Center for Quantum Devices - Most Downloaded Journal Articles

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15.	Radiative recombination of confined electrons at the MgZnO/ ZnO heterojunction interface Sumin Choi, David J. Rogers, Eric V. Sandana, Philippe Bove, Ferechteh H. Teherani, Christian Nenstiel, Axel Hoffmann, Ryan McClintock, Manijeh Razeghi, David Look, Angus Gentle, Matthew R. Phillips & Cuong Ton-That Nature Scientific Reports 7, pp. 7457-- August 7, 2017 ...[Visit Journal] We investigate the optical signature of the interface in a single MgZnO/ZnO heterojunction, which exhibits two orders of magnitude lower resistivity and 10 times higher electron mobility compared with the MgZnO/Al₂O₃ film grown under the same conditions. These impressive transport properties are attributed to increased mobility of electrons at the MgZnO/ZnO heterojunction interface. Depthresolved cathodoluminescence and photoluminescence studies reveal a 3.2 eV H-band optical emission from the heterointerface, which exhibits excitonic properties and a localization energy of 19.6 meV. The emission is attributed to band-bending due to the polarization discontinuity at the interface, which leads to formation of a triangular quantum well and localized excitons by electrostatic coupling. [reprint (PDF)]
15.	Electrically pumped photonic crystal distributed feedback quantum cascade lasers Y. Bai, S.R. Darvish, S. Slivken, P. Sung, J. Nguyen, A. Evans, W. Zhang, and M. Razeghi Applied Physics Letters, Vol. 91, No. 14, p. 141123-1-- October 1, 2007 ...[Visit Journal] We demonstrate electrically pumped, room temperature, single mode operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting at ~4.75 µm. Ridge waveguides of 100 µm width were fabricated with both PCDFB and Fabry-Pérot feedback mechanisms. The Fabry-Pérot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half maximum of 2.4°. This accomplishment represents the first step in power scaling of single mode, midinfrared laser diodes operating at room temperature. [reprint (PDF)]
15.	High Power, Continuous-Wave, Quantum Cascade Lasers for MWIR and LWIR Applications S. Slivken, A. Evans, J.S. Yu, S.R. Darvish and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 612703-- January 23, 2006 ...[Visit Journal] Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. Since 2002, the power levels for individual devices have jumped from 20 mW to 600 mW. Expanding on this development, we have able to demonstrate continuous wave operation at many wavelengths throughout the mid- and far-infrared spectral range, and have now achieved >100 mW output in the 4.0 to 9.5 µm range. [reprint (PDF)]
15.	Temperature insensitivity of the Al-free InGaAsP/GaAs lasers for λ = 808 and 908 nm M. Razeghi, H. Yi, J. Diaz, S. Kim, and M. Erdtmann SPIE Conference, San Jose, CA; Proceedings 3001-- February 12, 1997 ...[Visit Journal] n this work, we present our recent achievements for the reliability of the Al-free lasers at high temperatures and high powers. Laser operations up to 30,000 hours were achieved without any degradation in the lasers characteristics from 7 randomly selected InGaAsP/GaAs diodes for λ = 808 nm. The test were performed for lasers without mirror-coating for optical power of 0.5 to 1 W CW at 50 approximately 60 °C. To the best of our knowledge, this is the first direct demonstration of the extremely high reliability of Al-free diodes operations at high powers and temperatures for periods of time much longer than practical need (approximately 3 years). The characteristics during the tests are discussed in detail. [reprint (PDF)]
15.	InGaAs/InGaP Quantum-Dot Photodetector with a High Detectivity H. Lim, S. Tsao, M. Taguchi, W. Zhang, A. Quivy and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270N-- January 23, 2006 ...[Visit Journal] Quantum-dot infrared photodetectors (QDIPs) have recently been considered as strong candidates for numerous applications such as night vision, space communication, gas analysis and medical diagnosis involving middle and long wavelength infrared (MWIR and LWIR respectively) operation. This is due to their unique properties arising from their 3-dimensional confinement potential that provides a discrete density of states. They are expected to outperform quantum-well infrared photodetectors (QWIPs) as a consequence of their natural sensitivity to normal incident radiation, their higher responsivity and their higher-temperature operation. So far, most of the QDIPs reported in the literature were based on the InAs/GaAs system and were grown by molecular beam epitaxy (MBE). Here, we report on the growth of a high detectivity InGaAs/InGaP QDIP grown on a GaAs substrate using low-pressure metalorganic chemical vapor deposition (MOCVD). [reprint (PDF)]
