The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of
Tan SL, Soong WM, Green JE, Steer MJ, Zhang S, Tan LJJ, Ng JS, Marko IP, Sweeney SJ, Adams AR, Allam J, David JPR (2013) Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes,Applied Physics Letters 103 (10)
The anomalous behavior of impact ionization in dilute-nitride GaInNAs photodiodes with a range of nitrogen content below 4% is investigated. The ratio of hole- and electron-initiated ionization coefficients, k = ²/±, is enhanced by a factor up to
Marko IP, Andreev AD, Adams AR, Krebs R, Reithmaier JP, Forchel A (2003) Importance of Auger recombination in InAs 1.3 mu m quantum dot lasers, ELECTRONICS LETTERS 39 (1) pp. 58-59 IEE-INST ELEC ENG
Sweeney SJ, Marko IP, Jin SR, Hild K, Batool Z, Ludewig P, Natterman L, Bushell Z, Stolz W, Volz K, Broderick CA, Usman M, Harnedy PE, O'Reilly EP, Butkute R, Pacebutas V, Geizutis A, Krotkus A (2014) Electrically injected GaAsBi Quantum Well Lasers, 2014 24TH IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2014) pp. 80-81 IEEE COMPUTER SOC
GaAsBi QWs have the potential to remove inherent recombination losses thereby
increasing the efficiency and reducing the temperature sensitivity of near-infrared
telecommunications lasers. GaAsBi QW lasers are reported and prospects for 1550nm
operation are discussed.
Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10?15 cm?1 and a peak modal gain of 24 cm?1, corresponding to a material gain of approximately 1500 cm?1 at a current density of 2 kA cm?2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared.
Sweeney SJ, Hild K, Marko IP, Yu S-Q, Johnson SR, Zhang Y-H (2008) Thermal characteristics of 1.3 mu m GaAsSb/GaAs-based Edge- and Surface-emitting Lasers, 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE pp. 83-84 IEEE
Aldukhayel A, Jin SR, Marko IP, Sweeney SJ, Zhang SY, Revin DG, Cockburn JW (2013) Investigations of carrier scattering into L-valley in »=3.5¼m InGaAs/AlAs(Sb) quantum cascade lasers using high hydrostatic pressure, Physica Status Solidi (B) Basic Research 250 (4) pp. 693-697
In order to identify the performance limitations of InGaAs/AlAs(Sb) quantum cascade lasers, experimental investigations of the temperature and pressure dependencies of the threshold current (I) were undertaken. Using the theoretical optical phonon current (I) and carrier leakage (I) to fit the measured threshold current at various pressures, we show that the electron scattering from the top lasing level to the upper L-minima gives rise to the increase in I with pressure and temperature. It was found that this carrier leakage path accounts for approximately 3% of I at RT and is negligible at 100K. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Marko IP, Adams AR, Sweeney SJ, Teissier R, Baranov AN, Tomic S (2009) Evidence of carrier leakage into the L-valley in InAs-based quantum cascade lasers under high hydrostatic pressure, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (3) pp. 512-515 WILEY-V C H VERLAG GMBH
Marko IP, Andreev AD, Adams AR, Krebs R, Reithmaier JP, Forchel A (2003) Auger recombination in 1.3-¼m InAs/GaInAs quantum dot lasers studied using high pressure, Conference on Lasers and Electro-Optics Europe - Technical Digest pp. 175-175
The Auger recombination in 1.3¼m InAs/GalnAs quantum dot lasers were investigated. To analyse the experimental results, theoretical model was used which includes strain, piezoelectric field and electronic structure calculated in the QDs of truncated pyramid shape. It was found that the radiative current increases with pressure, but the Auger recombination current decreases with pressure and is the dominant recombination path at room temperature in 1.3¼m QD lasers. © 2003 IEEE.
Lever L, Hu Y, Myronov M, Liu X, Owens N, Gardes FY, Marko IP, Sweeney SJ, Ikonic Z, Leadley DR, Reed GT, Kelsall RW (2011) Modulation of the absorption coefficient at 1.3 mu m in Ge/SiGe multiple quantum well heterostructures on silicon,OPTICS LETTERS 36 (21) pp. 4158-4160
We report modulation of the absorption coefficient at 1.3 ¼m in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew 9 nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range 1290?1315 nm.
