien, S. J. Sweeney, A. R. Adams, B. N Murdin, A. Salhi, Y. Rouillard, A. Joullié (2006)Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 µm, In: Applied Physics Letters051104(2006)

    The temperature dependence of the threshold current of InGaAsSb/AlGaAsSb compressively strained lasers is investigated by analyzing the spontaneous emission from working laser devices through a window formed in the substrate metallization and by applying high pressures. It is found that nonradiative recombination accounts for 80% of the threshold current at room temperature and is responsible for the high temperature sensitivity. The authors suggest that Auger recombination involving hot holes is suppressed in these devices because the spin-orbit splitting energy is larger than the band gap, but other Auger processes persist and are responsible for the low T0 values.

    S A Choulis, A Andreev, M Merrick, A R Adams, B N Murdin, A Krier, V V Sherstnev (2003)High-Pressure Measurements of Mid-Infrared Electroluminescence from InAs Light-Emitting Diodes at 3.3μm, In: Applied Physics Letters82(8)pp. 1149-1151

    The spontaneous electroluminescence emission of InAs light-emitting diodes (LEDs) operating at 3.3 μm was studied as a function of applied hydrostatic pressure. An enhancement of a factor of almost four in radiative efficiency at room temperature was observed in the range 0 to 10 kbar. Analysis of the dependence of electroluminescence emission intensity on hydrostatic pressure at constant current reveals that nonradiative Auger recombination dominates the quantum efficiency of these LEDs

    K O'Brien, S J Sweeney, A R Adams, B N Murdin, A Salhi, Y Rouillard, A Joullie (2006)Recombination Processes in Midinfrared InGaAsSb Diode Lasers Emitting at 2.37 mu m, In: Applied Physics Letters89(5)

    The temperature dependence of the threshold current of InGaAsSb/AlGaAsSb compressively strained lasers is investigated by analyzing the spontaneous emission from working laser devices through a window formed in the substrate metallization and by applying high pressures. It is found that nonradiative recombination accounts for 80% of the threshold current at room temperature and is responsible for the high temperature sensitivity. The authors suggest that Auger recombination involving hot holes is suppressed in these devices because the spin-orbit splitting energy is larger than the band gap, but other Auger processes persist and are responsible for the low T-0 values.

    S R Jin, C N Ahmad, S J Sweeney, A R Adams, B N Murdin, H Page, X Marcadet, C Sirtori, S Tomic (2006)Spectroscopy of GaAs/AlGaAs Quantum-Cascade Lasers Using Hydrostatic Pressure, In: Applied Physics Letters89(22)

    The authors have measured the output spectrum and the threshold current in 9.2 mu m wavelength GaAs/Al0.45Ga0.55As quantum-cascade lasers at 115 K as a function of hydrostatic pressure up to 7.3 kbars. By extrapolation back to ambient pressure, thermally activated escape of electrons from the upper lasing state up to delocalized states of the Gamma valley is shown to be an important contribution to the threshold current. On the other hand leakage into the X valley, although it has a very high density of states and is nearly degenerate with the Gamma band edge in the barrier, is insignificant at ambient pressure.

    Gemma R. Chapman (2020)Integration of Microwaves for Solotronic Applications University of Surrey
    Solotronic devices formed from group V dopants in silicon are a prospective option as a qubit system for quantum technologies. A spin-based silicon based quantum computer is highly promising with the longest qubit coherence times found to date, and an existing compatibility with the CMOS industry. The electron spin states of silicon solotronic devices are controlled through resonance absorption of microwave frequencies. Due to the small dimensions of the dopants, integration of the microwaves to ensure individual qubit addressability is a important step on the path to producing a commercial quantum computer. Within this thesis, we investigate two different pathways to potentially optimise this process. Mesoscopic interconnects could be used to deliver microwaves to individual qubits within a qubit array. Conventional metals are not suitable as the resistivity increases as the dimensions approach the atomic scale and have immature nanoscale fabrication techniques. Highly doped metallic phosphorous delta-doped monolayers in silicon could be a viable material for mesoscopic transmission lines. Si:P delta-doped nanowires can be fabricated with atomic precision and have been shown to maintain ohmic behaviour down to wire widths of 1.5nm. The microwave characterisation of Si:P delta-doped layers was completed validating that it is a suitable material for microwave propagation. The transmission parameters are extracted and matched to a circuit model and complementary electromagnetic simulations. A universal nanoscale transmission model showed that Si:P nanowires have transmission parameters equivalent to graphene nanoribbons and have optimal behaviour compared to copper nanowires below 5nm. This investigation has further reaching applications than silicon quantum technologies as conventional microelectronics also require mesoscopic interconnects as Moore's law progresses. The application of an external magnetic field modulates the electron spin splitting within a group V donor and has a linear relationship with the resonant microwave frequency under high magnetic fields. Within the literature, external magnetic fields approaching 10T are being used to optimise the operating conditions of the qubit and to simplify the experimental parameters. Knowledge of the behaviour and mechanisms of the spin lattice relaxation is unknown at these fields. Electron spin resonance in phosphorous doped silicon was demonstrated at magnetic fields between 10-14T using electrically detected donor bound exciton spectroscopy. To accompany this investigation, the first donor bound exciton spectroscopy model under the influence of magnetic field was developed and analysed.
    The advances in semiconductor technology coupled with the potential of lab-on-chip spectroscopy, long wavelength telecommunications and small-scale optical interconnects has invigorated academic and commercial interest in mid-infrared optoelectronics. However, significant challenges remain. This thesis explores two approaches for mid-infrared optoelectronic lasers. Type-I GaSb quantum well lasers exhibit some of the highest performance metrics of any semiconductor laser system in the 2 μm – 3 μm wavelength range. However, the threshold current density increases substantially with increasing wavelength and temperature, impacting component reliability and the overall efficiency of a laser-based optoelectronic system. Through a combination of temperature and hydrostatic pressure techniques, Auger recombination is identified as the dominant cause for the performance degradation of type-I mid-infrared laser with increasing wavelength and temperature. Using hydrostatic pressure measurements, the wavelength dependence of the Auger coefficient over the 2 μm - 3 μm range is constructed, revealing two important regimes. At wavelengths < 2 μm the CHSH Auger process dominates the room temperature non-radiative threshold current. For wavelength > 2 μm, the CHSH process is effectively suppressed due to the energetic separation between the lasing energy and the spin-orbit split-off band. In this regime another Auger process, such as CHCC or CHLH recombination begins to dominate, increasing exponentially with wavelength. The temperature dependence of the radiative and non-radiative threshold current density indicates that this Auger process has an activated character and is sensitive to the intrinsic properties of the quantum well band structure. To leverage the advanced manufacturing capabilities and high yields of the Si-microelectronics industry, there is intense research activity to realise CMOS compatible optoelectronics. One emerging strategy is to augment the optical properties of group-IV materials through band structure engineering, such as incorporating Sn into the Ge lattice. Hydrostatic pressure measurements of the GeSn absorption edge exhibit an intermediate pressure coefficient between that of the Γ and L conduction band critical points. This is indicative of strong band mixing effects in the GeSn alloy. In the presence of band mixing the conventional distinction between the indirect and direct band gap breaks down. Instead it is more appropriate to discuss the nature of the band gap in terms of the fractional Γ-character of the conduction band states at the band edge. The pressure coefficient of the absorption edge for samples with Sn content between 6% – 10% reveal a continuous evolution in the Γ-character with increasing Sn-concentration. High Γ-character is observed even at low Sn concentrations of 6%, when the GeSn alloy is expected to exhibit a fundamentally indirect band gap. These band mixing effects have important implications for designing efficient photonic and electronic devices utilizing GeSn and related material systems.
    This thesis is concerned with the generation of terahertz (THz) light in the frequency range of 5–15 THz. This range is difficult to produce at high intensities, and no high-power table-top sources exist for it. The reasons for the interest in this frequency range are broad, and include communications, chemical and biomedical spectroscopy, etc. Different applications require highly specific technological characteristics, such as room temperature operation or very high stability, and satisfying all possible requirements in one generation mechanism is difficult. In this study, we sought to develop a solution to the problem of optical pumping of donor impurities in silicon, to control the orbit and spin of the donor electron in quantum computer gates. It is obvious that great advantages would be obtained if this control were possible with a bench-top source, and this is the key to enabling such high efficiency control to spread to the wider community of physicists and engineers working on spin qubits. To achieve this purpose, we explore the possibility of use a cheap material like single doped silicon and germanium to triple THz radiation from 1.7 to 5 THz (which is available from Quantum Cascade Laser diodes). The presence of the dopants modifies substantially the optical properties of the semiconductors, generating large nonlinear coefficients at THz frequencies. Samples of bismuth doped silicon and phosphorus, arsenic and antimony doped germanium has been characterised using frequency-domain and time-domain spectroscopy, and finally the optical nonlinear coefficient of Si:Bi has been measure by a Four Wave Mixing (FWM) experiment. We have found that the nonlinear susceptibility $____chi^{(3)}$ of Si:Bi at resonance is the highest ever reported for a bulk material.
    Konstantin Litvinenko, PT Greenland, B Redlich, CR Pidgeon, G Aeppli, Benedict Murdin (2016)Weak probe readout of coherent impurity orbital superpositions in silicon, In: Physical Review B - Condensed Matter and Materials Physics94(23)235207 American Physical Society
    Pump-probe spectroscopy is the most common time-resolved technique for investigation of electronic dynamics, and the results provide the incoherent population decay time T1. Here we use a modified pump-probe experiment to investigate coherent dynamics, and we demonstrate this with a measurement of the inhomogeneous dephasing time T2* for phosphorus impurities in silicon. The pulse sequence produces the same information as previous coherent all-optical (photon-echo-based) techniques but is simpler. The probe signal strength is first order in pulse area but its effect on the target state is only second order, meaning that it does not demolish the quantum information. We propose simple extensions to the technique to measure the homogeneous dephasing time T2, or to perform tomography of the target qubit.
    PT Greenland, SA Lynch, AFG van der Meer, BN Murdin, CR Pidgeon, B Redlich, NQ Vinh, G Aeppli (2010)Coherent control of Rydberg states in silicon, In: NATURE465(7301)pp. 1057-1061 NATURE PUBLISHING GROUP
    Laser cooling and electromagnetic traps have led to a revolution in atomic physics, yielding dramatic discoveries ranging from Bose-Einstein condensation to the quantum control of single atoms(1). Of particular interest, because they can be used in the quantum control of one atom by another, are excited Rydberg states(2-4), where wavefunctions are expanded from their ground-state extents of less than 0.1 nm to several nanometres and even beyond; this allows atoms far enough apart to be non-interacting in their ground states to strongly interact in their excited states. For eventual application of such states(5), a solid-state implementation is very desirable. Here we demonstrate the coherent control of impurity wavefunctions in the most ubiquitous donor in a semiconductor, namely phosphorus-doped silicon. In our experiments, we use a free-electron laser to stimulate and observe photon echoes(6,7), the orbital analogue of the Hahn spin echo(8), and Rabi oscillations familiar from magnetic resonance spectroscopy. As well as extending atomic physicists' explorations(1-3,9) of quantum phenomena to the solid state, our work adds coherent terahertz radiation, as a particularly precise regulator of orbitals in solids, to the list of controls, such as pressure and chemical composition, already familiar to materials scientists(10).
    Michael R George, Paul E Critchley, George F.S Whitehead, Andrew J Bailey, Francesco Cuda, Benedict N Murdin, Martin C Grossel, Richard J Curry (2021)Modified pyridine-2,6-dicarboxylate acid ligands for sensitization of near-infrared luminescence from lanthanide ions (Ln3+ = Pr3+, Nd3+, Gd3+, Dy3+, Er3+), In: Journal of luminescence230117715 Elsevier B.V
    A detailed study of the ability of pyridine-2,6-dicarboxylic acid (1) and its 4-mono- and 3,4,5-tri-substituted analogues to sensitize emission from Pr3+, Nd3+, Gd3+, Dy3+ and Er3+ is presented. Sensitization of Ln3+ emission was demonstrated via the ligands in all complexes, excluding Gd3+, with emission covering the spectral range from 500 nm to 1850 nm obtained with variation of the Ln3+ ion. From the study of the ligand-based photoluminescence obtained from Gd3+-complexes, and the relative ligand and Ln3+ emission obtained from the other complexes, the singlet and triplet state energies of complexes of (1) are estimated to be at 3.1 eV and 2.6 eV respectively whilst for the 3,5-dibromo-substituted complexes (4) they are at 2.9 eV and 2.3 eV. Hypersensitivity of the Er3+4I15/2 → 2H11/2 and 4I15/2 → 4G11/2 intra-atomic transitions is also observed in the 4-chloro-substituted (3) complex. Enhanced sensitization of Nd3+ (ca. 5-fold) and Er3+ (ca. 2-fold) near-infrared emission is demonstrated for complexes of (3) and (4) respectively in comparison with those of (1). •Sensitized luminescence from dipicolinate lanthanide complexes from 500 to 1850 nm.•Enhanced sensitization of near infrared emission from Nd3+ and Er3+ complexes.•Hypersensitivity of Er3+ intra-atomic transitions observed.•Study of ligand-state interactions with Pr3+, Nd3+, Gd3+, Dy3+ and Er3+ ions.
    K. L. Litvinenko, L. Nikzad, J. Allam, B. N. Murdin, C. R. Pidgeon, J. J. Harris, T. Zhang, L. F. Cohen (2007)Spin lifetime in high quality InSb epitaxial layers grown on GaAs, In: Journal of Applied Physics083105(2007)