15.	Disorder of a Gax In1-xAsy P1-y-InP quantum well by Zn diffusion M. Razeghi, O. Acher, and F. Launay Semicond. Sci. Technol. 2 (1 987) 793-796.-- July 30, 1987 ...[Visit Journal] Data are presented showing for the first time that Zn diffusion into a Ga,In,-,As,P,-, - InP quantum well and superlattice (of 100 A thickness) completely disorders the quantum well and superlattice layers. The photoluminescence wavelength of the quantum well and the superlattice increased after Zn diffusion, which can be attributed to the In-Ga interdiffusion at the heterointerfaces, as a result of the interchange mechanism between the interstitials and substitutional zinc atoms [reprint (PDF)]
15.	High differential resistance type-II InAs/GaSb superlattice photodiodes for the long-wavelength infrared A. Hood, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E. Michel and M. Razeghi Applied Physics Letters, 89 (9)-- August 28, 2006 ...[Visit Journal] Type-II InAs/GaSb superlattice photodiodes with a 50% cutoff wavelength ranging from 11 to 13 μm are presented. Optimization of diffusion limited photodiodes provided superlattice structures for improved injection efficiency in direct injection hybrid focal plane array applications. [reprint (PDF)]
15.	Review of III-Nitride Optoelectronic Materials for light Emission and Detection M. Razeghi, A. Yasan, R. McClintock, K. Mayes, D. Shiell, S. Darvish, and P. Kung Physica Status Solidi C S141 - S148-- September 10, 2004 ...[Visit Journal] We review the significant achievements relating to optoelectronic devices based on III-nitrides at the center for quantum devices (CQD). Based on GaN/InGaN multiple-quantum well structures, we demonstrated blue laser diodes at a wavelength of 405 nm. This achievement was particularly significant at the time, because while no defect reduction technique was used, a fairly low threshold current density was achieved (3.8 kA/cm²). In the past few years, however, the interest has shifted towards shorter wavelength light emitters, i.e. ultraviolet LEDs and LDs. Lower crystalline quality and unsatisfactory doping levels of AlGaN compound semiconductors posed serious challenges en route to the realization of UV light emitters. However, steady progress in the growth of AlGaN and AlN epilayers made it possible to overcome some of the difficulties. To date, we have been able to demonstrate UV LEDs at wavelengths as short as 265 nm (corresponding to 45% Al in Al_xGa_1-xN) with optical output powers of over 5 mW. We have addressed the n-type AlGaN doping problem by using a Si-In co-doped scheme. We also employed high-quality AlGaN/AlN superlattice templates for the reduction of defects. We have also demonstrated 280 nm UV LEDs with output powers of over 6 mW and external quantum efficiencies of over 0.25%. Despite all the success in the realization of short-wavelength UV LEDs, UV laser diodes at these short wavelengths are yet to be realized. The main difficulties are the low material quality, high device resistance leading to excessive heating of the device, realization of smooth cavity mirrors, and issues related to the cracking of the material. We have also demonstrated different types of photodetectors in the UV range of the spectrum: photoconductors, MSM photodetector, Schottky barrier photodetectors, and p-i-n photodiodes to name a few. The most promising type of photodetector for realization of UV imaging focal plane arrays is the p-i-n photodiode. Realization of high-efficiency AlGaN-based p-i-n photodiodes becomes more difficult when considering the need for the collection of the light from the backside of the substrate. However, similar to our back-emission UV LED structure, we have demonstrated back-illuminated p-i-n solar-blind photodiodes with external quantum efficiencies as high as 68% under no applied bias and 74% under -5 V of bias. [reprint (PDF)]