Ikyo BA, Marko IP, Hild K, Adams AR, Sweeney SJ, Arafin S, Amann M-C (2013) The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers, Lasers and Electro-Optics Europe (CLEO EUROPE/IQEC), 2013 Conference on and International Quantum Electronics Conference IEEE
Tan SL, Hunter CJ, Zhang S, Tan LJJ, Goh YL, Ng JS, David JPR, Marko IP, Sweeney SJ, Adams AR, Allam J (2012) Improved Optoelectronic Properties of Rapid Thermally Annealed Dilute Nitride GaInNAs Photodetectors, Journal of Electronic Materials pp. 1-9
We investigate the optical and electrical characteristics of GaInNAs/GaAs long-wavelength photodiodes grown under varying conditions by molecular beam epitaxy and subjected to postgrowth rapid thermal annealing (RTA) at a series of temperatures. It is found that the device performance of the nonoptimally grown GaInNAs p
structures, with nominal compositions of 10% In and 3.8% N, can be improved significantly by the RTA treatment to match that of optimally grown structures. The optimally annealed devices exhibit overall improvement in optical and electrical characteristics, including increased photoluminescence brightness, reduced density of deep-level traps, reduced series resistance resulting from the GaAs/GaInNAs heterointerface, lower dark current, and significantly lower background doping density, all of which can be attributed to the reduced structural disorder in the GaInNAs alloy. © 2012 TMS.
Hild K, Batool Z, Jin SR, Hossain N, Marko IP, Hosea TJC, Lu X, Tiedje T, Sweeney SJ (2013) Auger Recombination Suppression And Band Alignment In GaAsBi/GaAs Heterostructures, PHYSICS OF SEMICONDUCTORS 1566 pp. 488-489 AMER INST PHYSICS
Using a combination of experimental and theoretical techniques we present the dependence of the bandgap
Eg and the spin orbit splitting energy so, with Bi concentration in GaAsBi/GaAs samples. We find that the
concentration at which so,> Eg occurs at 9%. Both spectroscopic as well as first device results indicate a type I alignment.
Semiconductor lasers with quantum dot (QD) based active regions have generated a huge amount of interest for applications including communications networks due to their anticipated superior physical properties due to three dimensional carrier confinement. For example, the threshold current of ideal quantum dots is predicted to be temperature insensitive. We have investigated the operating characteristics of 1.55 ¼m InAs/InP (100) quantum dot lasers focusing on their carrier recombination characteristics using a combination of low temperature and high pressure measurements. By measuring the intrinsic spontaneous emission from a window fabricated in the n-contact of the devices we have measured the radiative component of the threshold current density, Jrad. We find that Jrad is itself relatively temperature insensitive (Fig. 1). However, the total threshold current density, Jth, increases significantly with temperature leading to a characteristic temperature T0~72 K around 220 K-290 K. From this data it is clear that the devices are dominated by a non-radiative recombination process which accounts for up to 94% of the threshold current at room temperature (Fig. 1).
Pal J, Migliorato MA, Li C-K, Wu Y-R, Crutchley BG, Marko IP, Sweeney SJ (2013) Enhancement of efficiency of InGaN-based light emitting diodes through strain and piezoelectric field management, Journal of Applied Physics 114 (7)
We report calculations of the strain dependence of the piezoelectric field within InGaN multi-quantum wells light emitting diodes. Such fields are well known to be a strong limiting factor of the device performance. By taking into account the nonlinear piezoelectric coefficients, which in particular cases predict opposite trends compared to the commonly used linear coefficients, a significant improvement of the spontaneous emission rate can be achieved as a result of a reduction of the internal field. We propose that such reduction of the field can be obtained by including a metamorphic InGaN layer below the multiple quantum well active region. © 2013 AIP Publishing LLC.