    The spin relaxation in undoped InSb films grown on GaAs has been investigated in the temperature range from 77 to 290 K. Two distinct lifetime values have been extracted, 1 and 2.5 ps, dependent on film thickness. Comparison of this data with a multilayer transport analysis of the films suggests that the longer time (~2.5 ps at 290 K) is associated with the central intrinsic region of the film, while the shorter time (~1 ps) is related to the highly dislocated accumulation region at the film-substrate interface. Whereas previous work on InAs films grown on GaAs showed that the native surface defect resulted in an additional charge accumulation layer with high conductivity but very short spin lifetime, in InSb layers the surface states introduce a depletion region. We infer that InSb could be a more attractive candidate for spintronic applications than InAs.

    Steven Chick, B N Murdin, Guy Matmon, Mira Naftaly (2018)Metrology of complex refractive index for solids in the terahertz regime using frequency domain spectroscopy, In: Metrologia55(6)pp. 771-781
    Frequency domain spectroscopy allows an experimenter to establish optical properties of solids in a wide frequency band including the technically challenging 3-10 THz region, and in other bands enables metrological comparison between competing techniques. We advance a method for extracting the optical properties of high-index solids using only transmission-mode frequency domain spectroscopy of plane-parallel Fabry-Perot optical flats. We show that different data processing techniques yield different kinds of systematic error, and that some commonly used techniques have inherent systematic errors which are underappreciated. We use model datasets to cross-compare algorithms in isolation from experimental errors, and propose a new algorithm which has qualitatively different systematic errors to its competitors. We show that our proposal is more robust to experimental non-idealities such as noise or apodization, and extract the complex refractive index spectrum of crystalline silicon as a practical example. Finally, we advance the idea that algorithms are complementary rather than competitive, and should be used as part of a toolbox for better metrology.
    B N Murdin, K Litvinenko, J Allam, C R Pidgeon, M Bird, K Morrison, T Zhang, S K Clowes, W R Branford, J Harris, L F Cohen (2005)Temperature and Doping Dependence of Spin Relaxation in n-InAs, In: Physical Review B72(8)

    We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in the narrow gap semiconductor material n-InAs as a function of temperature, doping, and pump wavelength. The results are consistent with the D'Yakonov-Perel mechanism for temperatures between 77 and 300 K. However, the data suggest that electron-electron scattering should be taken into account in determining the dependence of the spin lifetime on the carrier concentration in the range 5.2x10(16)-8.8x10(17) cm(-3). For a sample with doping of 1.22x10(17) cm(-3) the spin lifetime was 24 ps at room temperature. By applying a magnetic field in the sample plane we also observed coherent precession of the spins in the time domain, with a g factor g(*)=-13, also at room temperature.

