Center for Quantum Devices - Most Downloaded Journal Articles

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14.	Tight-binding theory for the thermal evolution of optical band gaps in semiconductors and superlattices S. Abdollahi Pour, B. Movaghar, and M. Razeghi American Physical Review, Vol. 83, No. 11, p. 115331-1-- March 15, 2011 ...[Visit Journal] A method to handle the variation of the band gap with temperature in direct band-gap III–V semiconductors and superlattices using an empirical tight-binding method has been developed. The approach follows closely established procedures and allows parameter variations which give rise to perfect fits to the experimental data. We also apply the tight-binding method to the far more complex problem of band structures in Type-II infrared superlattices for which we have access to original experimental data recently acquired by our group. Given the close packing of bands in small band-gap Type-II designs, k·p methods become difficult to handle, and it turns out that the sp3s* tight-binding scheme is a practical and powerful asset. Other approaches to band-gap shrinkage explored in the past are discussed, scrutinized, and compared. This includes the lattice expansion term, the phonon softening mechanism, and the electron-phonon polaronic shifts calculated in perturbation theory. [reprint (PDF)]
14.	Comprehensive study of blue and green multi-quantum-well light-emitting diodes grown on conventional and lateral epitaxial overgrowth GaN C. Bayram, J.L. Pau, R. McClintock and M. Razeghi Applied Physics B: Lasers and Optics, Vol. 95, p. 307-314-- November 29, 2008 ...[Visit Journal] Growths of blue and green multi-quantum wells (MQWs) and light-emitting diodes (LEDs) are realized on lateral epitaxial overgrowth (LEO) GaN, and compared with identical structures grown on conventional GaN. Atomic force microscopy is used to confirm the significant reduction of dislocations in the wing region of our LEO samples before active-region growth. Differences between surface morphologies of blue and green MQWs are analyzed. These MQWs are integrated into LEDs. All devices show a blue shift in the electroluminescence (EL) peak and narrowing in EL spectra with increasing injection current, both characteristics attributed to the band-gap renormalization. Green LEDs show a larger EL peak shift and a broader EL spectrum due to larger piezoelectric field and more indium segregation in the MQWs, respectively. Blue LEDs on LEO GaN show a higher performance than those on conventional GaN; however, no performance difference is observed for green LEDs on LEO GaN versus conventional GaN. The performance of the green LEDs is shown to be primarily limited by the active layer growth quality. [reprint (PDF)]
14.	Room temperature single-mode terahertz sources based on intracavity difference-frequency generation in quantum cascade lasers Q.Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi Applied Physics Letters, Vol. 99, Issue 13, p. 131106-1-- September 26, 2011 ...[Visit Journal] We demonstrate room temperature single-mode THz emission at 4 THz based on intracavity difference-frequency generation from mid-infrared dual-wavelength quantum cascade lasers. An integrated dual-period distributed feedback grating is defined on the cap layer to purify both mid-infrared pumping wavelengths and in turn the THz spectra. Single mode operation of the pumping wavelengths results in a single-mode THz operation with a narrow linewidth of 6.6 GHz. A maximum THz power of 8.5 μW with a power conversion efficiency of 10 μW/W² is obtained at room temperature. [reprint (PDF)]
14.	Improved performance of IR photodetectors with 3D gap engineering J. Piotrowski and M. Razeghi Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal] The ultimate signal-to-noise performance of the semiconductor photodetector is limited by the statistical fluctuations of the thermal generation and recombination rates in photodetector material. Cooling is an effective but impractical way of suppression of the thermal processes. The performance of uncooled detectors can be improved by minimizing the thermal generation and recombination rates and reducing the actual volume of photodetector. This can be realized in 3D heterostructure devices. In these devices, the incident radiation is absorbed in small regions of narrow gap semiconductor, buried in wide gap volume and supplied with wide gap electric contacts and radiation concentrators. The practical near room-temperature 1 - 12 μm IR heterostructure photodetectors are reported. The devices are based on variable gap Hg_1-xCd_xTe. The 3D heterostructures have been obtained by Isothermal Vapor Growth Epitaxy in a reusable growth system which enables in situ doping during growth with foreign impurities. Ion milling was extensively used in preparation of the devices. Monolithic optical immersion has been applied for further improvement of performance. The 3D heterostructure devices exhibit performance exceeding that of conventional photodetectors. [reprint (PDF)]