15.	Band-gap narrowing and potential fluctuation in Si-doped GaN I.H. Lee, J.J. Lee, P. Kung, F.J. Sanchez, and M. Razeghi Applied Physics Letters 74 (1)-- January 4, 1999 ...[Visit Journal] We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities. [reprint (PDF)]
15.	Growth of Al_xGa_1-xN:Ge on sapphire and silicon substrates X. Zhang, P. Kung, A. Saxler, D. Walker, T.C. Wang, and M. Razeghi Applied Physics Letters 67 (12)-- September 18, 1995 ...[Visit Journal] Al_xGa_1–xN were grown on (00.1) sapphire and (111) silicon substrates in the whole composition range (0 <= x <= 1). The high optical quality of the epilayers was assessed by room-temperature optical absorption and photoluminescence measurements. Layers with higher Al composition are more resistive. Resistive Al_xGa_1–xN epilayers were successfully doped with Ge and free-electron concentration as high as 3 × 10¹⁹ cm^–3 was achieved. [reprint (PDF)]
15.	Persistent photoconductivity in thin undoped GaInP/GaAs quantum wells S. Elhamri, M. Ahoujja, K. Ravindran, D.B. Mast, R.S. Newrock, W.C. Mitchel, G.J. Brown, I. Lo, M. Razeghi and X. He Applied Physics Letters 66 (2)-- January 9, 1995 ...[Visit Journal] Persistent photoconductivity has been observed at low temperatures in thin, unintentionally doped GaInP/GaAs/GaInP quantum wells. The two‐dimensional electron gas was studied by low field Hall and Shubnikov–de Haas effects. After illumination with red light, the electron concentration increased from low 10¹¹ cm⁻² to more than 7×10¹¹ cm⁻² resulting in an enhancement of both the carrier mobility and the quantum lifetime. The persistent photocarriers cannot be produced by DX-like defects since the shallow dopant concentration in the GaInP layers is too low to produce the observed concentration. We suggest that the persistent carriers are produced by photoionization of deep intrinsic donors in the GaInP barrier layer. We also report observation of a parallel conduction path in GaInP induced by extended illumination. [reprint (PDF)]
15.	Overview of Quantum Cascade Laser Research at the Center for Quantum Devices S. Slivken, A. Evans, J. Nguyen, Y. Bai, P. Sung, S.R. Darvish, W. Zhang and M. Razeghi SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 69000B-1-8.-- February 1, 2008 ...[Visit Journal] Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. In the past year alone, the efficiency and power of our short wavelength lasers (~4.8 µm) has doubled. In continuous wave at room temperature, we have now separately demonstrated ~10% wallplug efficiency and ~700 mW of output power. Up to now, we have been able to show that room temperature continuous wave operation with > 100 mW output power in the 3.8 < λ < 11.5 µm wavelength range is possible. [reprint (PDF)]
15.	Effects of substrate quality and orientation on the characteristics of III-nitride resonant tunneling diodes Z. Vashaei, C. Bayram, R. McClintock and M. Razeghi SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol 7945, p. 79451A-- January 23, 2011 ...[Visit Journal] Al(Ga)N/GaN resonant tunneling diodes (RTDs) are grown by metal-organic chemical vapor deposition. The effects of material quality on room temperature negative differential resistance (NDR) behaviour of RTDs are investigated by growing the RTD structure on AlN, GaN, and lateral epitaxial overgrowth GaN templates. This reveals that NDR characteristics of RTDs are very sensitive to material quality (such as surface roughness and dislocations density). The effects of the aluminum content of AlGaN double barriers (DB) and polarization fields on NDR characteristic of AlGaN/GaN RTDs were also investigated by employing low dislocation density c-plane (polar) and m-plane (nonpolar) freestanding GaN substrates. Lower aluminum content in the DB RTD active layer and minimization of dislocations and polarization fields enabled a more reliable and reproducible NDR behaviour at room temperature. [reprint (PDF)]