    B Wittmann, LE Golub, SN Danilov, J Karch, C Reitmaier, ZD Kvon, NQ Vinh, AFG van der Meer, B Murdin, SD Ganichev (2008)Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions, In: PHYSICAL REVIEW B78(20)ARTN 2pp. ?-? AMER PHYSICAL SOC
    P. Murzyn, C. R. Pidgeon, P. J. Phillips, M. Merrick, K. L. Litvinenko, J. Allam, B. N. Murdin, T. Ashley, J. H. Jefferson, A. Miller, L. F. Cohen (2005)Erratum: "Suppression of D'yakonov-Perel spin relaxation in InAs and InSb by n-type doping at 300 K" [Appl. Phys. Lett. 83, 5220 (2003)], In: Applied Physics Letters129901(2005)
    G Matmon, Eran Ginossar, B Villis, A Kolker, T Lim, H Solanki, S Schofield, N Curson, Juerong Li, Benedict Murdin, A Fisher, G Aeppli (2018)2D-3D crossover in a dense electron liquid in silicon, In: Physical Review B97155306 American Physical Society
    Doping of silicon via phosphine exposures alternating with molecular beam epitaxy overgrowth is a path to Si:P substrates for conventional microelectronics and quantum information technologies. The technique also provides a new and well-controlled material for systematic studies of two-dimensional lattices with a half-filled band. We show here that for a dense (ns = 2.8 × 1014 cm−2 ) disordered two-dimensional array of P atoms, the full field angle-dependent magnetostransport is remarkably well described by classic weak localization theory with no corrections due to interaction effects. The two- to three-dimensional cross-over seen upon warming can also be interpreted using scaling concepts, developed for anistropic three-dimensional materials, which work remarkably except when the applied fields are nearly parallel to the conducting planes.
    C. R. Pidgeon, J.-P. R. Wells, I. V. Bradley, B. N. Murdin (2000)Double resonance and four wave mixing FEL studies of InAs/GaAs quantum dots and local modes in ionic crystals, In: 25th International Conference on Infrared and Millimeter Waves (Cat. No.00EX442)pp. 163-164

    A brief review is given of lifetime and line broadening studies with the free electron laser at FOM-Rijnhuizen (FELIX), emphasising work on far infrared (FIR) modulated photoluminescence (PL) of bound-to-bound transitions in InAs/GaAs quantum dots and mid-infrared (MIR) four wave mixing experiments on localised modes of H- ions in calcium fluoride crystals. We have made new far/near infrared double resonance measurements of self-assembled InAs/GaAs quantum dots. The FIR resonance is unambiguously associated with a bound-bound intraband transition in the neutral dots, and analysis of the FIR double resonance linewidth enables us to show that the inhomogeneous broadening of the PL cannot be attributed solely to size and composition fluctuation. In addition we have made time resolved studies of local modes in ionic crystals, where nonradiative decay plays an important role in the optical pumping cycle of laser gain media. We have made pump-probe studies of the local modes created upon the introduction of a light impurity, in particular the H - ion, in CaF2 in the spectral region 700 to 1200 cm-1. We have also measured the free induction decay of this mode using a noncollinear degenerate four wave mixing geometry. The observed coherent transient is striking in having large quantum beat modulations at negative time which are associated with vibrational ladder climbing.

    J. Roither, S. Pichler, M. V. Kovalenko, W. Heiss, P. Feychuk, O. Panchuk, J. Allam, B. N. Murdin (2006)Two- and one-dimensional light propagations and gain in layer-by-layer-deposited colloidal nanocrystal waveguides, In: Applied Physics Letters111120(2006)

    Optical waveguides containing high percentages of colloidal nanocrystals have been fabricated by layer-by-layer deposition on planar and patterned glass substrates. The two- and one-dimensional waveguidings in these structures are demonstrated by propagation loss experiments. The experimental results obtained for various film thicknesses and widths of the waveguide stripes together with simulations of the light propagation indicate that the losses are dominated by surface roughness. The variable stripe length method is used to determine the optical gain of 230 cm–1 from the amplified spontaneous emission. This high value makes the authors' waveguide structures very promising for applications in amplifiers and lasers with reduced threshold powers.

    A M Gilbertson, M Fearn, J H Jefferson, B N Murdin, P D Buckle, L F Cohen (2008)Zero-Field Spin Splitting and Spin Lifetime in n-InSb/In1-xAlxSb Asymmetric Quantum Well Heterostructures, In: Physical Review B77(16)

    The spin-orbit (SO) coupling parameters for the lowest conduction subband due to structural inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) are calculated for a range of carrier densities in [001]-grown delta-doped n-type InSb/In1-xAlxSb quantum wells using the established eight-band k center dot p formalism [J. Deng , Phys. Rev. B 59, R5312 (1999)]. We present calculations for conditions of zero bias at 10 K. It is shown that both the SIA and BIA parameters scale approximately linearly with carrier density, and exhibit a marked dependence on well width when alloy composition is adjusted to allow maximum upper barrier height for a given well width. In contrast to other material systems, the BIA contribution to spin splitting is found to be of significant and comparable value to the SIA mechanism in these structures. We calculate the spin lifetime tau(s[1 (1) over bar0]) for spins oriented along [1 (1) over bar0] based on D'yakonov-Perel' mechanism using both the theory of Averkiev [J. Phys.: Condens. Matter 14, R271 (2002)] and also directly the rate of precession of spins about the effective magnetic field, taking into account all three SO couplings, which show good agreement. tau(s[1 (1) over bar0]) is largest in the narrowest wells over the range of moderate carrier densities considered, which is attributed to the reduced magnitude of the k-cubic BIA parameter in narrow wells. The inherently large BIA induced SO coupling in these systems is shown to have considerable effect on tau(s[1 (1) over bar0]), which exhibits significant reduction in the maximum spin lifetime compared to previous studies that consider systems with relatively weak BIA induced SO coupling. The relaxation rate of spins oriented in the [001] direction is found to be dominated by the k-linear SIA and BIA coupling parameters and at least an order of magnitude greater than in the [1 (1) over bar0] direction.

    Steven Chick, N. Stavrias, K. Saeedi, B. Redlich, P. T. Greenland, G. Matmon, M. Naftaly, C. R. Pidgeon, G. Aeppli, Benedict Murdin (2017)Coherent superpositions of three states for phosphorous donors in silicon prepared using THz radiation, In: Nature Communications816038 Nature Publishing Group
    Superposition of orbital eigenstates is crucial to quantum technology utilising atoms, such as atomic clocks and quantum computers, and control over the interaction between atoms and their neighbours is an essential ingredient for both gating and readout. The simplest coherent wavefunction control uses a 2-eigenstate admixture, but more control over the spatial distribution of the wavefunction can be obained by increasing the number of states in the wavepacket. Here we demonstrate THz laser pulse control of Si:P orbitals using multiple orbital state admixtures, observing beat patterns produced by Zeeman splitting. The beats are an observable signature of the ability to control the path of the electron, which implies we can now control the strength and duration of the interaction of the atom with different neighbours. This could simplify surface code networks which require spatially controlled interaction between atoms, and we propose an architecture that might take advantage of this.
    N Stavrias, K Saeedi, B Redlich, PT Greenland, H Riemann, NV Abrosimov, MLW Thewalt, CR Pidgeon, Benedict Murdin (2017)Competition between homogeneous and inhomogeneous broadening of orbital transitions in Si:Bi, In: Physical Review B96(15)155204 American Physical Society
    We present results for the lifetime of the orbital transitions of Bi donors in Si, measured using both frequency domain and time-domain techniques, allowing us to distinguish between homogeneous and inhomogeneous processes. The proximity of the energy of the optically allowed transitions to the optical phonon energy means that there is an unusually wide variation in the lifetimes and broadening mechanisms for this impurity, from fully homogeneous lifetime-broadened transitions to fully inhomogeneously broadened lines. The relaxation lifetime (T1) of the states range from the low 10’s to 100’s of ps, and we find that there is little extra dephasing (so that T1 is of the order of T2/2) in each case.
    K Litvinenko, M Leontiadou, J Li, E Bowyer, S Clowes, CR Pidgeon, B Murdin (2011)Manipulation of spin dynamics in semiconductor structures by orientation of small external magnetic field, In: AIP Conference Proceedings1399pp. 657-658
    Electron spin relaxation times have been measured in InSb and InAs quantum wells and epi-layers in a moderate (<4T) external magnetic field by means of time-resolved optical orientation using circularly polarised light. A strong and opposite field dependence of the spin lifetime was observed for longitudinal (Faraday) and transverse (Voigt) configuration. In the Faraday configuration the spin lifetime increases because the DP dephasing process is suppressed. At the high field limit the EY relaxation process dominates, enabling its direct determination. Conversely, in the Voigt configuration an additional efficient spin dephasing mechanism dominates and shortens the electron spin lifetime considerably with B-2. We demonstrate that for narrow gap semiconductors simply changing the direction of the magnetic field of 1T can alter the electron spin lifetime by one order of magnitude.
    SN Danilov, B Wittmann, P Olbrich, W Prettl, LE Golub, EV Beregulin, Z-D Kvon, NN Mikhailov, SA Dvoretsky, VA Shalygin, NQ Vinh, AFG van der Meer, B Murdin, SD Ganichev (2009)All Electrical Detection of the Stokes Parameters of IR/THz Radiation, In: 2009 34TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES, VOLS 1 AND 2pp. 298-299
    Konstantin Litvinenko, Juerong Li, N Stavrias, A Meaney, P Christianen, H Engelkamp, Kevin Homewood, C Pidgeon, Benedict Murdin (2016)The Quadratic Zeeman effect used for state-radius determination in neutral donors and donor bound excitons in Si:P, In: Semiconductor Science and Technology31045007pp. 045007-045007 IOP
    We have measured the near-infrared photoluminescence spectrum of phosphorus doped silicon (Si: P) and extracted the donor-bound exciton (D0X) energy at magnetic fields up to 28 T. At high field the Zeeman effect is strongly nonlinear because of the diamagnetic shift, also known as the quadratic Zeeman effect (QZE). The magnitude of the QZE is determined by the spatial extent of the wave-function. High field data allows us to extract values for the radius of the neutral donor (D0) ground state, and the light and heavy hole D0X states, all with more than an order of magnitude better precision than previous work. Good agreement was found between the experimental state radius and an effective mass model for D0. The D0X results are much more surprising, and the radius of the mJ=±3/2 heavy hole is found to be larger than that of the mJ=±1/2 light hole.
    H-W Huebers, SG Pavlov, SA Lynch, T Greenland, KL Litvinenko, B Murdin, B Redlich, AFG van der Meer, H Riemann, NV Abrosimov, P Becker, H-J Pohl, RK Zhukavin, VN Shastin (2013)Isotope effect on the lifetime of the 2p(0) state in phosphorus-doped silicon, In: PHYSICAL REVIEW B88(3)ARTN 0pp. ?-? AMER PHYSICAL SOC
    Kristian Stockbridge, Steven Chick, E. Crane, A. Fisher, Benedict Murdin Using non-homogeneous point process statistics to find multi-species event clusters in an implanted semiconductor, In: Journal of Physics Communications IOP Publishing
    The Poisson distribution of event-to-ith-nearest-event radial distances is well known for homogeneous processes that do not depend on location or time. Here we investigate the case of a non-homogeneous point process where the event probability (and hence the neighbour configuration) depends on location within the event space. The particular non-homogeneous scenario of interest to us is ion implantation into a semiconductor for the purposes of studying interactions between the implanted impurities. We calculate the probability of a simple cluster based on nearest neighbour distances, and specialise to a particular two-species cluster of interest for qubit gates. We show that if the two species are implanted at different depths there is a maximum in the cluster probability and an optimum density profile.
    J Roither, S Pichler, M V Kovalenko, W Heiss, P Feychuk, O Panchuck, J Allam, B N Murdin (2006)Two- and One-Dimensional Light Propagations and Gain in Layer-by-Layer-Deposited Colloidal Nanocrystal Waveguides, In: Applied Physics Letters89(11)

