# 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

Department of Physics, Photonics and Quantum Sciences Group.

### 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

### Publications

Litvinenko KL, Murdin BN, Allam J, Pidgeon CR, Zhang T, Harris JJ, Cohen LF, Eustace DA, McComb DW (2006) Spin lifetime in InAs epitaxial layers grown on GaAs, PHYSICAL REVIEW B 74 (7) ARTN 075331 AMERICAN PHYSICAL SOC
Califano M, Vinh NQ, Phillips PJ, Ikonic Z, Kelsall RW, Harrison P, Pidgeon CR, Murdin BN, Paul DJ, Townsend P, Zhang J, Ross IM, Cullis AG (2007) Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: Role of interface roughness, PHYSICAL REVIEW B 75 (4) ARTN 045338 AMERICAN PHYSICAL SOC
Litvinenko KL, Nikzad L, Allam J, Murdin BN, Pidgeon CR, Harris JJ, Cohen LF (2007) Spin dynamics in narrow-gap semiconductor epitaxial layers, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 20 (6) pp. 461-465 SPRINGER
Danilov SN, Wittmann B, Olbrich P, Eder W, Prettl W, Golub LE, Beregulin EV, Kvon ZD, Mikhailov NN, Dvoretsky SA, Shalygin VA, Vinh NQ, van der Meer AFG, Murdin B, Ganichev SD (2009) Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures, JOURNAL OF APPLIED PHYSICS 105 (1) ARTN 013106 AMER INST PHYSICS
Litvinenko KL, Murdin BN, Clowes SK, Nikzad L, Allam J, Pidgeon CR, Branford W, Cohen LF, Ashley T, Buckle L (2008) Density and well-width dependence of the spin relaxation in n-InSb/AlInSb quantum wells, NARROW GAP SEMICONDUCTORS 2007 119 pp. 19-21 SPRINGER
Zhao M, Karim A, Ni W-X, Pidgeon CR, Phillips PJ, Carder D, Murdin BN, Fromherz T, Paul DJ (2006) Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering, JOURNAL OF LUMINESCENCE 121 (2) pp. 403-408 ELSEVIER SCIENCE BV
Litvinenko KL, Pang M, Li J, Bowyer E, Engelkamp H, Shuman VB, Portsel LM, Lodygin AN, Astrov YA, Pavlov SG, Huebers H-W, Pidgeon CR, Murdin BN (2014) High-field impurity magneto-optics of Si:Se, PHYSICAL REVIEW B 90 (11) ARTN 115204 AMER PHYSICAL SOC
Roither J, Pichler S, Kovalenko MV, Heiss W, Feychuk P, Panchuk O, Allam J, Murdin BN (2006) Two- and one-dimensional light propagations and gain in layer-by-layer-deposited colloidal nanocrystal waveguides, APPLIED PHYSICS LETTERS 89 (11) ARTN 111120 AMER INST PHYSICS
Rauter P, Fromherz T, Bauer G, Vinh NQ, Murdin BN, Phillips JP, Pidgeon CR, Diehl L, Dehlinger G, Gruetzmacher D (2006) Direct monitoring of the excited state population in biased SiGe valence band quantum wells by femtosecond resolved photocurrent experiments, APPLIED PHYSICS LETTERS 89 (21) ARTN 211111 AMER INST PHYSICS
Lynch SA, Thornton Greenland P, Van Der Meer AFG, Murdin BN, Pidgeon CR, Redlich B, Vinh NQ, Aeppli G (2010) Quantum control of phosphorus donor rydberg states in silicon, IEEE International Conference on Group IV Photonics GFP pp. 380-382
We demonstrate the first observation of a THz photon echo. We exploit the photon echo as an experimental tool to investigate the quantum coherence properties of excited donor Rydberg states of phosphorus in silicon. ©2010 IEEE.
Wittmann B, Danilov SN, Bel'kov VV, Tarasenko SA, Novik EG, Buhmann H, Bruene C, Molenkamp LW, Kvon ZD, Mikhailov NN, Dvoretsky SA, Vinh NQ, van der Meer AFG, Murdin B, Ganichev SD (2010) Circular photogalvanic effect in HgTe/CdHgTe quantum well structures, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 25 (9) ARTN 095005 IOP PUBLISHING LTD
Murdin BN, Li J, Pang ML, Bowyer ET, Litvinenko KL, Clowes SK, Engelkamp H, Pidgeon CR, Galbraith I, Abrosimov NV, Riemann H, Pavlov SG, Hübers HW, Murdin PG (2013) Si:P as a laboratory analogue for hydrogen on high magnetic field white dwarf stars., Nat Commun 4 Nature Publishing Group
Laboratory spectroscopy of atomic hydrogen in a magnetic flux density of 10(5) T (1 gigagauss), the maximum observed on high-field magnetic white dwarfs, is impossible because practically available fields are about a thousand times less. In this regime, the cyclotron and binding energies become equal. Here we demonstrate Lyman series spectra for phosphorus impurities in silicon up to the equivalent field, which is scaled to 32.8 T by the effective mass and dielectric constant. The spectra reproduce the high-field theory for free hydrogen, with quadratic Zeeman splitting and strong mixing of spherical harmonics. They show the way for experiments on He and H(2) analogues, and for investigation of He(2), a bound molecule predicted under extreme field conditions.
Ashley T, Buckle L, Smith GW, Murdin BN, Jefferson PH, Piper LFJ, Veal TD, McConville CF (2006) Dilute antimonide nitrides for very long wavelength infrared applications - art. no. 62060L, Infrared Technology and Applications XXXII, Pts 1and 2 6206 pp. L2060-L2060 SPIE-INT SOC OPTICAL ENGINEERING
Lynch SA, Paul DJ, Townsend P, Matmon G, Kelsall RW, Ikonic Z, Harrison P, Zhang J, Norris DJ, Cullis AG, Pidgeon CR, Murzyn P, Murdin B, Bain M, Gamble HS (2005) Silicon quantum cascade lasers for THz sources, 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS) pp. 727-728 IEEE
Litvinenko KL, Leontiadou MA, Li J, Clowes SK, Emeny MT, Ashley T, Pidgeon CR, Cohen LF, Murdin BN (2010) Strong dependence of spin dynamics on the orientation of an external magnetic field for InSb and InAs, APPLIED PHYSICS LETTERS 96 (11) ARTN 111107 AMER INST PHYSICS
Greenland PT, Lynch SA, van der Meer AFG, Murdin BN, Pidgeon CR, Redlich B, Vinh NQ, Aeppli G (2010) Coherent control of Rydberg states in silicon, NATURE 465 (7301) pp. 1057-U116 NATURE PUBLISHING GROUP
Lynch SA, Paul DJ, Townsend P, Matmon G, Suet Z, Kelsall RW, Ikonic Z, Harrison P, Zhang J, Norris DJ, Cullis AG, Pidgeon CR, Murzyn P, Murdin B, Bain M, Gamble HS, Zhao M, Ni W-X (2006) Toward silicon-based lasers for terahertz sources, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 12 (6) pp. 1570-1578 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
O'Brien K, Adams AR, Sweeney SJ, Jin SR, Ahmad CN, Murdin BN, Canedy CL, Vurgaftman I, Meyer JR (2007) High pressure studies of mid-infrared type-II "W" diode lasers at cryogenic temperatures, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 224-228 WILEY-V C H VERLAG GMBH