14.	Internal Stress Around Micropipes in 6H-SiC Substrates H. Ohsato, T. Kato, T. Okuda and M. Razeghi SPIE Conference, San Jose, CA, -- January 27, 1999 ...[Visit Journal] 6H-SiC single crystals are expected to be suitable substrates for thin film growth of the wide bandgap semiconductor (GaN, because it has a small lattice mismatch with GaN. Moreover, SiC single crystals are also expected for high-power and high- temperature electric applications because of its wide band gap, high breakdown voltage, high thermal conductivity and high temperature stability. Single crystals with large size used for electronic devices can be grown on seed crystals only by the modified Lely method based on sublimation deposition. But, single crystals have serious defects so called micropipes. These micropipes penetrate almost along the [001] direction. The internal strain around micropipes was investigated using the polarizing optical microscope for the purpose of clarifying the formation mechanisms and decreasing the amount of micropipes. A special interference figure was found around a micropipe under the crossed polars on the polarizing microscope. In this work, the special interference figure around micropipes due to internal stress was explained, and the magnitude and distribution of the stress was measured by means of photoelasticity and the mapping of Raman spectra. [reprint (PDF)]
14.	Demonstration of high performance long wavelength infrared Type-II InAs/GaSb superlattice photodidoe grown on GaAs substrate S. Abdollahi Pour, B.M. Nguyen, S. Bogdanov, E.K. Huang, and M. Razeghi Applied Physics Letters, Vol. 95, No. 17, p. 173505-- October 26, 2009 ...[Visit Journal] We report the growth and characterization of long wavelength infrared type-II InAs/GaSb superlattice photodiodes with a 50% cut-off wavelength at 11 µm, on GaAs substrate. Despite a 7.3% lattice mismatch to the substrate, photodiodes passivated with polyimide exhibit an R₀A value of 35 Ω·cm² at 77 K, which is in the same order of magnitude as reference devices grown on native GaSb substrate. With a reverse applied bias less than 500 mV, the dark current density and differential resistance-area product are close to that of devices on GaSb substrate, within the tolerance of the processing and measurement. The quantum efficiency attains the expected value of 20% at zero bias, resulting in a Johnson limited detectivity of 1.1×10¹¹ Jones. Although some difference in performances is observed, devices grown on GaAs substrate already attained the background limit performance at 77 K with a 300 K background and a 2-π field of view. [reprint (PDF)]
14.	High quantum efficiency two color type-II InAs/GaSb n-i-p-p-i-n photodiodes P.Y. Delaunay, B.M. Nguyen, D. Hoffman, A. Hood, E.K. Huang, M. Razeghi, and M.Z. Tidrow Applied Physics Letters, Vol. 92, No. 11, p. 111112-1-- March 17, 2008 ...[Visit Journal] A n-i-p-p-i-n photodiode based on type-II InAs/GaSb superlattice was grown on a GaSb substrate. The two channels, with respective 50% of responsivity cutoff wavelengths at 7.7 and 10 µm, presented quantum efficiencies (QEs) of 47% and 39% at 77 K. The devices can be operated as two diodes for simultaneous detection or as a single n-i-p-p-i-n detector for sequential detection. In the latter configuration, the QEs at 5.3 and 8.5 µm were measured as high as 40% and 39% at 77 K. The optical cross-talk between the two channels could be reduced from 0.36 to 0.08 by applying a 50 mV bias. [reprint (PDF)]
14.	Demonstration of high performance bias-selectable dual-band short-/mid-wavelength infrared photodetectors based on type-II InAs/GaSb/AlSb superlattices A.M. Hoang, G. Chen, A. Haddadi and M. Razeghi Applied Physics Letters, Vol. 102, No. 1, p. 011108-1-- January 7, 2013 ...[Visit Journal] High performance bias-selectable dual-band short-/mid-wavelength infrared photodetector based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm and 4 μm was demonstrated. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0 × 10⁻⁹ A/cm² at −50 mV bias voltage, providing an associated shot noise detectivity of 3.0 × 10¹³ Jones. The mid-wavelength channel exhibited a quantum efficiency of 33% and a dark current density of 2.6 × 10⁻⁵ A/cm² at 300 mV bias voltage, resulting in a detectivity of 4.0 × 10¹¹ Jones. The spectral cross-talk between the two channels was also discussed for further optimization. [reprint (PDF)]