    Optical waveguides containing high percentages of colloidal nanocrystals have been fabricated by layer-by-layer deposition on planar and patterned glass substrates. The two- and one-dimensional waveguidings in these structures are demonstrated by propagation loss experiments. The experimental results obtained for various film thicknesses and widths of the waveguide stripes together with simulations of the light propagation indicate that the losses are dominated by surface roughness. The variable stripe length method is used to determine the optical gain of 230 cm(-1) from the amplified spontaneous emission. This high value makes the authors' waveguide structures very promising for applications in amplifiers and lasers with reduced threshold powers.

    I. Galbraith, R. Chari, S. Pellegrini, P. J. Phillips, C. J. Dent, A. F. G. van der Meer, D. G. Clarke, A. K. Kar, G. S. Buller, C. R. Pidgeon, B. N. Murdin, J. Allam, G. Strasser (2005)Excitonic signatures in the photoluminescence and terahertz absorption of a GaAs/AlxGa1–xAs multiple quantum well, In: Physical Review B71(073302)

    Measurements of the THz absorption and the time-resolved photoluminescence have been performed on the same GaAs quantum well sample. The strength of the absorption at the internal 1s-2p exciton transition frequency is used as a measure of the density of excitons in the sample. When the interband pump laser is resonant with the 1s exciton frequency, induced absorption at the s-2p frequency is clearly seen. If the same density of carriers is created pumping in the continuum, no significant 1s-2p absorption is seen in a time window of 450 ps. Complementary time-resolved photoluminescence experiments, detecting the emission at the exciton energy under the same pump conditions, show the PL intensity in resonant and nonresonant cases to be similar. The counter-intuitive existence of luminescence at the exciton energy simultaneously with the absence of the s-2p absorption is consistent with the recent theoretical predictions of Kira et al., Phys. Rev. Lett. 81, 3263 (1998).

    P. Rauter, T. Fromherz, N. Q. Vinh, B. N. Murdin, J. P. Phillips, C. R. Pidgeon, L. Diehl, G. Dehlinger, D. Grützmacher, Ming Zhao, Wei-Xin Ni, G. Bauer (2007)Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments, In: New Journal of Physics9(128)

    We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump–pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump–pump photocurrent experiments at a free electron laser (wavelength 7.9 μm) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump–pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1–HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump–probe experiments.

    K. L. Litvinenko, L. Nikzad, C. R. Pidgeon, J. Allam, L. F. Cohen, T. Ashley, M. Emeny, W. Zawadzki, B. N. Murdin (2008)Temperature dependence of the electron Landé g factor in InSb and GaAs, In: Physical Review B77(033204)

    We report Larmor precession in bulk InSb observed in the time domain from 77 to 300 K. The optically oriented polarization precesses coherently even at 300 K. The inferred Zeeman spin splitting is strongly nonparabolic, and the electron g factor (g*) is in good agreement with k·p theory (provided we take only the dilational contribution to the change in energy gap with temperature). We also show here that correct application of the 14-band k·p model agrees with apparently anomalous trends previously reported for GaAs and confirm that the most widely quoted formula for g* in GaAs is incomplete.

    P. C. Findlay, J-P. R. Wells, I. V. Bradley, J. G. Crowder, C. R. Pidgeon, B. N. Murdin, M. J. Yang, I. Vurgaftman, J. R. Meyer (2000)Suppression of Auger recombination in long-wavelength quantum well W-structure lasers, In: Physical Review B62(10297)pp. 10297-10300
    M Merrick, S A Cripps, B N Murdin, T J Hosea, T D Veal, C F McConville, M Hopkinson (2007)Photoluminescence of InNAs alloys: S-Shaped Temperature Dependence and Conduction-Band Nonparabolicity, In: Physical Review B76(7)

    Photoluminescence (PL) has been used as a means of unambiguously observing band gap reduction in InNAs epilayers grown by molecular beam epitaxy. The observed redshift in room temperature emission as a function of nitrogen concentration is in agreement with the predictions of the band anticrossing (BAC) model, as implemented with model parameters derived from tight-binding calculations. The temperature dependence of the emission from certain samples exhibits a signature non-Varshni-like behavior indicative of electron trapping in nitrogen-related localized states below the conduction-band edge, as predicted by the linear combination of isolated nitrogen states (LCINS) model. This non-Varshni-like behavior tends to grow more pronounced with increasing nitrogen content, but for the highest nitrogen concentration studied, the more familiar Varshni-like behavior is recovered. Although unexpected, this observation is found to be consistent with the BAC and LCINS models. With consideration given to the effects of conduction-band nonparabolicity on the emission line shapes, the BAC model parameters extracted from the measured PL transition energies are found to be in excellent agreement with the predictions of the aforementioned tight-binding calculations.

    S. D. Ganichev, Petra Schneider, V. V. Bel'kov, E. L. Ivchenko, S. A. Tarasenko, W. Wegscheider, D. Weiss, D. Schuh, B. N. Murdin, P. J. Phillips, C. R. Pidgeon, D. G. Clarke, M. Merrick, P. Murzyn, E. V. Beregulin, W. Prettl (2003)Spin-galvanic effect due to optical spin orientation in n-type GaAs quantum well structures, In: Physical Review B68(081302)

    Under oblique incidence of circularly polarized infrared radiation the spin-galvanic effect (SGE) has been unambiguously observed in (001)-grown n-type GaAs quantum well structures in the absence of any external magnetic field. Resonant intersubband transitions have been obtained making use of the tunability of the free-electron laser FELIX. A microscopic theory of the SGE for intersubband transitions has been developed, which is in good agreement with experimental findings.

    Stephen A. Lynch, Douglas J. Paul, Paul Townsend, Guy Matmon, Zhang Suet, Robert W. Kelsall, Zoran Ikonic, Paul Harrison, Jing Zhang, David J. Norris, Anthony G. Cullis, Carl R. Pidgeon, Pawel Murzyn, Ben Murdin, Mike Bain, Harry S. Gamble, Ming Zhao, Wei-Xin Ni (2006)Toward Silicon-Based Lasers for Terahertz Sources, In: IEEE Journal of Selected Topics in Quantum Electronics12(6)pp. 1570-1578

    Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried silicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser

    P. Rauter, T. Fromherz, G. Bauer, N. Q. Vinh, B. N. Murdin, J. P. Phillips, C. R. Pidgeon, L. Diehl, G. Dehlinger, D. Grützmacher (2006)Direct monitoring of the excited state population in biased SiGe valence band quantum wells by femtosecond resolved photocurrent experiments, In: Applied Physics Letters211111(2006)

    The authors report a direct measurement of the optical phonon intersubband hole relaxation time in a SiGe heterostructure and a quantitative determination of hole relaxation under electrically active conditions. The results were obtained by femtosecond resolved pump-pump photocurrent experiments using a free electron laser (wavelength 7.9 µm). Additionally, the intensity dependence of the nonlinear photocurrent response was measured. Both types of experiments were simulated using a density matrix description. With one parameter set, a consistent modeling was achieved confirming the significance of the extracted heavy hole relaxation times. For an intersublevel spacing of 160 meV, a value of 550 fs was obtained.