Gilbertson AM, Fearn M, Jefferson JH, Murdin BN, Buckle PD, Cohen LF (2008) Zero-field spin splitting and spin lifetime in n-InSb/In(1-x)A1(x)Sb asymmetric quantum well heterostructures (vol 77, art no 165335, 2008), PHYSICAL REVIEW B 78 (7) ARTN 079901 AMER PHYSICAL SOC
Leontiadou MA, Litvinenko KL, Clowes SK, Springholz G, Schwarzl T, Eibelhuber M, Heiss W, Pidgeon CR, Murdin BN (2011) Substantial temperature dependence of transverse electron g*-factor in lead chalcogenide multi-quantum wells, AIP Conference Proceedings 1416 pp. 178-180
We report significant temperature dependence of the transverse electron g*-factor in symmetric lead chalcogenide multi-quantum wells (MQWs). The g*-factor values were extracted from the electron Larmor precessions recorded by means of a circularly polarized pump probe technique under the influence of transverse external magnetic field (Voigt geometry) in the temperature range between 10 and 150K. The reported g*-factor values are in good agreement with theoretical predictions and available low temperature experimental data. Although temperature tuning of lead salt laser emission wavelengths has been the method of choice in these systems for many years, we demonstrate that temperature can also be used to modulate g*, and hence the spin lifetime in lead salt QW spintronic devices. © 2011 American Institute of Physics.
O'Brien K, Sweeney SJ, Adams AR, Jin SR, Ahmad CN, Murdin BN, Salhi A, Rouillard Y, Joullie A (2007) Carrier recombination mechanisms in mid-infrared GaInAsSb quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 203-207 WILEY-V C H VERLAG GMBH
Hydrostatic pressure and spontaneous emission techniques have been used to examine the important recombination mechanisms in type-I GaInAsSb/GaSb quantum well lasers. High pressure results indicate that Auger recombination dominates the threshold current of 2.11 mu m and 2.37 mu m devices and is the origin of their temperature sensitivity around room temperature. While the characteristics of the 2.37 mu m devices are much improved by the suppression of the CHSH Auger process, since its spin-orbit splitting energy is greater than its band gap, other important Auger processes such as CHHL and CHCC persist. In the larger band gap 2.11 mu m devices, an increase in threshold current with pressure is observed suggesting that CHSH Auger is present in these devices at atmospheric pressure and contributes to performance degradation at these shorter wavelengths.
Murdin BN, Adams AR, Sweeney SJ (2006) Band structure and high-pressure measurements, Springer Series in Optical Sciences 118 pp. 93-127
Determination of the electronic energy vs momentum relationship in semiconductors is essential for the prediction of almost all of their properties. In materials useful for mid-infrared applications, the simplest parabolic band approximations are usually insufficient. However relatively straight-forward numerical techniques based on the k.p method can yield good predictions for the bandstructure. The theoretical bandstructures can be compared with experiment using magneto-optics and magneto-transport, but one of the most useful tools for controllably tuning the system is hydrostatic stress. The strain modifies the bandstructure in a rather s imple way, principally by a linear increase in the fundamental gap, and thus it can be used to separate out effects that depend on bandgap. A large literature has built up on the study of near-infrared optoelectronic devices under pressure. These have been used to establish the variations of the radiative and non-radiative Auger recombination processes with band structure. The results predict that III-V mid-IR lasers with direct band gaps less than the spin-orbit gap should have threshold current densities less than the near-IR lasers based on InP or GaAs. These predictions are found to be consistent with the threshold current density and its variation with pressure observed in InGaAsSb/AlGaAsSb operating at 2.37¼m at atmospheric pressure. Clearly high-pressure techniques provide exciting opportunities for the study of mid-infrared devices. © 2006 Springer-Verlag London Limited.
Zawadzki W, Pfeffer P, Bratschitsch R, Chen Z, Cundiff ST, Murdin BN, Pidgeon CR (2008) Temperature dependence of the electron spin g factor in GaAs, PHYSICAL REVIEW B 78 (24) ARTN 245203 AMER PHYSICAL SOC
Rauter P, Fromherz T, Vinh NQ, Murdin BN, Phillips JP, Pidgeon CR, Diehl L, Dehlinger G, Gruetzmacher D, Zhao M, Ni W-X, Bauer G (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, NEW JOURNAL OF PHYSICS 9 ARTN 128 IOP PUBLISHING LTD
Litvinenko K, Leontiadou M, Li J, Bowyer E, Clowes S, Pidgeon CR, Murdin B (2011) Manipulation of spin dynamics in semiconductor structures by orientation of small external magnetic field, AIP Conference Proceedings 1399 pp. 657-658 American Institute of Physics
Electron spin relaxation times have been measured in InSb and InAs quantum wells and epi-layers in a moderate (
Lynch SA, Greenland PT, Vinh NQ, Litvinenko K, Redlich B, van der Meer L, Warner M, Stoneham AM, Aeppli G, Pidgeon CR, Murdin BN (2008) Lifetime Measurements of Group V Donor Rydberg States in Silicon at THz Frequencies, 2008 5TH IEEE INTERNATIONAL CONFERENCE ON GROUP IV PHOTONICS pp. 24-26 IEEE
Bowyer ET, Villis BJ, Li J, Litvinenko KL, Murdin BN, Erfani M, Matmon G, Aeppli G, Ortega JM, Prazeres R, Dong L, Yu X (2014) Picosecond dynamics of a silicon donor based terahertz detector device, Applied Physics Letters 105 (2)
We report the characteristics of a simple complementary metal-oxide-semiconductor compatible terahertz detector device with low response time (nanoseconds) determined using a short-pulse, high intensity free-electron laser. The noise equivalent power was 1 × 10-11 W Hz -1/2. The detector has an enhanced response over narrow bands, most notably at 9.5 THz, with a continuum response at higher frequencies. Using such a device, the dynamics of donors in silicon can be explored, a system which has great potential for quantum information processing. © 2014 AIP Publishing LLC.