14.	Monolithic integration of a short‐length GaInAs photoconductor with a GaAs/GaAlAs optical waveguide on a GaAs semi‐insulating substrate F. Mallecot; J. F. Vinchant; M. Razeghi; D. Vandermoere; J. P. Vilcot; D. Decoster Appl. Phys. Lett. 53, 2522–2524 (1988)-- December 19, 1988 ...[Visit Journal] We report the first fabrication of a GaO. 47 Inn. 53 As planar photoconductive detector, associated with a GaAs/GaAIAs rib waveguide grown on a semi-insulating GaAs substrate, which needs a short-length absorbing layer to detect the optical signal. Because of the GaAIAs epilayer, a GalnAs length of about 100 tl1n only is needed to detect 90% of the opticai signal, accordingly to results predicted using a four-layer model with complex refractive indices in each layer. [reprint (PDF)]
14.	Quantum Hall liquid-to-insulator transition in In_1-xGa_xAs/InP heterostructures W. Pan, D. Shahar, D.C. Tsui, H.P. Wei, and M. Razeghi Physical Review B 55 (23)-- June 15, 1997 ...[Visit Journal] We report a temperature- and current-scaling study of the quantum Hall liquid-to-insulator transition in an In_1-xGa_xAs/InP heterostructure. When the magnetic field is at the critical field B_c, ρ_xx=0.86h/e². Furthermore, the transport near B_c scales as \|B- Bc\|T^-κ with κ=0.45±0.05, and as \|B- Bc\|I^-b with b=0.23±0.05. The latter can be due to phonon emission in a dirty piezoelectric medium, or can be the consequence of critical behavior near B_c, within which z=1.0±0.1 and ν=2.1±0.3 are obtained from our data. [reprint (PDF)]
14.	Two‐dimensional electron gas in a In0.53Ga0.47As‐InP heterojunction grown by metalorganic chemical vapor deposition Y. Guldner; J. P. Vieren; P. Voisin; M. Voos; M. Razeghi; M. A. Poisson Y. Guldner, J. P. Vieren, P. Voisin, M. Voos, M. Razeghi, M. A. Poisson; Two‐dimensional electron gas in a In0.53Ga0.47As‐InP heterojunction grown by metalorganic chemical vapor deposition. Appl. Phys. Lett. 15 May 1982; 40 (10): 877–879.-- April 15, 1982 ...[Visit Journal] We report, from Shubnikov-de Haas and cyclotron resonance experiments, the first observation of a two-dimensional, high-mobility electron gas in a selectively doped 1110.53 G~l.47 As-InP heterojunction grown by metalorganic chemical vapor deposition. Several parameters of the electronic system under consideration are determined. [reprint (PDF)]
14.	Theoretical investigation of minority carrier leakage of high-power 0.8 μm InGaAsP/InGaP/GaAs laser diodes J. Diaz, I. Eliashevich, H.J. Yi, M. Stanton, and M. Razeghi Applied Physics Letters 65 (18)-- October 31, 1994 ...[Visit Journal] We report a theoretical model that accurately describes the effects of minority carrier leakage from the InGaAsP waveguide into InGaP cladding layers in high‐power aluminum-free 0.8 μm InGaAsP/InGaP/GaAs separate confinement heterostructure lasers. Current leakage due to the relatively low band‐gap discontinuity between the active region and the InGaP barrier can be eliminated by employing laser diodes with cavity length longer than 500 μm. Experimental results for lasers grown by low-pressure metalorganic chemical vapor deposition are in excellent agreement with the theoretical model. [reprint (PDF)]
14.	Uncooled operation of Type-II InAs/GaSb superlattice photodiodes in the mid- wavelength infrared range Y. Wei, A. Hood, H. Yau, A. Gin, M. Razeghi, M.Z. Tidrow, V. Natha Applied Physics Letters, 86 (23)-- June 6, 2005 ...[Visit Journal] We report high performance uncooled midwavelength infrared photodiodes based on interface-engineered InAs/GaSb superlattice. Two distinct superlattices were designed with a cutoff wavelength around 5 µm for room temperature and 77 K. The device quantum efficiency reached more than 25% with responsivity around 1 A/W. Detectivity was measured around 10⁹ cm·Hz^½/W at room temperature and 1.5×10¹³ cm·Hz^½/W at 77 K under zero bias. The devices were without antireflective coating. The device quantum efficiency stays at nearly the same level within this temperature range. Additionally, Wannier–Stark oscillations in the Zener tunneling current were observed up to room temperature. [reprint (PDF)]