    Tomas Peach, Kevin Homewood, Manon Lourenco, M Hughes, Kaymar Saeedi, Nikolaos Stavrias, Juerong Li, Steven Chick, Benedict Murdin, Steven Clowes (2018)The Effect of Lattice Damage and Annealing Conditions on the Hyperfine Structure of Ion Implanted Bismuth Donors in Silicon, In: Advanced Quantum Technologies1(2)1800038 Wiley
    This study reports on high energy bismuth ion implantation into silicon with a particular emphasis on the effect that annealing conditions have on the observed hyperfine structure of the Si:Bi donor state. A suppression of donor bound exciton, D0X, photoluminescence is observed in implanted samples which have been annealed at 700 °C relating to the presence of a dense layer of lattice defects that is formed during the implantation process. Hall measurments at 10 K show that this implant damage manifests itself at low temperatures as an abundance of p‐type charge carriers, the density of which is observed to have a strong dependence on annealing temperature. Using resonant D0X photoconductivity, we are able to identify the presence of a hyperfine structure in samples annealed at a minimum temperature of 800 °C; however, higher temperatures are required to eliminate effects of implantation strain.
    C. J. Dent, B. N. Murdin, I. Galbraith (2003)Phase and intensity dependence of the dynamical Franz-Keldysh effect, In: Physical Review B67(165312)

    We present theoretical results on the nonlinear optics of semiconductor quantum wells in intense THz electric fields (the dynamic Franz-Keldysh effect or DFKE). The absorption spectra show a rich variety of behavior, including THz replicas of the 2p exciton and THz sidebands of the 1s exciton. We calculate the dependence of these features on the phase and intensity of the THz field using the extended semiconductor Bloch equations, and discuss the relevance of our results to future experiments. The 1s-sideband absorption feature shows a strong dependence on the phase of the THz field, and phase averages to zero. We also discuss the relative advantages and disadvantages of reflectivity and absorption spectroscopies for probing the DFKE.

    R. Chari, I. Galbraith, J. Phillips, S. Pellegrini, C. J. Dent, A. K. Kar, G. S. Buller, C. R. Pidgeon, D. G. Clarke, B. N. Murdin, J. Allam, A. F. G. van der Meer, G. Strasser (2003)Excitonic signatures in photoluminescence and terahertz absorption

    By measuring THz absorption and time-resolved photoluminescence on the same GaAs quantum well sample we confirm the recent prediction of Kira that PL at the exciton frequency does not require a population of bound excitons.

    K. Saeedi, N. Stavrias, B. Redlich, H. Riemann, N.V. Abrosimov, P. Becker, H-J. Pohl, M.L.W. Thewalt, Benedict Murdin (2018)Short lifetime components in the relaxation of boron acceptors in silicon, In: Physical Review B97(12)125205pp. 125205-1 American Physical Society
    We present time-resolved measurements of the relaxation between the orbital states of the shallow acceptor boron in silicon. The silicon host was enriched Si-28, which exhibits life-time broadened absorption lines. We observed a wide range of T1 lifetimes from 6ps to 130ps depending on the excited state and the pump intensity. The fastest transients have not been observed previously in the time domain, and they are caused by the phonon relaxation responsible for the small-signal frequency domain line-width. We identify the slower components with an ionisation/recombination/cascade pathway.
    S A Lynch, D J Paul, P Townsend, G Matmon, Z Suet, R W Kelsall, Z Ikonic, P Harrison, J Zhang, D J Norris, A G Culllis, C R Pidgeon, P Murzyn, B Murdin, M Bain, H S Gamble, M Zhao, W X Ni (2006)Toward Silicon-Based Lasers for Terahertz Sources, In: IEEE Journal of Selected Topics in Quantum Electronics12(6)

    Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried silicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser.

    P Murzyn, C R Pidgeon, P J Phillips, M Merrick, K L Litvinenko, J Allam, B N Murdin, T Ashley, J H Jefferson, A Miller, L F Cohen (2005)Erratum: Suppression of D'yakonov-Perel Spin Relaxation in InAs and InSb by n-Type Doping at 300 K (vol 83, pg 5220, 2003), In: Applied Physics Letters87(12)
    M. Merrick, S. A. Cripps, B. N. Murdin, T.J. C. Hosea, T. D. Veal, C. F. McConville, M. Hopkinson (2007)Photoluminescence of InNAs alloys: S-shaped temperature dependence and conduction-band nonparabolicity, In: Physical Review B76(075209)

    Photoluminescence (PL) has been used as a means of unambiguously observing band gap reduction in InNAs epilayers grown by molecular beam epitaxy. The observed redshift in room temperature emission as a function of nitrogen concentration is in agreement with the predictions of the band anticrossing (BAC) model, as implemented with model parameters derived from tight-binding calculations. The temperature dependence of the emission from certain samples exhibits a signature non-Varshni-like behavior indicative of electron trapping in nitrogen-related localized states below the conduction-band edge, as predicted by the linear combination of isolated nitrogen states (LCINS) model. This non-Varshni-like behavior tends to grow more pronounced with increasing nitrogen content, but for the highest nitrogen concentration studied, the more familiar Varshni-like behavior is recovered. Although unexpected, this observation is found to be consistent with the BAC and LCINS models. With consideration given to the effects of conduction-band nonparabolicity on the emission line shapes, the BAC model parameters extracted from the measured PL transition energies are found to be in excellent agreement with the predictions of the aforementioned tight-binding calculations.

    B Wittmann, SN Danilov, VV Bel'kov, SA Tarasenko, EG Novik, H Buhmann, C Brüne, LW Molenkamp, ZD Kvon, NN Mikhailov, SA Dvoretsky, NQ Vinh, AFGVD Meer, B Murdin, SD Ganichev (2010)Circular photogalvanic effect in HgTe/CdHgTe quantum well structures, In: arXiv
    We describe the observation of the circular and linear photogalvanic effects in HgTe/CdHgTe quantum wells. The interband absorption of mid-infrared radiation as well as the intrasubband absorption of terahertz (THz) radiation in the QWs structures is shown to cause a dc electric current due to these effects. The photocurrent magnitude and direction varies with the radiation polarization state and crystallographic orientation of the substrate in a simple way that can be understood from a phenomenological theory. The observed dependences of the photocurrent on the radiation wavelength and temperature are discussed.
    W Weber, LE Golub, SN Danilov, J Karch, C Reitmaier, B Wittmann, VV Bel'kov, EL Ivchenko, ZD Kvon, NQ Vinh, AFG van der Meer, B Murdin, SD Ganichev (2008)Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures, In: PHYSICAL REVIEW B77(24)ARTN 2pp. ?-? AMER PHYSICAL SOC
    SN Danilov, B Wittmann, P Olbrich, W Eder, W Prettl, LE Golub, EV Beregulin, ZD Kvon, NN Mikhailov, SA Dvoretsky, VA Shalygin, NQ Vinh, AFG van der Meer, B Murdin, SD Ganichev (2009)Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures, In: JOURNAL OF APPLIED PHYSICS105(1)ARTN 0pp. ?-? AMER INST PHYSICS
    Kamyar Saeedi, Nikolas Stavrias, Britta Redlich, A.F.G. van der Meer, Rostislav Mikhaylovskiy, Alexey V Kimel, C R Pidgeon, B N Murdin (2019)Spin preservation during THz orbital pumping of shallow donors in silicon, In: Journal of Physics: Condensed Matter IOP Publishing
    We investigate the spin relaxation under conditions of optical excitation between the Rydberg orbital states of phosphorus donor impurities in silicon. Here we show that the spin relaxation is less than a few percent, even after multiple excitation/relaxation cycles. The observed high level of spin preservation may be useful for readout cycling or in quantum information schemes where coupling of neighbor qubits is via orbital excitation.
    P Murzyn, C R Pidgeon, P J Phillips, M Merrick, K L Litvinenko, J Allam, B N Murdin, T Ashley, J H Jefferson, A Miller, L F Cohen (2003)Suppression of D'yakonov-Perel Spin Relaxation in InAs and InSb by n-Type Doping at 300 K, In: Applied Physics Letters83(25)

    We have made direct pump-probe measurements of spin lifetimes in intrinsic and degenerate n-InAs at 300 K. In particular, we measure remarkably long spin lifetimes (tau(s)similar to1.6 ns) for near-degenerate epilayers of n-InAs. For intrinsic material, we determine tau(s)similar to20 ps, in agreement with other workers. There are two main models that have been invoked for describing spin relaxation in narrow-gap semiconductors: the D'yakonov-Perel (DP) model and the Elliott-Yafet (EY) model. For intrinsic material, the DP model is believed to dominate in III-V materials above 77 K, in agreement with our results. We show that in the presence of strong n-type doping, the DP relaxation is suppressed both by the degeneracy condition and by electron-electron scattering, and that the EY model then dominates for the n-type material. We show that this same process is also responsible for a hitherto unexplained lengthening of tau(s) with n-type doping in our earlier measurements of n-InSb.