15.	Ga/sub 0.51/In/sub 0.49/P/GaAs HEMT's exhibiting good electrical performance at cryogenic temperatures Y.-J. Chan; D. Pavlidis; M. Razeghi; F. Omnes IEEE TRANS. ELEC.DEVICES. 77. IO. 1990-- October 1, 1990 ...[Visit Journal] The DC and microwave characteristics of Ga/sub 0.51/In/sub 0.49/P/GaAs HEMTs grown by metalorganic chemical vapor deposition (MOCVD) are presented. Devices with 1- mu m-long gates show transconductances of 163 and 213 mS/mm at 300 and 77 K, respectively. Their maximum cutoff frequency is 17.8 GHz. Deep traps in the doped layer are evaluated at low temperature by the threshold voltage shift and current collapse phenomena. GaInP/GaAs HEMTs show no current collapse and have almost zero threshold voltage shift compared to AlGaAs/GaAs and InAlAs/InGaAs where the corresponding values are 0.5 and 0.25 V, respectively. [reprint (PDF)]
15.	Recent advances in high performance antimonide-based superlattice FPAs E.K. Huang, B.M. Nguyen, S.R. Darvish, S. Abdollahi Pour, G. Chen, A. Haddadi, and M.A. Hoang SPIE Proceedings, Infrared technology and Applications XXXVII, Orlando, FL, Vol. 8012, p. 80120T-1-- April 25, 2011 ...[Visit Journal] Infrared detection technologies entering the third generation demand performances for higher detectivity, higher operating temperature, higher resolution and multi-color detection, all accomplished with better yield and lower manufacturing/operating costs. Type-II antimonide based superlattices (T2SL) are making firm steps toward the new era of focal plane array imaging as witnessed in the unique advantages and significant progress achieved in recent years. In this talk, we will present the four research themes towards third generation imagers based on T2SL at the Center for Quantum Devices. High performance LWIR megapixel focal plane arrays (FPAs) are demonstrated at 80K with an NEDT of 23.6 mK using f/2 optics, an integration time of 0.13 ms and a 300 K background. MWIR and LWIR FPAs on non-native GaAs substrates are demonstrated as a proof of concept for the cost reduction and mass production of this technology. In the MWIR regime, progress has been made to elevate the operating temperature of the device, in order to avoid the burden of liquid nitrogen cooling. We have demonstrated a quantum efficiency above 50%, and a specific detectivity of 1.05x10¹² cm·Hz^1/2/W at 150 K for 4.2 μm cut-off single element devices. Progress on LWIR/LWIR dual color FPAs as well as novel approaches for FPA fabrication will also be discussed. [reprint (PDF)]
15.	Crystallography of epitaxial growth of wurtzite-type thin films on sapphire substrates P. Kung, C.J. Sun, A. Saxler, H. Ohsato, and M. Razeghi Journal of Applied Physics 75 (9)-- May 1, 1994 ...[Visit Journal] In this article, we present a crystallographic model to describe the epitaxial growth of wurtzite‐type thin films such as gallium nitride (GaN) on different orientations of sapphire (Al2O3) substrates. Through this model, we demonstrate the thin films grown on (00⋅1)Al₂O₃ have a better epilayer‐substrate interface quality than those grown on (01⋅2)Al₂O₃. We also show the epilayer grown on (00⋅1)Al₂O₃ are gallium‐terminated, and both (00⋅1) and (01⋅2) surfaces of sapphire crystals are oxygen‐terminated. [reprint (PDF)]
15.	8-13 μm InAsSb heterojunction photodiode operating at near room temperature J.D. Kim, S. Kim, D. Wu, J. Wojkowski, J. Xu, J. Piotrowski, E. Bigan, and M. Razeghi Applied Physics Letters 67 (18)-- October 30, 1995 ...[Visit Journal] p⁺-InSb/π-InAs_1−xSb_x/n⁺-InSb heterojunction photodiodes operating at near room temperature in the 8–13 μm region of infrared (IR) spectrum are reported. A room‐temperature photovoltaic response of up to 13 μm has been observed at 300 K with an x≊0.85 sample. The voltage responsivity‐area product of 3×10⁻⁵ V· cm²/W has been obtained at 300 K for the λ=10.6 μm optimized device. This was close to the theoretical limit set by the Auger mechanism, with a detectivity at room temperature of ≊1.5×10⁸ cm ·Hz^½/W. [reprint (PDF)]
15.	High Carrier Lifetime InSb Grown on GaAs Substrates E. Michel, H. Mohseni, J.D. Kim, J. Wojkowski, J. Sandven, J. Xu, M. Razeghi, R. Bredthauer, P. Vu, W. Mitchel, and M. Ahoujja Applied Physics Letters 71 (8-- August 25, 1997 ...[Visit Journal] We report on the growth of near bulklike InSb on GaAs substrates by molecular beam epitaxy despite the 14% lattice mismatch between the epilayer and the substrate. Structural, electrical, and optical properties were measured to assess material quality. X-ray full widths at half-maximum were as low as 55 arcsec for a 10 µm epilayer, peak mobilities as high as ~ 125 000 cm2/V s, and carrier lifetimes up to 240 ns at 80 K. [reprint (PDF)]