Fehse R, Marko I, Adams AR (2003) Long wavelength lasers on GaAs substrates, IEE PROCEEDINGS-CIRCUITS DEVICES AND SYSTEMS 150 (6) pp. 521-528 IEE-INST ELEC ENG
Ikyo AB, Marko IP, Adams AR, Sweeney SJ, Bachmann A, Kashani-Shirazi K, Amann M-C (2009) Gain peak-cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure, IET OPTOELECTRONICS 3 (6) pp. 305-309 INST ENGINEERING TECHNOLOGY-IET
Marko IP, Jin SR, Hild K, Batool Z, Bushell ZL, Ludewig P, Stolz W, Volz K, Butkute R, Pacebutas V, Geizutis A, Krotkus A, Sweeney SJ (2015) Properties of hybrid MOVPE/MBE grown GaAsBi/GaAs based near-infrared emitting quantum well lasers, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 094008 IOP PUBLISHING LTD
We have investigated the threshold current Ith and differential quantum efficiency as the function of temperature in InGaAlAs/InP multiple quantum well (MQWs) buried heterostructure (BH) lasers. We find that the temperature sensitivity of Ith is due to non-radiative recombination which accounts for up to ~80% of Jth at room temperature. Analysis of spontaneous emission emitted from the devices show that the dominant non-radiative recombination process is consistent with Auger recombination. We further show that the above threshold differential internal quantum efficiency, ·i, is ~80% at 20°C remaining stable up to 80°C. In contrast, the internal optical loss, ±i, increases from 15 cm-1 at 20°C to 22 cm-1 at 80°C, consistent with inter-valence band absorption (IVBA). This suggests that the decrease in power output at elevated temperatures is associated with both Auger recombination and IVBA.
Crutchley BG, Marko IP, Adams AR, Sweeney SJ (2013) Investigating the efficiency limitations of GaN-based emitters, Optics InfoBase Conference Papers
Crutchley BG, Marko IP, Adams AR, Sweeney SJ (2010) Efficiency limitations of green InGaN LEDs and laser diodes, 22nd IEEE International Semiconductor Laser Conference pp. 27-28
Tan LJJ, Soong WS, Tan SL, Goh YL, Steer MJ, Ng JS, David JPR, Marko IP, Chamings J, Allam J, Sweeney SJ, Adams AR (2009) Dark current mechanisms in InxGa1-xAs 1-yNy, IEEE Proceedings of LEOS Annual Meeting Conference pp. 233-234 IEEE
In order to extend the photo response of GaAs to optical telecommunication wavelengths, In and N can be incorporated into GaAs to yield a perfect lattice match of InxGa1-xAs1-yNy with GaAs with a bandgap that strongly decreases with increasing N composition. The potential usage of such a material as photodetectors and photovoltaic applications has been reported.In this work, we investigate the dark current mechanisms in the InxGa1-xAs1-yNy material.
Tan SL, Zhang S, Soong WM, Goh YL, Tan LJJ, Ng JS, David JPR, Marko IP, Adams AR, Sweeney SJ, Allam J (2011) GaInNAsSb/GaAs Photodiodes for Long-Wavelength Applications, IEEE ELECTRON DEVICE LETTERS 32 (7) pp. 919-921 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Crowley MT, Marko IP, Masse NF, Andreev AD, Sweeney SJ, O'Reilly EP, Adams AR (2008) The importance of recombination via excited states in InAs/GaAs 1.3¼m quantum dot lasers, IEEE Proceedings of 21st International Semiconductor Laser Conference pp. 117-118 IEEE
The optical matrix element for excited-states is significantly weaker than the ground-state leading to thermally stable radiative recombination. This is not so for non-radiative Auger recombination, causing a sharp increase in threshold current with temperature.
Crutchley BG, Marko IP, Sweeney SJ (2013) The influence of temperature on the recombination processes in blue and green InGaN LEDs, Physica Status Solidi (C) Current Topics in Solid State Physics 2 (12)
A temperature dependent investigation into the efficiency droop effect in blue and green InGaN light-emitting diodes (LEDs) is presented. The efficiency droop effect is observed to be the strongest at low temperatures in both blue and green LEDs. We show such behaviour is consistent with a reduced hole injection rate resulting in an increased concentration of electron leakage from the quantum wells. Spectral measurements demonstrate that the emission peak has an "s-shape" dependence on tem-perature and a full-width at half-maximum which increases with decreasing temperature below 100 K. Such observations indicate the importance of carrier localization in the InGaN LEDs. At temperatures where hole injection is not problematic the efficiency droop is the result of carrier delocalization and subsequent defect related recombination with increasing current injection. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hild K, Sweeney SJ, Wright S, Lock DA, Jin SR, Marko IP, Johnson SR, Chaparro SA, Yu S-Q, Zhang Y-H (2006) Carrier recombination in 1.3 mu m GaAsSb/GaAs quantum well lasers,APPLIED PHYSICS LETTERS 89 (17) ARTN 173509
AMER INST PHYSICS
Marko IP, Andreev AD, Adams AR, Krebs R, Reithmaier JP, Forchel A (2003) High-pressure studies of the recombination processes, threshold currents, and lasing wavelengths in InAs/GaInAs quantum dot lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 235 (2) pp. 407-411 WILEY-V C H VERLAG GMBH
Hild K, Sweeney SJ, Marko IP, Jin SR, Johnson SR, Chaparro SA, Yu S, Zhang Y-H (2007) Temperature and pressure dependence of carrier recombination processes in GaAsSb/GaAs quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 197-202 WILEY-V C H VERLAG GMBH
Blume G, Hild K, Marko IP, Hosea TJC, Yu SQ, Chaparro SA, Samal N, Johnson SR, Zhang YH, Sweeney SJ (2012) Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements,Journal of Applied Physics 112 (3)
We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 ¼m target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs. © 2012 American Institute of Physics.