Saeedi K, Szech M, Dluhy P, Salvail JZ, Morse KJ, Riemann H, Abrosimov NV, Nötzel N, Litvinenko KL, Murdin BN, Thewalt ML (2015) Optical pumping and readout of bismuth hyperfine states in silicon for atomic clock applications., Sci Rep 5
The push for a semiconductor-based quantum information technology has renewed interest in the spin states and optical transitions of shallow donors in silicon, including the donor bound exciton transitions in the near-infrared and the Rydberg, or hydrogenic, transitions in the mid-infrared. The deepest group V donor in silicon, bismuth, has a large zero-field ground state hyperfine splitting, comparable to that of rubidium, upon which the now-ubiquitous rubidium atomic clock time standard is based. Here we show that the ground state hyperfine populations of bismuth can be read out using the mid-infrared Rydberg transitions, analogous to the optical readout of the rubidium ground state populations upon which rubidium clock technology is based. We further use these transitions to demonstrate strong population pumping by resonant excitation of the bound exciton transitions, suggesting several possible approaches to a solid-state atomic clock using bismuth in silicon, or eventually in enriched (28)Si.
Hughes MA, Lourenço MA, Carey JD, Murdin B, Homewood KP (2014) Crystal field analysis of Dy and Tm implanted silicon for photonic and quantum technologies, Optics Express 22 (24) pp. 29292-29303
© 2014 Optical Society of America.We report the lattice site and symmetry of optically active Dy3+ and Tm3+ implanted Si. Local symmetry was determined by fitting crystal field parameters (CFPs), corresponding to various common symmetries, to the ground state splitting determined by photoluminescence measurements. These CFP values were then used to calculate the splitting of every J manifold. We find that both Dy and Tm ions are in a Si substitution site with local tetragonal symmetry. Knowledge of rare-earth ion symmetry is important in maximising the number of optically active centres and for quantum technology applications where local symmetry can be used to control decoherence.
Greenland PT, Matmon G, Villis BJ, Bowyer ET, Li J, Murdin BN, van der Meer AFG, Redlich B, Pidgeon CR, Aeppli G (2015) Quantitative analysis of electrically detected Ramsey fringes in P-doped Si, PHYSICAL REVIEW B 92 (16) ARTN 16531 AMER PHYSICAL SOC
Murdin BN (2013) Quantum Computing from the Ground Up, CONTEMPORARY PHYSICS 54 (2) pp. 116-117 TAYLOR & FRANCIS LTD
Vinh NQ, Greenland PT, Litvinenko K, Redlich B, van der Meer AFG, Lynch SA, Warner M, Stoneham AM, Aeppli G, Paul DJ, Pidgeon CR, Murdin BN (2008) Silicon as a model ion trap: Time domain measurements of donor Rydberg states, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 (31) pp. 10649-10653 NATL ACAD SCIENCES
Murdin BN, Litvinenko K, Clarke DG, Pidgeon CR, Murzyn P, Phillips PJ, Carder D, Berden G, Redlich B, van der Meer AF, Clowes S, Harris JJ, Cohen LF, Ashley T, Buckle L (2006) Spin relaxation by transient monopolar and bipolar optical orientation., Phys Rev Lett 96 (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.
O'Brien K, Adams AR, Sweeney SJ, Jin SR, Ahmad CN, Murdin BN, Canedy CL, Vurgaftman I, Meyer JR (2006) Analysis of the major loss processes in mid-infrared type-II "W" diode lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 43-44
The results from high-pressure and low-temperature measurements on mid-infrared type-II W-structure lasers suggest that Auger recombination is the major loss process that prevents their continuous-wave operation at room temperature. © 2006 IEEE.
Murdin BN (2013) Semiconductor Spintronics, CONTEMPORARY PHYSICS 54 (2) pp. 118-119 TAYLOR & FRANCIS LTD
Litvinenko KL, Pavlov SG, Hübers HW, Abrosimov NV, Pidgeon CR, Murdin BN (2014) Photon assisted tunneling in pairs of silicon donors, Physical Review B - Condensed Matter and Materials Physics 89 (23)
Shallow donors in silicon are favorable candidates for the implementation of solid-state quantum computer architectures because of the promising combination of atomiclike coherence properties and scalability from the semiconductor manufacturing industry. Quantum processing schemes require (among other things) controlled information transfer for readout. Here we demonstrate controlled electron tunneling at 10 K from P to Sb impurities and vice versa with the assistance of resonant terahertz photons. © 2014 American Physical Society.
Danilov SN, Wittmann B, Olbrich P, Prettl W, Golub LE, Beregulin EV, Kvon Z-D, Mikhailov NN, Dvoretsky SA, Shalygin VA, Vinh NQ, van der Meer AFG, Murdin B, Ganichev SD (2009) All Electrical Detection of the Stokes Parameters of IR/THz Radiation, 2009 34TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES, VOLS 1 AND 2 pp. 298-299 IEEE
Townsend P, Paul DJ, Lynch SA, Kelsall RW, Ikonic Z, Harrison P, Norris DJ, Cullis AG, Zhang J, Li X, Pidgeon CR, Murdin BN, Murzyn P (2005) LO phonon scattering as a depopulation mechanism in Si/SiGe quantum cascades, 2005 2nd IEEE International Conference on Group IV Photonics pp. 7-9 IEEE
Lynch SA, Thornton Greenland P, Van Der Meer AFG, Murdin BN, Pidgeon CR, Redlich B, Vinh NQ, Aeppli G (2012) Quantum control in silicon using coherent THz pulses, Proceedings of SPIE - The International Society for Optical Engineering 8496