    I Galbraith, R Chari, S Pellegrini, P J Phillips, C J Dent, A F van der Meer, D G Clarke, A K Kar, G S Buller, C R Pidgeon, B N Murdin, J Allam, G Strasser (2005)Excitonic Signatures in the Photoluminescence and Terahertz Absorption of a GaAs/AlxGa1-xAs Multiple Quantum Well, In: Physical Review B71(7)

    Measurements of the THz absorption and the time-resolved photoluminescence have been performed on the same GaAs quantum well sample. The strength of the absorption at the internal 1s-2p exciton transition frequency is used as a measure of the density of excitons in the sample. When the interband pump laser is resonant with the Is exciton frequency, induced absorption at the 1s-2p frequency is clearly seen. If the same density of carriers is created pumping in the continuum, no significant 1s-2p absorption is seen in a time window of 450 ps. Complementary time-resolved photoluminescence experiments, detecting the emission at the exciton energy under the same pump conditions, show the PL intensity in resonant and nonresonant cases to be similar. The counter-intuitive existence of luminescence at the exciton energy simultaneously with the absence of the 1s-2p absorption is consistent with the recent theoretical predictions of Kira et al., Phys. Rev. Lett. 81, 3263 (1998).

    P. C. Findlay, C. R. Pidgeon, R. Kotitschke, A. Hollingworth, B. N. Murdin, C. J. G. M. Langerak, A. F. G. van der Meer, C. M. Ciesla, J. Oswald, A. Homer, G. Springholz, G. Bauer (1998)Auger recombination dynamics of lead salts under picosecond free-electron-laser excitation, In: Physical Review B58(12908)pp. 12908-12915

    Pump-probe transmission experiments have been performed on PbSe above the fundamental absorption edge near 4 μm in the temperature range 30 to 300 K, using the Dutch ps free-electron laser. For temperatures below 200 K and carrier densities above the threshold for stimulated emission, stimulated recombination represents the most efficient recombination mechanism with relatively fast kinetics in the 50–100-ps regime, in good agreement with earlier reports of photoluminescent emission. Above this temperature Auger recombination dominates, and the Auger coefficient C is determined from the pump-probe decay curves. In the low-temperature regime the Auger coefficient is determined from the decay curves at times beyond 100 ps. The Auger coefficient is approximately constant (with a value of about 8×10-28 cm6 s-1) between 300 and 70 K, and then drops a value of about 1×10-28 cm6 s-1 at 30 K, in good agreement with the theory for nonparabolic near-mirror bands and nondegenerate statistics. It is found that C for PbSe is between one and two orders of magnitude lower than for Hg1-xCdxTe of comparable band gap.

    T D Veal, L F Piper, P H Jefferson, I Mahboob, C F McConville, M Merrick, T J Hosea, B N Murdin, M Hopkinson (2005)Photoluminescence Spectroscopy of Bandgap Reduction in Dilute InNAs Alloys, In: Applied Physics Letters87(18)

    Photoluminescence (PL) has been observed from dilute InNxAs1-x epilayers grown by molecular-beam epitaxy. The PL spectra unambiguously show band gap reduction with increasing N content. The variation of the PL spectra with temperature is indicative of carrier detrapping from localized to extended states as the temperature is increased. The redshift of the free exciton PL peak with increasing N content and temperature is reproduced by the band anticrossing model, implemented via a (5x5) k center dot p Hamiltonian.

    K L Litvinenko, B N Murdin, J Allam, C R Pidgeon, M Bird, K Morris, W Branford, S K Clowes, L F Cohen, T Ashley, L Buckle (2006)Spin Relaxation in N-InSb/AlInSb Quantum Wells, In: New Journal of Physics8(4)

    We have used time resolved spectroscopy to measure the relaxation of spin polarization in InSb/AlInSb quantum wells (QWs) as a function of temperature and mobility. The results are consistent with the D'yakonov - Perel (DP) mechanism for high mobility samples over the temperature range from 50 to 300 K. For low mobility samples at high temperature the Elliott - Yafet and DP mechanisms become comparable. We show that the mobility can in certain circumstances determine which mechanism is dominant, and that above 1 m(2) V-1 s(-1) in 20 nm wide InSb QWs it is the DP mechanism. We also give a criterion for the maximum spin lifetime in terms of mobility and temperature, and show that for our 20 nm wide QWs this corresponds to 0.5 ps at 300 K and mobility 1 m(2) V-1 s(-1).

    P. Murzyn, C. R. Pidgeon, P. J. Phillips, M. Merrick, K. L. Litvinenko, J. Allam, B. N. Murdin, T. Ashley, J. H. Jefferson, A. Miller, L. F. Cohen (2003)Suppression of D'yakonov–Perel spin relaxation in InAs and InSb by n-type doping at 300 K, In: Applied Physics Letters5220(2003)
    SA Lynch, DJ Paul, P Townsend, G Matmon, RW Kelsall, Z Ikonic, P Harrison, J Zhang, DJ Norris, AG Cullis, CR Pidgeon, P Murzyn, B Murdin, M Bain, HS Gamble (2005)Silicon quantum cascade lasers for THz sources, In: 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS)pp. 727-728
    B N Murdin, K Litvinenko, D G Clarke, C R Pidgeon, P Murzyn, P J Phillips, D Carder, G Berden, B Redlich, A F van der Meer, S Clowes, J J Harris, L F Cohen, T Ashley, L Buckle (2006)Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, In: Physical Review Letters96(9)

    We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the case of the material chosen, n-InSb, the increase was from 14 to 38 ps.

    Y Andreev, AE Kokh, KA Kokh, GV Lanskii, Konstantin Litvinenko, AA Mamrashev, JF Molloy, Benedict Murdin, M Naftaly, NA Nikolaev, VA Svetlichnyi (2017)Observation of a different birefringence order at optical and THz frequencies in LBO crystal, In: Optical Materials66pp. 94-97 Elsevier
    THz optical properties of lithium borate (LBO) crystals were measured using time-domain spectroscopy (TDS). The LBO crystal samples were of high optical quality and were cut and polished along the h100i, h010i and h001i axes. Two independent measurements were performed in order to con rm the reproducibility and consistency of results. The contradictions in the previously published data on the THz optical properties of LBO were clari ed. It was shown that the birefringence order at THz frequencies is nz < nx < ny, whereas at optical frequencies it is known to be nx < ny < nz. It was seen that nz, which has the highest value in the visible, has the lowest value at THz. This is explained in terms of ionic polarizability and is consistent with the fact that the THz absorption coe cient for a wave polarized along the Z-axis is more than an order of magnitude lower than for the X and Y axes. Absorption as low as 0.2 cm 1 was found at frequencies up to 0.5 THz for a wave polarized parallel to the Z-axis. A set of new dispersion equations was designed for the entire transparency range.
    Marco Califano, N. Q. Vinh, P. J. Phillips, Z. Ikonić, R. W. Kelsall, P. Harrison, C. R. Pidgeon, B. N. Murdin, D. J. Paul, P. Townsend, J. Zhang, I. M. Ross, A.G. Cullis (2007)Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: Role of interface roughness, In: Physical Review B75(045338)

    We report the direct determination of nonradiative lifetimes in Si/SiGe asymmetric quantum well structures designed to access spatially indirect (diagonal) interwell transitions between heavy-hole ground states, at photon energies below the optical phonon energy. We show both experimentally and theoretically, using a six-band k·p model and a time-domain rate equation scheme, that, for the interface quality currently achievable experimentally (with an average step height 1 greater than or equal to Å), interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recently published experimental and theoretical data obtained for mid-infrared GaAs/AlxGa1−xAs multiple quantum well systems leads us to the conclusion that the dominant role of interface roughness scattering at low temperature is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV materials.