Marko IP, Ikyo AB, Adams AR, Sweeney SJ, Bachmann A, Kashani-Shirazi K, Amann M-C (2009) Band-structure and gain-cavity tuning of 2.4-¼m GaSb buried tunnel junction VCSELs, Optics InfoBase Conference Papers
Marko I, Masse N, Sweeney S, Adams A, Sellers I, Mowbray D, Skolnick M, Liu H, Groom K (2005) Effect of gain saturation and nonradiative recombination on the thermal characteristics of InAs/GaAs 1.3 mu m quantum dot lasers,The 18th Annual Meeting of the IEEE Lasers and Electro-Optics Society, 2005. (LEOS 2005) pp. 401-402
Gain saturation increases the radiative component, J(rad), of the threshold current density, J(th), and its contribution to the thermal sensitivity of J(th) in short cavity or low QD density devices. However, the main cause of their thermal sensitivity is a strong non-radiative recombination.
Bismuth-containing III-V alloys open-up a range of possibilities for practical applications in semiconductor lasers, photovoltaics, spintronics, photodiodes and thermoelectrics. Of particular promise for the development of semiconductor lasers is the possibility to grow GaAsBi laser structures such that the spin-orbit-splitting energy (SO) is greater than the bandgap (Eg) in the active region for devices operating around the telecom wavelength of 1.55 ¼m, thereby suppressing the dominant efficiency-limiting loss processes in such lasers, namely Auger recombination and inter-valence band absorption (IVBA). The SO > Eg band structure is present in GaAsBi alloys containing > 10% Bi, at which composition the alloy band gap is close to 1.55 ¼m on a GaAs substrate making them an attractive candidate material system for the development of highly efficient, uncooled GaAs-based lasers for telecommunications. Here we discuss progress towards this goal and present a comprehensive set of data on the properties of GaAsBi lasers including optical gain and absorption characteristics and the dominant carrier recombination processes in such systems. Finally, we briefly review the potential of GaAsBiN and InGaAsBi material systems for near- and mid-infrared photonic devices on GaAs and InP platforms, respectively.
The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 ¼m, 2.6 ¼m and 2.9 ¼m, are investigated. Temperature characterization techniques and measurements under hydrostatic pressure identify an Auger process as the dominant non-radiative recombination mechanism in these devices. The results are supplemented with hydrostatic pressure measurements from three additional type-I GaInAsSb lasers, extending the wavelength range under investigation from 1.85-2.90 ¼m. Under hydrostatic pressure, contributions from the CHCC and CHSH Auger mechanisms to the threshold current density can be investigated separately. A simple model is used to fit the non-radiative component of the threshold current density, identifying the dominance of the different Auger losses across the wavelength range of operation. The CHCC mechanism is shown to be the dominant non-radiative process at longer wavelengths (> 2 ¼m). At shorter wavelengths (
Tan S, Hunter C, Zhang S, Tan L, Goh Y, Ng J, David J, Marko I, Sweeney S, Adams AR, Allam J (2012) Improved optoelectronic properties of rapid thermally annealed dilute nitride GaInNAs photodetectors,Journal of Electronic Materials 41 (12) pp. 3393-3401
We investigate the optical and electrical characteristics of GaInNAs/GaAs long-wavelength photodiodes grown under varying conditions by molecular beam epitaxy and subjected to postgrowth rapid thermal annealing (RTA) at a series of temperatures. It is found that the device performance of the nonoptimally grown GaInNAs p-i-n structures, with nominal compositions of 10% In and 3.8% N, can be improved significantly by the RTA treatment to match that of optimally grown structures. The optimally annealed devices exhibit overall improvement in optical and electrical characteristics, including increased photoluminescence brightness, reduced density of deep-level traps, reduced series resistance resulting from the GaAs/GaInNAs heterointerface, lower dark current, and significantly lower background doping density, all of which can be attributed to the reduced structural disorder in the GaInNAs alloy.© 2012 TMS.