14.	Thermal analysis of buried heterostructure quantum cascade lasers for long-wavelength infrared emission using 2D anisotropic heat-dissipation model H.K. Lee, K.S. Chung, J.S. Yu and M. Razeghi Physica Status Solidi (a), Vol. 206, p. 356-362-- February 1, 2009 ...[Visit Journal] We have theoretically investigated and compared the thermal characteristics of 10.6 μm InGaAs/InAlAs/InP buried heterostructure (BH) quantum cascade lasers (QCLs) with different heat-sinking configurations by a steady-state heat-transfer analysis. The heat-source densities were obtained from laser threshold power densities measured experimentally under room-temperature continuous-wave mode. The two-dimensional anisotropic heat-dissipation model was used to calculate the temperature distribution, heat flux, and thermal conductance (Gth) inside the device. For good thermal characteristics, the QCLs in the long-wavelength infrared region require the relatively narrow BH structure in combination with epilayer-down bonding due to thick active core/cladding layers and high insulator losses. The single-ridge BH structure results in slightly higher thermal conductance by 2-4% than the double-channel (DC) ridge BH structure. For W = 12 m with 5 μm thick electroplated Au, the single-ridge BH laser with epilayer-down bonding exhibited the highest G_th value of 201.9 W/K cm², i.e. increased by nearly 36% with respect to the epilayer-up bonded DC ridge waveguide laser. This value is improved by 50% and 62% with respect to the single-ridge BH laser and DC ridge waveguide laser with W = 20 μm in the epilayer-up bonding scheme, respectively. [reprint (PDF)]
14.	Comparison of the Physical Properties of GaN Thin Films Deposited on (0112) and (0001) Sapphire Substrates C.J. Sun and M. Razeghi Applied Physics Letters 63 (7)-- August 16, 1993 ...[Visit Journal] A direct comparison of the physical properties of GaN thin films is made as a function of the choice of substrate orientations. Gallium nitride single crystals were grown on (0001) and (0112) sapphire substrates by metalorganic chemical vapor deposition. Better crystallinity with fine ridgelike facets is obtained on the (0112) sapphire. Also lower carrier concentration and higher mobilities indicate both lower nitrogen vacancies and less oxygen incorporation on the (0112) sapphire. The results of this study show better physical properties of GaN thin films achieved on (0112) sapphire. [reprint (PDF)]
14.	Type-II Antimonide-based Superlattices for the Third Generation Infrared Focal Plane Arrays Manijeh Razeghi, Edward Kwei-wei Huang, Binh-Minh Nguyen, Siamak Abdollahi Pour, and Pierre-Yves Delaunay SPIE Proceedings, Infrared Technology and Applications XXXVI, Vol. 7660, pp. 76601F-- May 10, 2010 ...[Visit Journal] In recent years, the Type-II superlattice (T2SL) material platform has seen incredible growth in the understanding of its material properties which has lead to unprecedented development in the arena of device design. Its versatility in band-structure engineering is perhaps one of the greatest hallmarks of the T2SL that other material platforms are lacking. In this paper, we discuss advantages of the T2SL, specifically the M-structure T2SL, which incorporates AlSb in the traditional InAs/GaSb superlattice. Using the M-structure, we present a new unipolar minority electron detector coined as the p-M-p, the letters which describe the composition of the device. Demonstration of this device structure with a 14 μm cutoff attained a detectivity of 4x10¹⁰ Jones (-50 mV) at 77 K. As device performance improves year after year with novel design contributions from the many researchers in this field, the natural progression in further enabling the ubiquitous use of this technology is to reduce cost and support the fabrication of large infrared imagers. In this paper, we also discuss the use of GaAs substrates as an enabling technology for third generation imaging on T2SLs. Despite the 7.8% lattice mismatch between the native GaSb and alternative GaAs substrates, T2SL photodiodes grown on GaAs at the MWIR and LWIR have been demonstrated at an operating temperature of 77 K [reprint (PDF)]