It has long been known that shallow donors such as phosphorous and the other group-V elements, have a hydrogen-like optical spectrum. The main difference is that while the spectrum of atomic hydrogen lies in the visible band, the spectrum of shallow donors in silicon is downshifted to the THz frequency band. This is a direct consequence of the reduced Coulomb attraction seen by the loosely bound electron because the core electrons shield the positive donor atom nucleus, and because the electron is now moving in a dielectric material. While spectroscopy has already revealed much about the energy level structure, very little was known about the temporal dynamics of the system until now. We have used THz pulses from the FELIX free electron laser to probe these hydrogen-like levels. By exploiting the well-known pump-probe technique we have measured the characteristic lifetimes of the excited Rydberg states and found them to be of the order 200 ps. Then, by making subtle changes to the geometry of the pump-probe experimental setup we demonstrate the existence of a THz photon echo. The photon echo is a purely quantum phenomenon with no classical analogue, and it allows us to study the quantum state of the donor electron. We then show, using the photon echo, that it is possible to create a coherent superposition of the ground and excited state of the donor. Measuring the photon echo is important because it can also be used to measure a second important characteristic lifetime of the silicon-donor system, the phase decoherence time. © 2012 SPIE.
Gilbertson AM, Fearn M, Jefferson JH, Murdin BN, Buckle PD, Cohen LF (2008) Zero-field spin splitting and spin lifetime in n-InSb/In1-xAlxSb asymmetric quantum well heterostructures, PHYSICAL REVIEW B 77 (16) ARTN 165335 AMER PHYSICAL SOC
Murdin BN, Litvinenko K, Li J, Bowyer E, Pang M, Greenland PT, Villis B, Aeppli G, van der Meer AFG, Redlich B, Engelkamp H, Pidgeon CR (2015) Nano-orbitronics in silicon, ULTRAFAST MAGNETISM I 159 pp. 92-93 SPRINGER INT PUBLISHING AG
Huebers H-W, Pavlov SG, Lynch SA, Greenland T, Litvinenko KL, Murdin B, Redlich B, van der Meer AFG, Riemann H, Abrosimov NV, Becker P, Pohl H-J, Zhukavin RK, Shastin VN (2013) Isotope effect on the lifetime of the 2p(0) state in phosphorus-doped silicon, PHYSICAL REVIEW B 88 (3) ARTN 035201 AMER PHYSICAL SOC
Jin SR, Ahmad CN, Sweeney SJ, Adams AR, Murdin BN, Page H, Marcadet X, Sirtori C, Tomic S (2006) Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, APPLIED PHYSICS LETTERS 89 (22) ARTN 221105 AMER INST PHYSICS
Rauter P, Fromherz T, Bauer G, Vinh NQ, Phillips PJ, Pidgeon CR, Murdin BN, Diehl L, Dehlinger G, Grützmacher D (2006) Direct measurement of HH2-HH1 intersubband lifetimes in SiGe quantum cascade structures, Third International SiGe Technology and Device Meeting, ISTDM 2006 - Conference Digest 2006
Vinh NQ, Redlich B, van der Meer AFG, Pidgeon CR, Greenland PT, Lynch SA, Aeppli G, Murdin BN (2013) Time-Resolved Dynamics of Shallow Acceptor Transitions in Silicon, PHYSICAL REVIEW X 3 (1) ARTN 011019 AMER PHYSICAL SOC
Litvinenko KL, Nikzad L, Allam J, Murdin BN, Pidgeon CR, Harris JJ, Zhang T, Cohen LF (2007) Spin lifetime in high quality InSb epitaxial layers grown on GaAs, JOURNAL OF APPLIED PHYSICS 101 (8) AMER INST PHYSICS
Pidgeon CR, Litvinenko KL, Nikzad L, Allam J, Cohen LF, Ashley T, Emeny M, Murdin BN (2008) Temperature dependence of the electron Lande g-factor in InSb, NARROW GAP SEMICONDUCTORS 2007 119 pp. 27-29 SPRINGER
Murdin BN (2009) Far-infrared free-electron lasers and their applications, CONTEMPORARY PHYSICS 50 (2) PII 910353824 pp. 391-406 TAYLOR & FRANCIS LTD
Merrick M, Cripps SA, Murdin BN, Hosea TJC, Veal TD, McConville CF, Hopkinson M (2007) Photoluminescence of InNAs alloys: S-shaped temperature dependence and conduction-band nonparabolicity, PHYSICAL REVIEW B 76 (7) ARTN 075209 AMER PHYSICAL SOC
Ganichev SD, Schneider P, Bel'kov VV, Ivchenko EL, Tarasenko SA, Wegscheider W, Weiss D, Schuh D, Murdin BN, Phillips PJ, Pidgeon CR, Clarke DG, Merrick M, Murzyn P, Beregulin EV, Prettl W (2003) Spin-galvanic effect due to optical spin orientation, Physical Review B 68 (8) 081302 pp. --- American Physical Society
Under oblique incidence of circularly polarized infrared radiation the
spin-galvanic effect has been unambiguously observed in (001)-grown $n$-type
GaAs quantum well (QW) structures in the absence of any external magnetic
field. Resonant inter-subband transitions have been obtained making use of the
tunability of the free-electron laser FELIX. It is shown that a helicity
dependent photocurrent along one of the  axes is predominantly
contributed by the spin-galvanic effect while that along the perpendicular
in-plane axis is mainly due to the circular photogalvanic effect. This strong
non-equivalence of the [110] and [1$\bar{1}$0] directions is determined by the
interplay between bulk and structural inversion asymmetries. A microscopic
theory of the spin-galvanic effect for direct inter-subband optical transitions
has been developed being in good agreement with experimental findings.
Leontiadou MA, Litvinenko KL, Gilbertson AM, Pidgeon CR, Branford WR, Cohen LF, Fearn M, Ashley T, Emeny MT, Murdin BN, Clowes SK (2011) Experimental determination of the Rashba coefficient in InSb/InAlSb quantum wells at zero magnetic field and elevated temperatures, JOURNAL OF PHYSICS-CONDENSED MATTER 23 (3) ARTN 035801 IOP PUBLISHING LTD
Litvinenko KL, Bowyer ET, Greenland PT, Stavrias N, Li J, Gwilliam R, Villis BJ, Matmon G, Pang MLY, Redlich B, Van Der Meer AFG, Pidgeon CR, Aeppli G, Murdin BN (2015) Coherent creation and destruction of orbital wavepackets in Si:P with electrical and optical read-out, Nature Communications 6
© 2015 Macmillan Publishers Limited. All rights reserved.The ability to control dynamics of quantum states by optical interference, and subsequent electrical read-out, is crucial for solid state quantum technologies. Ramsey interference has been successfully observed for spins in silicon and nitrogen vacancy centres in diamond, and for orbital motion in InAs quantum dots. Here we demonstrate terahertz optical excitation, manipulation and destruction via Ramsey interference of orbital wavepackets in Si:P with electrical read-out. We show milliradian control over the wavefunction phase for the two-level system formed by the 1s and 2p states. The results have been verified by all-optical echo detection methods, sensitive only to coherent excitations in the sample. The experiments open a route to exploitation of donors in silicon for atom trap physics, with concomitant potential for quantum computing schemes, which rely on orbital superpositions to, for example, gate the magnetic exchange interactions between impurities.