15.	Optical losses of Al-free lasers for λ = 0.808 and 0.98 μm H. Yi, J. Diaz, B. Lane, and M. Razeghi Applied Physics Letters 69 (20)-- November 11, 1996 ...[Visit Journal] In this work, we study the origin of the optical losses in Al‐free InGaAsP/GaAs (λ=0.808 μm) and InGaAs/GaAs/InGaP (λ=0.980 μm) lasers. Theoretical modeling and the experimental results indicate that the scattering of the laser beam by refractive index fluctuation in the alloys is the dominant loss in our lasers, and the loss due to the free‐carrier absorption and scattering by interface roughness are negligible. [reprint (PDF)]
15.	Band edge tunability of M-structure for heterojunction design in Sb based Type-II superlattice photodiodes B.M. Nguyen, D. Hoffman, P.Y. Delaunay, E.K. Huang, M. Razeghi, and J. Pellegrino Applied Physics Letters, Vol. 93, No. 16, p. 163502-1-- October 20, 2008 ...[Visit Journal] We present theoretically and experimentally the effect of the band discontinuity in Type-II misaligned InAs/GaSb superlattice heterodiodes. Calculations using the empirical tight binding method have shown the great flexibility in tuning the energy levels of the band edge in M-structure superlattice as compared to the standard InAs/GaSb superlattice. Through the experimental realization of several p-pi-M-n photodiodes, the band discontinuity alignment between the standard binary-binary superlattice and the M-structured superlattice was investigated via optical characterization. The agreement between the theoretical predictions and the experimental measurement confirms the capability of controlling the M-structure band edges and suggests a way to exploit this advantage for the realization of heterostructures containing an M-structured superlattice without bias dependent operation. [reprint (PDF)]
15.	Comparison of PLD-Grown p-NiO/n-Ga2O3 Heterojunctions on Bulk Single Crystal β-Ga2O3 and r-plane Sapphire Substrates D. J. Rogers , V. E. Sandana, F. Hosseini Teherani and M. Razeghi Proc. of SPIE Vol. 12895, Quantum Sensing and Nano Electronics and Photonics XX, 128870J (28 January - 1 February 2024 San Francisco)doi: 10.1117/12.3012511 ...[Visit Journal] p-NiO/n-Ga2O3 heterostructures were formed on single crystal (-201) β (monoclinic) Ga2O3 and r-sapphire substrates by Pulsed Laser Deposition. Ring mesa layer stacks were created using a shadow mask during growth. X-Ray diffraction studies were consistent with the formation of (111) oriented fcc NiO on the bulk Ga2O3 and randomly oriented fcc NiO on (102) oriented β-Ga2O3 /r-sapphire. RT optical transmission studies revealed bandgap energy values of ~3.65 eV and ~5.28 eV for the NiO and Ga2O3 on r-sapphire. p-n junction devices were formed by depositing gold contacts on the layer stacks using shadow masks in a thermal evaporator. Both heterojunctions showed rectifying I/V characteristics. On bulk Ga2O, the junction showed a current density over 16mA/cm2 at +20V forward bias and a reverse bias leakage current over 3 orders of magnitude lower at -20V (1 pA). On Ga2O3/r-sapphire the forward bias current density at +15V was about an order of magnitude lower than for the p-NiO/bulk n-Ga2O3 heterojunction while the reverse bias leakage current at -15V (~ 20 pA) was an order of magnitude higher. Hence the NiO/bulk Ga2O3 junction was more rectifying. Upon illumination with a Xenon lamp a distinct increase in current was observed for the IV curves in both devices (four orders of magnitude for -15V reverse bias in the case of the p-NiO/bulk n-Ga2O3 heterojunction). The p-NiO/n-Ga2O3/rsapphire junction gave a spectral responsivity with a FWHM value of 80nm and two distinct response peaks (with maxima at 230 and 270nm) which were attributed to carriers being photogenerated in the Ga2O3 underlayer. For both devices time response studies showed a 10%/90% rise and fall of the photo generated current upon shutter open and closing which was relatively abrupt (millisecond range), and there was no evidence of significant persistent photoconductivity. [reprint (PDF)]