In this study low temperature and high pressure techniques have been used to investigate the recombination processes taking place in InGaN-based quantum well light emitting diodes (LEDs) which have emission across the blue-green region. Despite relatively high peak efficiencies of the GaN-based emitters, there remain issues relating to the strong efficiency reduction at higher currents that are required for normal operation in most applications. It is observed that there is a relative reduction in efficiency as injection current is increased in a phenonmenon which is known as efficiency droop. There are three main arguments for the cause of efficiency droop that are discussed in the literature: non-radiative Auger recombination, carrier leakage and a defect-related loss mechanism. In spite of extensive research to date, there is little agreement on the cause of efficiency droop as most experiments can only measure the overall efficiency behaviour leading to difficulties in determining the individual contributions from the different loss mechanisms. © 2013 IEEE.
Broderick CA, Jin S, Marko Igor, Hild Konstanze, Ludewig P, Bushell Zoe, Stolz W, Rorison JM, O?Reilly EP, Volz K, Sweeney Stephen (2017) GaAs1?xBix/GaNyAs1?y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics,Scientific Reports 7 46371
Nature Publishing Group
The potential to extend the emission wavelength of photonic devices further into the near- and midinfrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1?xBix/GaNyAs1?y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 ¼m utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 ¼m is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for longwavelength applications.
The development of laser technology based on silicon continues to be of key importance for the advancement of electronic-photonic integration offering the potential for high data rates and reduced energy consumption. Progress was initially hindered due to the inherent indirect band gap of silicon. However, there has been considerable progress in developing ways of incorporating high gain III-V based direct band gap materials onto silicon, bringing about the advantages of both materials. In this paper, we introduce the need for lasers on silicon and review some of the main approaches for the integration of III-V active regions, including direct epitaxial growth, hybrid integration, defect blocking layers and quantum dots. We then discuss the roles of different carrier recombination processes on the performance of devices formed using both wafer fusion and direct epitaxial approaches.
We show that even in quantum-dot (QD) lasers with very low threshold current densities (J(th) = 40-50 A/cm(2) at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises similar to 60% to 70% of J(th) at 300 K, whereas the radiative part of J(th) is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part Of Jth, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-mu m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.
This paper proposes and demonstrates a new multiquantum well (MQW) laser structure with a temperature-insensitive threshold current and output power. Normally, the mechanisms that cause the threshold current (Ith) of semiconductor lasers to increase with increasing temperature T (thermal broadening of the gain spectrum, thermally activated carrier escape, Auger recombination, and intervalence band absorption) act together to cause Ith to increase as T increases. However, in the design presented here, carriers thermally released from some of the QWs are fed to the other QWs so that these mechanisms compensate rather than augment one another. The idea is in principle applicable to a range of materials systems, structures, and operating wavelengths. We have demonstrated the effect for the first time in 1.5 ¼m GaInAsP/InP Fabry-Perot cavity edge-emitting lasers. The results showed that it is possible to keep the threshold current constant over a temperature range of about 100 K and that the absolute temperature over which the plateau occurred could be adjusted easily by redesigning the quantum wells and the barriers between them. TEM studies of the structures combined with measurements of the electroluminescent intensities from the wells are presented and explain well the observed effects.
InAs quantum-dot (QD) lasers were investigated in the temperature range 20-300 K and under hydrostatic pressure in the range of 0-12 kbar at room temperature. The results indicate that Auger recombination is very important in 1.3-mum QD lasers at room temperature and it is, therefore, the possible cause of the relatively low characteristic temperature observed, of T-0 = 41 K. In the 980-mn QD lasers where T-0 = 110-130 K, radiative recombination dominates. The laser emission photon energy E-las increases linearly with pressure p at 10.1 and 8.3 meV/kbar for 980 nm and 1.3-mum QD lasers, respectively. For the 980-mn QD lasers the threshold current increases with pressure at a rate proportional to the square of the photon energy E-las(2). However, la the threshold current of the 1.3-mum QD laser decreases. by 26% over a 12-kbar pressure range. This demonstrates the presence of a nonradiative recombination contribution to the threshold current, which decreases with increasing pressure. The authors show that this nonradiative contribution is Auger recombination. The results are discussed in the framework of a theoretical model based on the electronic structure and radiative recombination calculations carried out using an 8 x 8 k(.)p Hamiltonian.