    C. R. Pidgeon, P. Murzyn, J.-P. R. Wells, N. T. Gordon, T. Ashley, J. H. Jefferson, T. M. Burke, C. D. Maxey, B. N. Murdin (2002)Electron spin coherence in long wavelength Hg 1-xCd xTe, In: Twenty Seventh International Conference on Infrared and Millimeter Wavespp. 25-26
    M Califano, N Q Vinh, P J Phillips, Z Ikonic, R W Kelsall, P Harrison, C R Pidgeon, B N Murdin, D J Paul, P Townsend, J Zhang, I M Ross, A G Cullis (2007)Interwell Relaxation Times in p-Si/SiGe Asymmetric Quantum Well Structures: Role of Interface Roughness, In: Physical Review B75(4)

    We report the direct determination of nonradiative lifetimes in Si/SiGe asymmetric quantum well structures designed to access spatially indirect (diagonal) interwell transitions between heavy-hole ground states, at photon energies below the optical phonon energy. We show both experimentally and theoretically, using a six-band k center dot p model and a time-domain rate equation scheme, that, for the interface quality currently achievable experimentally (with an average step height >= 1 A), interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recently published experimental and theoretical data obtained for mid-infrared GaAs/AlxGa1-xAs multiple quantum well systems leads us to the conclusion that the dominant role of interface roughness scattering at low temperature is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV materials.

    W Weber, L E Golub, S N Danilov, J Karch, C Reitmaier, B Wittmann, W Bel'kov, E L Ivchenko, Z D Kvon, N Q Vinh, A F van der Meer, B Murdin, S D Ganichev (2008)Quantum Ratchet Effects Induced by Terahertz Radiation in GaN-Based Two-Dimensional Structures, In: Physical Review B77(24)

    Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.

    B. N. Murdin, K. Litvinenko, J. Allam, C. R. Pidgeon, M. Bird, K. Morrison, T. Zhang, S. K. Clowes, W. R. Branford, J. Harris, L. F. Cohen (2005)Temperature and doping dependence of spin relaxation in n-InAs, In: Physical Review B72(085346)

    We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in the narrow gap semiconductor material n-InAs as a function of temperature, doping, and pump wavelength. The results are consistent with the D'Yakonov-Perel mechanism for temperatures between 77 and 300 K. However, the data suggest that electron-electron scattering should be taken into account in determining the dependence of the spin lifetime on the carrier concentration in the range 5.2×1016–8.8×1017 cm–3. For a sample with doping of 1.22×1017 cm–3 the spin lifetime was 24 ps at room temperature. By applying a magnetic field in the sample plane we also observed coherent precession of the spins in the time domain, with a g>/i> factor g*=–13, also at room temperature.

    P. Murzyn, C. R. Pidgeon, P. J. Phillips, J-P. Wells, N. T. Gordon, T. Ashley, J. H. Jefferson, T. M. Burke, J. Giess, M. Merrick, B. N. Murdin, C. D. Maxey (2003)Electron spin lifetimes in long-wavelength Hg1-xCdxTe and InSb at elevated temperature, In: Physical Review B67(235202)
    C. R. Pidgeon, P. Murzyn, J.-P. R. Wells, N. T. Gordon, T. Ashley, J. H. Jefferson, T. M. Burke, C. D. Maxey, B. N. Murdin (2002)Electron spin coherence in long wavelength Hg 1-xCd xTe, In: Twenty Seventh International Conference on Infrared and Millimeter Wavespp. 25-26
    K L Litvinenko, L Nikzad, J Allam, B N Murdin, C R Pidgeon, J J Harris, T Zhang, L F Cohen (2007)Spin Lifetime in High Quality InSb Epitaxial Layers Grown on GaAs, In: Journal of Applied Physics101(8)

    The spin relaxation in undoped InSb films grown on GaAs has been investigated in the temperature range from 77 to 290 K. Two distinct lifetime values have been extracted, 1 and 2.5 ps, dependent on film thickness. Comparison of this data with a multilayer transport analysis of the films suggests that the longer time (similar to 2.5 ps at 290 K) is associated with the central intrinsic region of the film, while the shorter time (similar to 1 ps) is related to the highly dislocated accumulation region at the film-substrate interface. Whereas previous work on InAs films grown on GaAs showed that the native surface defect resulted in an additional charge accumulation layer with high conductivity but very short spin lifetime, in InSb layers the surface states introduce a depletion region. We infer that InSb could be a more attractive candidate for spintronic applications than InAs.

    B. N. Murdin, A. R. Hollingworth, J. A. Barker, D. G. Clarke, P. C. Findlay, C. R. Pidgeon, J.-P. R. Wells, I. V. Bradley, S. Malik, R. Murray (2000)Double-resonance spectroscopy of InAsÕGaAs self-assembled quantum dots, In: Physical Review B62(12) American Physical Society

    We present far-/near-infrared double resonance measurements of self-assembled InAs/GaAs quantum dots. The far-infrared resonance is unambiguously associated with a bound-bound intraband transition in the neutral dots. The results show that the interband photoluminescence (PL) lines originate from conduction levels with successively increasing in-plane quantum numbers. We determine the confinement energies for both electrons and holes in the same dots. Furthermore, we show that the inhomogeneous broadening of the PL cannot be attributed solely to size and composition fluctuation.

    We model theoretically the dependence of excitonic absorption spectra of semiconductor quantum wells in intense THz electric fields on the phase and intensity of those fields, and discuss the implications of our results for experiment.

    K. L. Litvinenko, B. N. Murdin, J. Allam, C. R. Pidgeon, T. Zhang, J. J. Harris, L. F. Cohen, D. A. Eustace, D. W. McComb (2006)Spin lifetime in InAs epitaxial layers grown on GaAs, In: Physical Review B74(075331)

    We report investigation of the spin relaxation in InAs films grown on GaAs at a temperature range from 77 K to 290 K. InAs is known to have a surface accumulation layer and the depth profile of the concentration and mobility is strongly nonuniform. We have correlated the spin relaxation with a multilayer analysis of the transport properties and find that the surface and the interface with the GaAs substrate both have subpicosecond lifetimes (due to the high carrier concentration), whereas the central semiconducting layer has a lifetime of an order of 10 ps. Even for the thickest film studied (1 micro-m, the semiconducting layer only carried 30% of the total current (with 10% through the interface layer and 60% through the surface accumulation layer). Designs for spintronic devices that utilize InAs, which is attractive due to its narrow gap and strong Rashba effect, will need to include strategies for minimizing the effects of the surface.

    P Rauter, T Fromherz, G Bauer, N Q Vinh, B N Murdin, J P Phillips, C R Pidgeon, L Diehl, G Dehlinger, D Grutzmacher (2006)Direct Monitoring of the Excited State Population in Biased SiGe Valence Band Quantum Wells by Femtosecond Resolved Photocurrent Experiments, In: Applied Physics Letters89(21)

    The authors report a direct measurement of the optical phonon intersubband hole relaxation time in a SiGe heterostructure and a quantitative determination of hole relaxation under electrically active conditions. The results were obtained by femtosecond resolved pump-pump photocurrent experiments using a free electron laser (wavelength 7.9 mu m). Additionally, the intensity dependence of the nonlinear photocurrent response was measured. Both types of experiments were simulated using a density matrix description. With one parameter set, a consistent modeling was achieved confirming the significance of the extracted heavy hole relaxation times. For an intersublevel spacing of 160 meV, a value of 550 fs was obtained. (c) 2006 American Institute of Physics.

    K. L. Litvinenko, B. N. Murdin, J. Allam, C. R. Pidgeon, M. Bird, K. Morris, W. Branford, S. K. Clowes, L. F. Cohen, T. Ashley, L. Buckle (2006)Spin relaxation in n-InSb/AlInSb quantum wells, In: New Journal of Physics8(4)

    We have used time resolved spectroscopy to measure the relaxation of spin polarization in InSb/AlInSb quantum wells (QWs) as a function of temperature and mobility. The results are consistent with the D'yakonov–Perel (DP) mechanism for high mobility samples over the temperature range from 50 to 300 K. For low mobility samples at high temperature the Elliott–Yafet and DP mechanisms become comparable. We show that the mobility can in certain circumstances determine which mechanism is dominant, and that above 1 m2 V-1 s-1 in 20 nm wide InSb QWs it is the DP mechanism. We also give a criterion for the maximum spin lifetime in terms of mobility and temperature, and show that for our 20 nm wide QWs this corresponds to 0.5 ps at 300 K and mobility 1 m2 V-1 s-1.

    P. Rauter, T. Fromherz, G. Bauer, N. Q. Vinh, P. J. Phillips, C. R. Pidgeon, B. N. Murdin, L. Diehl, G. Dehlinger, D. Grutzmacher (2006)Direct Measurement of HH2-HH1 Intersubband Lifetimes in SiGe Quantum Cascade Structurespp. 1-2
    T. D. Veal, L. F. J. Piper, S. Jollands, B. R. Bennett, P. H. Jefferson, P. A. Thomas, C. F. McConville, B. N. Murdin, L. Buckle, G. W. Smith, T. Ashley (2005)Band gap reduction in GaNSb alloys due to the anion mismatch, In: Applied Physics Letters132101(2005)

    The structural and optoelectronic properties in GaNxSb1−x alloys (0≤x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1−x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content.