14.	320x256 infrared focal plane array based on type-II InAs/GaSb superlattice with a 12 μm cutoff wavelength P.Y. Delaunay, B.M. Nguyen, D. Hoffman, and M. Razeghi SPIE Porceedings, Vol. 6542, Orlando, FL 2007, p. 654204-- April 9, 2007 ...[Visit Journal] In the past few years, significant progress has been made in the structure design, growth and processing of Type-II InAs/GaSb superlattice photodetectors. Type-II superlattice demonstrated its ability to perform imaging in the middle and long infra-red range, becoming a potential competitor for technologies such as QWIP and HgCdTe. Using an empirical tight-binding model, we developed a superlattice design that matches the lattice parameter of GaSb substrates and presents a cutoff wavelength of 12 μm. Electrical and optical measurements performed on single element detectors at 77 K showed an R₀A averaging 13 Ω·cm² and a quantum efficiency as high as 54%. We demonstrated high quality material growth with x-ray FWHM below 30 arcsec and an AFM rms roughness of 1.5 Å over an area of 20x20 μm². A 320x256 array of 25x25μm² pixels, hybridized to an Indigo Read Out Integrated Circuit, performed thermal imaging up to 185 K with an operability close to 97%. The noise equivalent temperature difference at 81 K presented a peak at 270 mK, corresponding to a mean value of 340 mK. [reprint (PDF)]
14.	Background limited performance of long wavelength infrared focal plane arrays fabricated from type-II InAs/GaSb M-structure superlattice P.Y. Delaunay, B.M. Nguyen and M. Razeghi SPIE Porceedings, Vol. 7298, Orlando, FL 2009, p. 72981Q-- April 13, 2009 ...[Visit Journal] Recent advances in growth techniques, structure design and processing have lifted the performance of Type-II InAs/GaSb superlattice photodetectors. The introduction of a M-structure design improved both the dark current and R0A of Type-II photodiodes. This new structure combined with a thick absorbing region demonstrated background limited performance at 77K for a 300K background and a 2-π field of view. A focal plane array with a 9.6 μm 50% cutoff wavelength was fabricated with this design and characterized at 80K. The dark current of individual pixels was measured around 1.3 nA, 7 times lower than previous superlattice FPAs. This led to a higher dynamic range and longer integration times. The quantum efficiency of detectors without anti-reflective coating was 72%. The noise equivalent temperature difference reached 23 mK. The deposition of an anti-reflective coating improved the NEDT to 20 mK and the quantum efficiency to 89%. [reprint (PDF)]
14.	High operating temperature MWIR photon detectors based on Type II InAs/GaSb superlattice M. Razeghi, S. Abdollahi Pour, E.K. Huang, G. Chen, A. Haddadi and B.M. Nguyen SPIE Proceedings, Infrared Technology and Applications XXXVII, Orlando, FL, Vol. 8012, p. 80122Q-1-- April 26, 2011 ...[Visit Journal] Recent efforts have been paid to elevate the operating temperature of Type II superlattice Mid Infrared photon detectors. Using M-structure superlattice, novel device architectures have been developed, resulting in significant improvement of the device performances. In this paper, we will compare different photodetector architectures and discuss the optimization scheme which leads to almost one order of magnitude of improvement to the electrical performance. At 150K, single element detectors exhibit a quantum efficiency above 50%, and a specific detectivity of 1.05x10(12) cm.Hz(1/2)/W. BLIP operation with a 300K background and 2π FOV can be reached with an operating temperature up to 180K. High quality focal plane arrays were demonstrated with a noise equivalent temperature difference (NEDT) of 11mK up to 120K. Human body imaging is achieved at 150K with NEDT of 150mK. [reprint (PDF)]
14.	Optimizing facet coating of quantum cascade lasers for low power consumption Y. Bai, S.R. Darvish, N. Bandyopadhyay, S. Slivken and M. Razeghi Journal of Applied Physics, Vol. 109, No. 5, p. 053103-1-- March 1, 2011 ...[Visit Journal] Typical high power consumption (∼10 W) of mid-infrared quantum cascade lasers (QCLs) has been a serious limitation for applications in battery powered systems. A partial high-reflection (PHR) coating technique is introduced for power downscaling with shorter cavity lengths. The PHR coating consists of a double layer dielectric of SiO₂ and Ge. With this technique, a 4.6 μm QCL with an ultra low threshold power consumption of less than a watt (0.83 W) is demonstrated in room temperature continuous wave operation. At 25°C, the maximum output power and wall plug efficiency are 192 mW and 8.6%, respectively. [reprint (PDF)]