Rauter P, Fromherz T, Vinh NQ, Murdin BN, Mussler G, Gruetzmacher D, Bauer G (2009) Continuous Voltage Tunability of Intersubband Relaxation Times in Coupled SiGe Quantum Well Structures Using Ultrafast Spectroscopy, PHYSICAL REVIEW LETTERS 102 (14) ARTN 147401 AMER PHYSICAL SOC
O'Brien K, Sweeney SJ, Adams AR, Murdin BN, Salhi A, Rouillard Y, Joullie A (2006) Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 mu m, APPLIED PHYSICS LETTERS 89 (5) ARTN 051104 AMER INST PHYSICS
Litvinenko KL, Murdin BN, Allam J, Pidgeon CR, Bird M, Morris K, Branford W, Clowes SK, Cohen LF, Ashley T, Buckle L (2006) Spin relaxation in n-InSb/AlInSb quantum wells, NEW JOURNAL OF PHYSICS 8 PII S1367-2630(06)15617-7 IOP PUBLISHING LTD
Wittmann B, Golub LE, Danilov SN, Karch J, Reitmaier C, Kvon ZD, Vinh NQ, van der Meer AFG, Murdin B, Ganichev SD (2008) Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions, PHYSICAL REVIEW B 78 (20) ARTN 205435 AMER PHYSICAL SOC
Weber W, Golub LE, Danilov SN, Karch J, Reitmaier C, Wittmann B, Bel'kov VV, Ivchenko EL, Kvon ZD, Vinh NQ, van der Meer AFG, Murdin B, Ganichev SD (2008) Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures, PHYSICAL REVIEW B 77 (24) ARTN 245304 AMER PHYSICAL SOC
Stavrias N, Saeedi K, Redlich B, Greenland PT, Riemann H, Abrosimov NV, Thewalt MLW, Pidgeon CR, Murdin Benedict (2017) Competition between homogeneous and inhomogeneous
broadening of orbital transitions in Si:Bi,
Physical Review B 96 (15) 155204 pp. 1-8 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
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.
Litvinenko KL, Leontiadou MA, Li J, Bowyer ET, Clowes SK, Pidgeon CR, Murdin BN (2011) Manipulation of spin dynamics in semiconductor structures by orientation of small external magnetic field, AIP Conference Proceedings 1399 pp. 657-658
We have investigated the effect of an external magnetic field on the electron spin lifetime in narrow gap semiconductors (NGS). In zero field, we show that the D'yakonov-Perel process dominates even at low temperatures. In the Faraday configuration it is suppressed and the spin lifetime increases with field, whereas in Voigt configuration, the additional Margulis-Margulis process, which is particularly effective in NGS, shortens the spin lifetime considerably. The spin dynamics are found to be very sensitive to both the magnitude and direction of the magnetic field. © 2011 American Institute of Physics.
Green RP, Tredicucci A, Vinh NQ, Murdin B, Pidgeon C, Beere HE, Ritchie DA (2009) Gain recovery dynamics of a terahertz quantum cascade laser, PHYSICAL REVIEW B 80 (7) ARTN 075303 AMER PHYSICAL SOC
Lynch SA, Greenland PT, van der Meer AFG, Murdin BN, Pidgeon CR, Redlich B, Nguyen QV, Aeppli G (2010) First Observation of a THz Photon Echo, 35TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ 2010) IEEE
Jefferson PH, Veal TD, Piper LFJ, Bennett BR, McConville CF, Murdin BN, Buckle L, Smith GW, Ashley T (2006) Band anticrossing in GaNxSb1-x, APPLIED PHYSICS LETTERS 89 (11) ARTN 111921 AMER INST PHYSICS
Litvinenko KL, Nikzad L, Pidgeon CR, Allam J, Cohen LF, Ashley T, Emeny M, Zawadzki W, Murdin BN (2008) Temperature dependence of the electron Lande g factor in InSb and GaAs, PHYSICAL REVIEW B 77 (3) ARTN 033204 AMER PHYSICAL SOC
Litvinenko Konstantin, Greenland PT, Redlich B, Pidgeon CR, Aeppli G, Murdin Benedict (2016) Weak probe readout of coherent impurity orbital superpositions in silicon, Physical Review B - Condensed Matter and Materials Physics 94 (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.
Andreev Y, Kokh A, Kokh K, Lanskii G, Litvinenko K, Mamrashev A, Molloy J, Murdin B, Naftaly M, Nikolaev N, Svetlichnyi V (2017) Observation of a different birefringence order at optical and THz frequencies in LBO crystal, Optical Materials 66 pp. 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
Chick Steven, Stavrias N., Saeedi K., Redlich B., Greenland P. T., Matmon G., Naftaly M., Pidgeon C. R., Aeppli G., Murdin Benedict (2017) Coherent superpositions of three states for phosphorous donors in silicon prepared using THz radiation, Nature Communications 8 16038 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.
Litvinenko Konstantin, Li Juerong, Stavrias N, Meaney A, Christianen P, Engelkamp H, Homewood Kevin, Pidgeon C, Murdin Benedict (2016) The Quadratic Zeeman effect used for state-radius determination in neutral donors and donor bound excitons in Si:P, Semiconductor Science and Technology 31 045007 pp. 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.
van Loon M, Stavrias Nikolaos, Le N, Litvinenko Konstantin, Greenland P, Pidgeon C, Saeedi K, Redlich B, Aeppli G, Murdin Benedict (2018) Giant multiphoton absorption for THz resonances in silicon hydrogenic donors, Nature Photonics 12 pp. 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.
Saeedi K., Stavrias N., Redlich B., Riemann H., Abrosimov N.V., Becker P., Pohl H-J., Thewalt M.L.W., Murdin Benedict (2018) Short lifetime components in the relaxation of boron acceptors in silicon, Physical Review B 97 (12) 125205 pp. 125205-1 - 125205-6 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
Wu W, Greenland P, Fisher A, Le Huy Nguyen, Chick Steven, Murdin Benedict (2018) Excited states of defect linear arrays in silicon: A first-principles study based on
hydrogen cluster analogues,
Physical Review B 97 (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.
Matmon G, Ginossar E, Villis B, Kolker A, Lim T, Solanki H, Schofield S, Curson N, Li J, Murdin B, Fisher A, Aeppli G (2018) 2D-3D crossover in a dense electron liquid in silicon, Physical Review B 97 155306 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.
Veal T. D., Piper L. F. J., Jefferson P. H., Mahboob I., McConville C. F., Merrick M., Hosea T. J. C., Murdin B. N., Hopkinson M. (2005) Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys, Applied Physics Letters 182114 (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.