Eales Timothy D., Marko Igor P., Schulz Stefan, O?Halloran Edmond, Ghetmiri Seyed, Du Wei, Zhou Yiyin, Yu Shui-Qing, Margetis Joe, Tolle John, O?Reilly Eoin P., Sweeney Stephen J. (2019) Ge1-xSnx alloys: Consequences of band mixing effects for the evolution of the band gap -character with Sn concentration,Scientific Reports
In this work we study the nature of the band gap in GeSn alloys for use in silicon-based lasers. Special attention is paid to Sn-induced band mixing effects. We demonstrate from both experiment and ab-initio theory that the (direct) - character of the GeSn band gap changes continuously with alloy composition and has significant -character even at low (6%) Sn concentrations. The evolution of the -character is due to Sn-induced conduction band mixing effects, in contrast to the sharp indirect-to-direct band gap transition obtained in conventional alloys such as Al1-xGaxAs. Understanding the band mixing effects is critical not only from a fundamental and basic properties viewpoint but also for designing photonic devices with enhanced capabilities utilizing GeSn and related material systems.
Sharpe M. K., Marko I. P., Duffy D. A., England J., Schneider E., Kesaria M., Fedorov V., Clarke E., Tan C. H., Sweeney S. J. (2019) A comparative study of epitaxial InGaAsBi/InP structures using Rutherford backscattering spectrometry, X-ray diffraction and photoluminescence techniques,JOURNAL OF APPLIED PHYSICS 126 (12) 125706
AMER INST PHYSICS
In this work, we used a combination of photoluminescence (PL), high resolution X-ray diffraction (XRD), and Rutherford backscattering
spectrometry (RBS) techniques to investigate material quality and structural properties of MBE-grown InGaAsBi samples (with and without
an InGaAs cap layer) with targeted bismuth composition in the 3%?4% range. XRD data showed that the InGaAsBi layers are more homogeneous in the uncapped samples. For the capped samples, the growth of the InGaAs capped layer at higher temperature affects the quality of the InGaAsBi layer and bismuth distribution in the growth direction. Low-temperature PL exhibited multiple emission peaks; the peak
energies, widths, and relative intensities were used for comparative analysis of the data in line with the XRD and RBS results. RBS data at a
random orientation together with channeled measurements allowed both an estimation of the bismuth composition and analysis of the
structural properties. The RBS channeling showed evidence of higher strain due to possible antisite defects in the capped samples grown at
a higher temperature. It is also suggested that the growth of the capped layer at high temperature causes deterioration of the bismuth-layer
quality. The RBS analysis demonstrated evidence of a reduction of homogeneity of uncapped InGaAsBi layers with increasing bismuth concentration. The uncapped higher bismuth concentration sample showed less defined channeling dips suggesting poorer crystal quality and
clustering of bismuth on the sample surface.
Li Bowei, Xiang Yuren, Imalka Jayawardena K.D.G., Luo Deying, Wang Zhuo, Yang Xiaoyu, Watts John F., Hinder Steven, Sajjad Muhammad T., Webb Thomas, Luo Haitian, Marko Igor, Li Hui, Thomson Stuart A.J., Zhu Rui, Shao Guosheng, Sweeney Stephen J., Silva S. Ravi P., Zhang Wei (2020) Reduced bilateral recombination by functional molecular interface engineering for efficient inverted perovskite solar cells,Nano Energy 105249
Interface-mediated recombination losses between perovskite and charge transport layers are one of the main reasons that limit the device performance, in particular for the open-circuit voltage (VOC) of perovskite solar cells (PSCs). Here, functional molecular interface engineering (FMIE) is employed to retard the interfacial recombination losses. The FMIE is a facile solution-processed means that introducing functional molecules, the fluorene-based conjugated polyelectrolyte (CPE) and organic halide salt (OHS) on both contacts of the perovskite absorber layer. Through the FMIE, the champion PSCs with an inverted planar heterojunction structure show a remarkable high VOC of 1.18 V whilst maintaining a fill factor (FF) of 0.83, both of which result in improved power conversion efficiencies (PCEs) of 21.33% (with stabilized PCEs of 21.01%). In addition to achieving one of the highest PCEs in the inverted PSCs, the results also highlight the synergistic effect of these two molecules in improving device performance. Therefore, the study provides a straightforward avenue to fabricate highly efficient inverted PSCs.