14.	Infrared Imaging Arrays Using Advanced III-V Materials and technology M. Razeghi, J.D. Kim, C. Jelen, S. Slivken, E. Michel, H. Mohseni, J.J. Lee, J. Wojkowski, K.S. Kim, H.I. Jeon, and J. X IEEE Proceedings, Advanced Workshop on Frontiers in Electronics (WOFE), Tenerife, Spain;-- January 6, 1997 ...[Visit Journal] Photodetectors operating in the 3-5 and 8-12 μm atmospheric windows are of great importance for applications in infrared (IR) thermal imaging. HgCdTe has been the dominant material system for these applications. However, it suffers from instability and non-uniformity problems over large areas due to high Hg vapor pressure during the material, growth. There has been a lot of interest in the use of heteroepitaxially grown Sb-based alloys, its strained layer superlattices, and GaAs based quantum wells as alternatives to MCT. This interest has been driven by the advanced material growth and processing technology available for the III-V material system [reprint (PDF)]
14.	Room temperature terahertz quantum cascade laser sources with 215 μW output power through epilayer-down mounting Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai, and M. Razeghi Appl. Phys. Lett. 103, 011101 (2013)-- July 1, 2013 ...[Visit Journal] We report room temperature terahertz (THz) quantum cascade laser sources with high power based on difference frequency generation. The device is Čerenkov phase matched and spectrally purified with an integrated dual-period distributed-feedback grating. Symmetric current injection and epilayer-down mounting of the device onto a patterned submount are used to improve the electrical uniformity and heat removal, respectively. The epilayer-down mounting also allows for THz anti-reflective coating to enhance the THz outcoupling efficiency. Single mode emission at 3.5 THz with a side-mode suppression ratio and output power up to 30 dB and 215 μW are obtained, respectively. [reprint (PDF)]
14.	Temperature dependence of the dark current and activation energy at avalanche onset of GaN Avalanche Photodiodes M.P. Ulmer, E. Cicek, R. McClintock, Z. Vashaei and M. Razeghi SPIE Proceedings, Vol. 8460, p. 84601G-1-- August 15, 2012 ...[Visit Journal] We report a study of the performance of an avalanche photodiode (APD) as a function of temperature from 564 K to 74 K. The dark current at avalanche onset decreases from 564 K to 74 K by approximately a factor of 125 and from 300 K to 74K the dark current at avalanche offset is reduced by a factor of about 10. The drop would have been considerably larger if the activation energy at avalanche onset (Ea) did not also decrease with decreasing temperature. These data give us insights into how to improve the single-photon counting performance of a GaN based ADP. [reprint (PDF)]
14.	Dark current reduction in microjunction-based double electron barrier type-II InAs/InAsSb superlattice long-wavelength infrared photodetectors Romain Chevallier, Abbas Haddadi, & Manijeh Razeghi Scientific Reports 7, Article number: 12617-- October 3, 2017 ...[Visit Journal] Microjunction InAs/InAsSb type-II superlattice-based long-wavelength infrared photodetectors with reduced dark current density were demonstrated. A double electron barrier design was employed to reduce both bulk and surface dark currents. The photodetectors exhibited low surface leakage after passivation with SiO2, allowing the use of very small size features without degradation of the dark current. Fabricating microjunction photodetectors (25 × 25 µm² diodes with 10 × 10 µm² microjunctions) in combination with the double electron barrier design results in a dark current density of 6.3 × 10⁻⁶ A/cm² at 77 K. The device has an 8 µm cut-off wavelength at 77 K and exhibits a quantum efficiency of 31% for a 2 µm-thick absorption region, which results in a specific detectivity value of 1.2 × 10¹² cm·Hz^½/W. [reprint (PDF)]
14.	Comparison of ultraviolet APDs grown on free-standing GaN and sapphire substrates E. Cicek, Z. Vashaei, C. Bayram, R. McClintock, M. Razeghi and M. Ulmer Proceedings, Vol. 7780, p. 77801P, SPIE Optics and Photonics Symposium, Conference on Detectors and Imaging Devices: Infrared, Focal Plane and Single Photon, San Diego, CA -- August 4, 2010 ...[Visit Journal] There is a need for semiconductor-based ultraviolet photodetectors to support avalanche gain in order to realize better performance andmore effective compete with existing technologies. Wide bandgap III-Nitride semiconductors are the promising material system for the development of avalanche photodiodes (APDs) that could be a viable alternative to current bulky UV detectors such as photomultiplier tubes. In this paper, we review the current state-of-the-art in IIINitride visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE. [reprint (PDF)]

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