15.	Engineering Multi-Section Quantum Cascade Lasers for Broadband Tuning Steven Slivken and Manijeh Razeghi Photonics 3, 41-- June 27, 2016 ...[Visit Journal] In an effort to overcome current limitations to electrical tuning of quantum cascade lasers, a strategy is proposed which combines heterogeneous quantum cascade laser gain engineering with sampled grating architectures. This approach seeks to not only widen the accessible spectral range for an individual emitter, but also compensate for functional non-uniformity of reflectivity and gain lineshapes. A trial laser with a dual wavelength core is presented which exhibits electroluminescence over a 750 cm⁻¹ range and discrete single mode laser emission over a 700 cm⁻¹ range. Electrical tuning over 180 cm⁻¹ is demonstrated with a simple sampled grating design. A path forward to even wider tuning is also described using more sophisticated gain and grating design principles. [reprint (PDF)]
15.	Reliability in room-temperature negative differential resistance characteristics of low-aluminum contact AlGaN/GaN double-barrier resonant tunneling diodes C. Bayram, Z. Vashaei, and M. Razeghi Applied Physics Letters, Vol. 97, No. 18, p. 181109-1-- November 1, 2010 ...[Visit Journal] AlGaN/GaN resonant tunneling diodes (RTDs), consisting of 20% (10%) aluminum-content in double-barrier (DB) active layer, were grown by metal-organic chemical vapor deposition on freestanding polar (c-plane) and nonpolar (m-plane) GaN substrates. RTDs were fabricated into 35-μm-diameter devices for electrical characterization. Lower aluminum content in the DB active layer and minimization of dislocations and polarization fields increased the reliability and reproducibility of room-temperature negative differential resistance (NDR). Polar RTDs showed decaying NDR behavior, whereas nonpolar ones did not significantly. Averaging over 50 measurements, nonpolar RTDs demonstrated a NDR of 67 Ω, a current-peak-to-valley ratio of 1.08, and an average oscillator output power of 0.52 mW. [reprint (PDF)]
15.	Type II superlattice infrared detectors and focal plane arrays Vaidya Nathan; Manijeh Razeghi Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 654209 (May 14, 2007)-- May 14, 2007 ...[Visit Journal] Type II superlattce photodetectors have recently experienced significant improvements in both theoretical structure design and experimental realization. Empirical Tight Binding Method is initiated and developed for Type II superlattice. Growth characteristics such as group V segregation and incorporation phenomena are taken into account in the model and shown higher precision. A new Type II structure, called M-structure, is introduced and theoretically demonstrated high R₀A, high quantum efficiency. Device design is optimized to improve the performance. As a result, 55% quantum efficiency and 10 Ohm·cm² R₀A are achieved for an 11.7 μm cut-off photodetector at 77K. FPA imaging at longwavelength is demonstrated with a capability of imaging up to 171K. At 81K, the noise equivalent temperature difference presented a peak at 0.33K. [reprint (PDF)]
15.	Injector doping level dependent continuous-wave operation of InP-based QCLs at λ~ 7.3 µm above room temperature J.S. Yu, S. Slivken, and M. Razeghi Semiconductor Science and Technology (SST), Vol. 25, No. 12, p. 125015-- December 1, 2010 ...[Visit Journal] We report the continuous-wave (CW) operation of InGaAs/InAlAs quantum cascade lasers (QCLs) operating at λ ~ 7.3 µm above room temperature. The injector doping level–dependent CW characteristics above room temperature are investigated for doping densities between 7 × 10¹⁶ cm⁻³ and 2 × 10¹⁷ cm⁻³. The device performance, i.e. threshold current density, output power, operating temperature and characteristic temperature, depends strongly on the injector doping density. For a relatively low injector doping density of 7 × 10¹⁶ cm⁻³, a high-reflectivity-coated 10 µm wide and 4 mm long laser exhibits an improved device performance with an output power of 152 mW and a threshold current density of 1.37 kA cm⁻² at 298 K under CW mode, operating up to 343 K. The thermal characteristics are also analyzed by the estimation from the experimentally measured data for the QCLs with different injector doping densities. [reprint (PDF)]

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