Merrick M., Cripps S. A., Murdin B. N., Hosea T.J. C., Veal T. D., McConville C. F., Hopkinson M. (2007) Photoluminescence of InNAs alloys: S-shaped temperature dependence and conduction-band nonparabolicity, Physical Review B 76 (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.

Litvinenko K L, Nikzad L, Allam J, Murdin B N, Pidgeon C R, Harris J J, Zhang T, Cohen L F (2007) Spin Lifetime in High Quality InSb Epitaxial Layers Grown on GaAs, Journal of Applied Physics 101 (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.

Pidgeon C. R., Murzyn P., Wells J.-P. R., Gordon N. T., Ashley T., Jefferson J. H., Burke T. M., Maxey C. D., Murdin B. N. (2002) Electron spin coherence in long wavelength Hg 1-xCd xTe, pp. 25-26
Murdin B. N., Litvinenko K., Clarke D. G., Pidgeon C. R., Murzyn P., Phillips P. J., Carder D., Berden G., Redlich B., van der Meer A. F. G., Clowes S., Harris J. J., Cohen L. F., Ashley T., Buckle L. (2006) Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, Physical Review Letters 96 (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.

Veal T D, Piper L F, Jollands S, Bennett B R, Jefferson P H, Thomas P A, McConville C F, Murdin B N, Buckle L, Smith G W, Ashley T (2005) Band Gap Reduction in GaNSb Alloys Due to the Anion Mismatch, Applied Physics Letters 87 (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.

Jin S. R., Sweeney S. J., Ahmad C. N., Adams A. R., Murdin B. N. (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, Applied Physics Letters 357 (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

Litvinenko K L, Murdin B N, Allam J, Pidgeon C R, Zhang T, Harris J J, Cohen L F, Eustace D A, McComb D W (2006) Spin Lifetime in InAs Epitaxial Layers Grown on GaAs, Physical Review B 74 (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.

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.

Litvinenko K. L., Murdin B. N., Allam J., Pidgeon C. R., Bird M., Morris K., Branford W., Clowes S. K., Cohen L. F., Ashley T., Buckle L. (2006) Spin relaxation in n-InSb/AlInSb quantum wells, New Journal of Physics 8 (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.

Litvinenko K. L., Nikzad L., Allam J., Murdin B. N., Pidgeon C. R., Harris J. J., Zhang T., Cohen L. F. (2007) Spin lifetime in high quality InSb epitaxial layers grown on GaAs, Journal of Applied Physics 083105 (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.