    R. A. Child, R. J. Nicholas, N. J. Mason, P. A. Shields, J-P. R. Wells, I. V. Bradley, J. Phillips, B. N. Murdin (2003)Far-infrared modulated photoluminescence spectroscopy of InSb/GaSb quantum dot structures, In: Physical Review B68(165307)

    The first far-infrared modulated photoluminescence (FIRM-PL) measurements in InSb/GaSb quantum dots have been performed. Far-infrared absorption is found to both enhance and suppress the quantum dot PL depending on the FIR intensity. This behavior is attributed to the nonthermal distribution of carriers amongst the quantum dots. The spectral dependence of the FIRM-PL signal measures the energy spectrum of the quantum dots, showing a peak at 14.5 meV corresponding to transitions between the first two energy levels of the dot distribution.

    PH Jefferson, TD Veal, LFJ Piper, BR Bennett, CF McConville, BN Murdin, L Buckle, GW Smith, T Ashley (2006)Band anticrossing in GaNxSb1-x, In: APPLIED PHYSICS LETTERS89(11)ARTN 1pp. ?-? AMER INST PHYSICS
    B. N. Murdin, K. Litvinenko, D. G. Clarke, C. R. Pidgeon, P. Murzyn, P. J. Phillips, D. Carder, G. Berden, B. Redlich, A. F. G. van der Meer, S. Clowes, J. J. Harris, L. F. Cohen, T. Ashley, L. Buckle (2006)Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, In: Physical Review Letters96(096603)

    We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the case of the material chosen, n-InSb, the increase was from 14 to 38 ps.

    K L Litvinenko, B N Murdin, J Allam, C R Pidgeon, T Zhang, J J Harris, L F Cohen, D A Eustace, D W McComb (2006)Spin Lifetime in InAs Epitaxial Layers Grown on GaAs, In: Physical Review B74(7)

    We report investigation of the spin relaxation in InAs films grown on GaAs at a temperature range from 77 K to 290 K. InAs is known to have a surface accumulation layer and the depth profile of the concentration and mobility is strongly nonuniform. We have correlated the spin relaxation with a multilayer analysis of the transport properties and find that the surface and the interface with the GaAs substrate both have subpicosecond lifetimes (due to the high carrier concentration), whereas the central semiconducting layer has a lifetime of an order of 10 ps. Even for the thickest film studied (1 mu m), the semiconducting layer only carried 30% of the total current (with 10% through the interface layer and 60% through the surface accumulation layer). Designs for spintronic devices that utilize InAs, which is attractive due to its narrow gap and strong Rashba effect, will need to include strategies for minimizing the effects of the surface.

    B. N. Murdin, A. R. Hollingworth, M. Kamal-Saadi, R. T. Kotitschke, C. M. Ciesla, C. R. Pidgeon, P. C. Findlay, H. P. M. Pellemans, C. J. G. M. Langerak, A. C. Rowe, R. A. Stradling, E. Gornik (1999)Suppression of LO phonon scattering in Landau quantized quantum dots, In: Physical Review B59(12)

    Picosecond time-resolved far-infrared measurements are presented of the scattering between conduction-band states in a doped quasi quantum dot. These states are created by the application of a magnetic field along the growth direction of an InAs/AlSb quantum well. A clear suppression of the cooling rate is seen, from 1012 s-1 when the level spacing is equal to the phonon energy, to 1010 s-1 away from this resonance, and thus the results provide unambiguous evidence for the phonon bottleneck. Furthermore, the lifetimes had only weak dependence on temperature between 4 and 80 K.

    P Rauter, T Fromherz, N Q Vinh, B N Murdin, J P Phillips, C R Pidgeon, L Diehl, G Dehlinger, D Grutzmacher, M Zhao, W X Ni, G Bauer (2007)Direct Determination of Ultrafast Intersubband Hole Relaxation Times in Voltage Biased SiGe Quantum Wells by a Density Matrix Interpretation of Femtosecond Resolved Photocurrent Experiments, In: New Journal of Physics9(5)

    We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 mu m) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump-probe experiments.

    T. D. Veal, L. F. J. Piper, P. H. Jefferson, I. Mahboob, C. F. McConville, M. Merrick, T. J. C. Hosea, B. N. Murdin, M. Hopkinson (2005)Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys, In: Applied Physics Letters182114(2005)

    Photoluminescence (PL) has been observed from dilute InNxAs1–x epilayers grown by molecular-beam epitaxy. The PL spectra unambiguously show band gap reduction with increasing N content. The variation of the PL spectra with temperature is indicative of carrier detrapping from localized to extended states as the temperature is increased. The redshift of the free exciton PL peak with increasing N content and temperature is reproduced by the band anticrossing model, implemented via a (5×5) k·p Hamiltonian.

    RP Green, A Tredicucci, NQ Vinh, B Murdin, C Pidgeon, HE Beere, DA Ritchie (2009)Gain recovery dynamics of a terahertz quantum cascade laser, In: PHYSICAL REVIEW B80(7)ARTN 0pp. ?-? AMER PHYSICAL SOC
    T D Veal, L F Piper, S Jollands, B R Bennett, P H Jefferson, P A Thomas, C F McConville, B N Murdin, L Buckle, G W Smith, T Ashley (2005)Band Gap Reduction in GaNSb Alloys Due to the Anion Mismatch, In: Applied Physics Letters87(13)

    The structural and optoelectronic properties in GaNxSb1-x alloys (0 <= x < 0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1-x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content. (C) 2005 American Institute of Physics.

    A. M. Gilbertson, M. Fearn, J. H. Jefferson, B. N. Murdin, P. D. Buckle, L. F. Cohen (2008)Zero-field spin splitting and spin lifetime in n-InSb/In1−xAlxSb asymmetric quantum well heterostructures, In: Physical Review B77(165335)
    This report discusses new understanding of the fundamental links between the micro- and nano-structure of silver nanowire-based transparent conductive films and their resulting macroscopic electrical and optical properties. A new relationship between the optical transmittance and electrical sheet resistance is derived based on percolation theory. Application of this model to experimental data allows parameters of film micro-structure to be determined using macroscopic measurement techniques. Conversely, it is also possible to tailor the optoelectronic properties of a film by manipulation of the length distribution of the constituent nanowire material. Further, we examine the effect of geometrical confinement on silver nanowire networks. It is observed that as feature sizes decrease below some threshold value, there is a rapid increase of sheet resistance. This is understood in terms of finite-size scaling theory, and is linked to film parameters that can be measured from the transmittance-sheet resistance curve (T-R curve) of a given material. The effect is quantified using experimental and simulation data, and the implications for device structure and design are discussed. Expressions describing both the T-R and finite-size scaling responses of a material are derived in terms of length distribution statistics, which allows a deeper understanding of how materials may be tailored to meet application-specific requirements. Finally, a preliminary investigation of the formation of graphene-silver nanowire hybrid electrodes by mechanical transfer deposition of graphene is performed. The T-R model developed is applied to understand the change in film performance (in terms of the T-R response). It is hoped that further development of the work presented will lead to a coherent framework for quantifying and predicting a range of film properties for nanowire materials. This will facilitate material design and speed up optimisation of materials for specific applications, both in academic and industrial settings.
    Quantum computation holds the promise of efficient solutions to currently formidable problems. A prospective technology is that of computing using quantum states, which may dramatically speed up or otherwise reduce the complexity for the solution of some hard problems. Of the many different schemes proposed, shallow substitutional donors in Silicon hold great attractiveness for the detailed study of the medium, high industrial capacity, and ubiquity of raw materials. We develop control over the quantum orbital and spin states of bound electrons using the THz ultrafast laser FELIX. Manipulation of orbital states is studied using interferometric methods to produce Ramsey fringes, read out using optical and electrical methods. Contactless electrical measurement of free charge carriers is implemented, and the details of its advantages and limitations are explored. Both types of readout are used to demonstrate a coherent 3-level orbital manipulation, otherwise known as a quantum beat. The work constitutes a nontrivial control over the spatial distribution of the wavefunction of the atom which may enable error correcting surface code implementations. Spin dynamics are then explored in the presence of FELIX using donor-bound exciton techniques, which allow a sensitive and fast control over the electron spin states. The implementation is used to probe whether orbital excitation has a strong effect upon the spin states of the donor electrons, and it is shown that any modification of the spin is negligible. Experimental measurements of optically gated spin-exchange coupling are enabled by this methodology, and a roadmap to future implementation is discussed in the context of the present work. Overall, the work advances the state of spin and orbital control of neutral donor states for the purposes of optically gated quantum computing. Combined spin and orbital manipulations are now possible in the system, which will allow a more advanced implementation of quantum computation using orbital states than was previously possible.