Rauter P., Fromherz T., Bauer G., Vinh N. Q., Murdin B. N., Phillips J. P., Pidgeon C. R., Diehl L., Dehlinger G., Grützmacher D. (2006) Direct monitoring of the excited state population in biased SiGe valence band quantum wells by femtosecond resolved photocurrent experiments, Applied Physics Letters 211111 (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.

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.

Murzyn P., Pidgeon C. R., Phillips P. J., Merrick M., Litvinenko K. L., Allam J., Murdin B. N., Ashley T., Jefferson J. H., Miller A., Cohen L. F. (2003) Suppression of D'yakonov?Perel spin relaxation in InAs and InSb by n-type doping at 300 K, Applied Physics Letters 5220 (2003)
Roither J., Pichler S., Kovalenko M. V., Heiss W., Feychuk P., Panchuk O., Allam J., Murdin B. N. (2006) Two- and one-dimensional light propagations and gain in layer-by-layer-deposited colloidal nanocrystal waveguides, Applied Physics Letters 111120 (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.

Roither J, Pichler S, Kovalenko M V, Heiss W, Feychuk P, Panchuck O, Allam J, Murdin B N (2006) Two- and One-Dimensional Light Propagations and Gain in Layer-by-Layer-Deposited Colloidal Nanocrystal Waveguides, Applied Physics Letters 89 (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.

Litvinenko K L, Murdin B N, Allam J, Pidgeon C R, Bird M, Morris K, Branford W, Clowes S K, Cohen L F, Ashley T, Buckle L (2006) Spin Relaxation in N-InSb/AlInSb Quantum Wells, New Journal of Physics 8 (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).

Rauter P, Fromherz T, Bauer G, Vinh N Q, Murdin B N, Phillips J P, Pidgeon C R, Diehl L, Dehlinger G, Grutzmacher D (2006) Direct Monitoring of the Excited State Population in Biased SiGe Valence Band Quantum Wells by Femtosecond Resolved Photocurrent Experiments, Applied Physics Letters 89 (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.

Merrick M, Cripps S A, Murdin B N, Hosea T J, Veal T D, McConville C F, Hopkinson M (2007) Photoluminescence of InNAs alloys: S-Shaped Temperature Dependence and Conduction-Band Nonparabolicity, Physical Review B 76 (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.

Dent C. J., Murdin B. N., Galbraith I. (2003) Phase and intensity dependence of the dynamical Franz-Keldysh effect, Physical Review B 67 (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.

Veal T. D., Piper L. F. J., Jollands S., Bennett B. R., Jefferson P. H., Thomas P. A., McConville C. F., Murdin B. N., Buckle L., Smith G. W., Ashley T. (2005) Band gap reduction in GaNSb alloys due to the anion mismatch, Applied Physics Letters 132101 (2005)

The structural and optoelectronic properties in GaNxSb1?x alloys
(0dxxSb1?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.

Rauter P., Fromherz T., Bauer G., Vinh N. Q., Phillips P. J., Pidgeon C. R., Murdin B. N., Diehl L., Dehlinger G., Grutzmacher D. (2006) Direct Measurement of HH2-HH1 Intersubband Lifetimes in SiGe Quantum Cascade Structures, pp. 1-2
Gilbertson A M, Fearn M, Jefferson J H, Murdin B N, Buckle P D, Cohen L F (2008) Zero-Field Spin Splitting and Spin Lifetime in n-InSb/In1-xAlxSb Asymmetric Quantum Well Heterostructures, Physical Review B 77 (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.

O'Brien K., Sweeney S. J., Adams A. R., Murdin B. N, Salhi A., Rouillard Y., Joullié A. (2006) Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 µm, Applied Physics Letters 051104 (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.

Murdin B N, Litvinenko K, Clarke D G, Pidgeon C R, Murzyn P, Phillips P J, Carder D, Berden G, Redlich B, van der Meer A F, Clowes S, Harris J J, Cohen L F, Ashley T, Buckle L (2006) Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, Physical Review Letters 96 (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.

Murdin B. N., Litvinenko K., Allam J., Pidgeon C. R., Bird M., Morrison K., Zhang T., Clowes S. K., Branford W. R., Harris J., Cohen L. F. (2005) Temperature and doping dependence of spin relaxation in n-InAs, Physical Review B 72 (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.

Jin S. R., Ahmad C. N., Sweeney S. J., Adams A. R., Murdin B. N., Page H., Marcadet X., Sirtori C., Tomi? S. (2006) Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, Applied Physics Letters 221105 (2006)
Lynch Stephen A., Paul Douglas J., Townsend Paul, Matmon Guy, Suet Zhang, Kelsall Robert W., Ikonic Zoran, Harrison Paul, Zhang Jing, Norris David J., Cullis Anthony G., Pidgeon Carl R., Murzyn Pawel, Murdin Ben, Bain Mike, Gamble Harry S., Zhao Ming, Ni Wei-Xin (2006) Toward Silicon-Based Lasers for Terahertz Sources, IEEE Journal of Selected Topics in Quantum Electronics 12 (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

Gilbertson A. M., Fearn M., Jefferson J. H., Murdin B. N., Buckle P. D., Cohen L. F. (2008) Zero-field spin splitting and spin lifetime in n-InSb/In1?xAlxSb asymmetric quantum well heterostructures, Physical Review B 77 (165335)
Rauter P, Fromherz T, Vinh N Q, Murdin B N, Phillips J P, Pidgeon C R, Diehl L, Dehlinger G, Grutzmacher D, Zhao M, Ni W X, Bauer G (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, New Journal of Physics 9 (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.

Murdin B N, Litvinenko K, Allam J, Pidgeon C R, Bird M, Morrison K, Zhang T, Clowes S K, Branford W R, Harris J, Cohen L F (2005) Temperature and Doping Dependence of Spin Relaxation in n-InAs, Physical Review B 72 (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.

Califano M, Vinh N Q, Phillips P J, Ikonic Z, Kelsall R W, Harrison P, Pidgeon C R, Murdin B N, Paul D J, Townsend P, Zhang J, Ross I M, Cullis A G (2007) Interwell Relaxation Times in p-Si/SiGe Asymmetric Quantum Well Structures: Role of Interface Roughness, Physical Review B 75 (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.

Murzyn P, Pidgeon C R, Phillips P J, Merrick M, Litvinenko K L, Allam J, Murdin B N, Ashley T, Jefferson J H, Miller A, Cohen L F (2003) Suppression of D'yakonov-Perel Spin Relaxation in InAs and InSb by n-Type Doping at 300 K, Applied Physics Letters 83 (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.

Litvinenko K. L., Murdin B. N., Allam J., Pidgeon C. R., Zhang T., Harris J. J., Cohen L. F., Eustace D. A., McComb D. W. (2006) Spin lifetime in InAs epitaxial layers grown on GaAs, Physical Review B 74 (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.

Rauter P., Fromherz T., Vinh N. Q., Murdin B. N., Phillips J. P., Pidgeon C. R., Diehl L., Dehlinger G., Grützmacher D., Zhao Ming, Ni Wei-Xin, Bauer G. (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, New Journal of Physics 9 (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 ¼m) 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.

Califano Marco, Vinh N. Q., Phillips P. J., Ikoni? Z., Kelsall R. W., Harrison P., Pidgeon C. R., Murdin B. N., Paul D. J., Townsend P., Zhang J., Ross I. M., Cullis A.G. (2007) Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: Role of interface roughness, Physical Review B 75 (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.

Weber W, Golub L E, Danilov S N, Karch J, Reitmaier C, Wittmann B, Bel'kov W, Ivchenko E L, Kvon Z D, Vinh N Q, van der Meer A F, Murdin B, Ganichev S D (2008) Quantum Ratchet Effects Induced by Terahertz Radiation in GaN-Based Two-Dimensional Structures, Physical Review B 77 (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.

Pidgeon C. R., Murzyn P., Wells J.-P. R., Gordon N. T., Ashley T., Jefferson J. H., Burke T. M., Maxey C. D., Murdin B. N. (2002) Electron spin coherence in long wavelength Hg 1-xCd xTe, pp. 25-26
Jin S R, Ahmad C N, Sweeney S J, Adams A R, Murdin B N, Page H, Marcadet X, Sirtori C, Tomic S (2006) Spectroscopy of GaAs/AlGaAs Quantum-Cascade Lasers Using Hydrostatic Pressure, Applied Physics Letters 89 (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.

Veal T D, Piper L F, Jefferson P H, Mahboob I, McConville C F, Merrick M, Hosea T J, Murdin B N, Hopkinson M (2005) Photoluminescence Spectroscopy of Bandgap Reduction in Dilute InNAs Alloys, Applied Physics Letters 87 (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.

O'Brien K, Sweeney S J, Adams A R, Murdin B N, Salhi A, Rouillard Y, Joullie A (2006) Recombination Processes in Midinfrared InGaAsSb Diode Lasers Emitting at 2.37 mu m, Applied Physics Letters 89 (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.

Lynch S A, Paul D J, Townsend P, Matmon G, Suet Z, Kelsall R W, Ikonic Z, Harrison P, Zhang J, Norris D J, Culllis A G, Pidgeon C R, Murzyn P, Murdin B, Bain M, Gamble H S, Zhao M, Ni W X (2006) Toward Silicon-Based Lasers for Terahertz Sources, IEEE Journal of Selected Topics in Quantum Electronics 12 (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.

Li Juerong, Le Nguyen H., Litvinenko K., Clowes S. K., Engelkamp H., Pavlov S. G., Hübers H. -W. ., Shuman V. B., Portsel L. M., Lodygin A. N., Astrov A., Abrosimov N. V., Pidgeon C. R., Fisher A., Zeng Zaiping, Niquet Y. -M., Murdin B. N. (2018) Radii of Rydberg states of isolated silicon donors, Physical Review B 98 085423 pp. 085423-1 - 085423-8 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.
Peach Tomas, Homewood Kevin, Lourenco Manon, Hughes M, Saeedi Kaymar, Stavrias Nikolaos, Li Juerong, Chick Steven, Murdin Benedict, Clowes Steven (2018) The Effect of Lattice Damage and Annealing Conditions on the Hyperfine Structure of Ion Implanted Bismuth Donors in Silicon, Advanced Quantum Technologies 1 (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.
Chick Steven, Murdin B N, Matmon Guy, Naftaly Mira (2018) Metrology of complex refractive index for solids in the terahertz regime using frequency domain spectroscopy, Metrologia 55 (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.
Nguyen H. Le, Lanskii Grigory V., Aeppli G. Aeppli, Murdin B.N. Murdin (2019) Giant non-linear susceptibility of hydrogenic donors in silicon and germanium, Light: Science & Applications 8 64 pp. 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)Dn3D = 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.
Saeedi Kamyar, Stavrias Nikolas, Redlich Britta, van der Meer A.F.G., Mikhaylovskiy Rostislav, Kimel Alexey V, Pidgeon C R, Murdin B N (2019) Spin preservation during THz orbital pumping of shallow donors in silicon, 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.
Peach T., Stockbridge K., Li Juerong, Homewood K. P., Lourenco M. A., Chick S., Hughes M. A., Murdin B. N., Clowes S. K. (2019) Enhanced diffusion and bound exciton interactions of high density implanted bismuth donors in silicon, Applied Physics Letters 115 (7) 072102 pp. 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.
Stockbridge Kristian, Chick Steven, Crane E., Fisher A., Murdin Benedict (2020) Using non-homogeneous point process statistics to find multi-species
event clusters in an implanted semiconductor,
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.
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.
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.