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1.  InAs quantum dot infrared photodetectors on InP by MOCVD
W. Zhang, H. Lim, M. Taguchi, A. Quivy and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270M -- January 23, 2006 ...[Visit Journal]
We report our recent results of InAs quantum dots grown on InP substrate by low-pressure metalorganic chemical vapor deposition (MOCVD) for the application of quantum dot infrared photodetector (QDIP). We have previously demonstrated the first InP-based QDIP with a peak detection wavelength at 6.4 µm and a detectivity of 1010 cm·Hz½/W at 77K. Here we show our recent work toward shifting the detection wavelength to the 3-5 µm middlewavelength infrared (MWIR) range. The dependence of the quantum dot on the growth conditions is studied by atomic force microscopy, photoluminescence and Fourier transform infrared spectroscopy. Possible ways to increase the quantum efficiency of QDIPs are discussed. [reprint (PDF)]
 
1.  Novel process for direct bonding of GaN onto glass substrates using sacrificial ZnO template layers to chemically lift-off GaN from c-sapphire
Rogers, D. J.; Ougazzaden, A.; Sandana, V. E.; Moudakir, T.; Ahaitouf, A.; Teherani, F. Hosseini; Gautier, S.; Goubert, L.; Davidson, I. A.; Prior, K. A.; McClintock, R. P.; Bove, P.; Drouhin, H.-J.; Razeghi, M.
Proc. SPIE 8263, Oxide-based Materials and Devices III, 82630R (February 9, 2012)-- February 9, 2012 ...[Visit Journal]
GaN was grown on ZnO-buffered c-sapphire (c-Al2O3) substrates by Metal Organic Vapor Phase Epitaxy. The ZnO then served as a sacrificial release layer, allowing chemical lift-off of the GaN from the c-Al2O3 substrate via selective wet etching of the ZnO. The GaN was subsequently direct-wafer-bonded onto a glass substrate. X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray microanalysis, Room Temperature Photoluminescence & optical microscopy confirmed bonding of several mm2 of crack-free wurtzite GaN films onto a soda lime glass microscope slide with no obvious deterioration of the GaN morphology. Using such an approach, InGaN based devices can be lifted-off expensive single crystal substrates and bonded onto supports with a better cost-performance profile. Moreover, the approach offers the possibility of reclaiming and reusing the substrate. [reprint (PDF)]
 
1.  Ammonium Sulfide Passivation of Type-II InAs/GaSb Superlattice Photodiodes
A. Gin, Y. Wei, A. Hood, A. Bajowala, V. Yazdanpanah, M. Razeghi and M.Z. Tidrow
Applied Physics Letters, 84 (12)-- March 22, 2004 ...[Visit Journal]
We report on the surface passivation of Type-II InAs/GaSb superlattice photodetectors using various ammonium sulfide solutions. Compared to unpassivated detectors, zero-bias resistance of treated 400 µm×400 µm devices with 8 µm cutoff wavelength was improved by over an order of magnitude to ~20 kΩ at 80 K. Reverse-bias dark current density was reduced by approximately two orders of magnitude to less than 10 mA/cm2 at –2 V. Dark current modeling, which takes into account trap-assisted tunneling, indicates greater than 70 times reduction in bulk trap density for passivated detectors. [reprint (PDF)]
 
1.  Thermal Conductivity of InAs/GaSb Type II Superlattice
C. Zhou, B.M. Nguyen, M. Razeghi and M. Grayson
Journal of Electronic Materials, Vol. 41, No. 9, p. 2322-2325-- August 1, 2012 ...[Visit Journal]
The cross-plane thermal conductivity of a type II InAs/GaSb superlattice(T2SL) is measured from 13 K to 300 K using the 3x method. Thermal conductivity is reduced by up to two orders of magnitude relative to the GaSb bulk substrate. The low thermal conductivity of around 1 W/m K to 8 W/m K may serve as an advantage for thermoelectric applications at low temperatures, while presenting a challenge for T2SL interband cascade lasers and highpower photodiodes. We describe a power-law approximation to model nonlinearities in the thermal conductivity, resulting in increased or decreased peak temperature for negative or positive exponents, respectively. [reprint (PDF)]
 
1.  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·Hz1/2/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)]
 
1.  InP-based quantum-dot infrared photodetectors with high quantum efficiency and high temperature imaging
S. Tsao, H. Lim, H. Seo, W. Zhang and M. Razeghi
IEEE Sensors Journal, Vol. 8, No. 6, p. 936-941-- June 1, 2008 ...[Visit Journal]
We report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metalorganic chemical vapor depositon. The detectivity was 6 x 1010cm·Hz1/2·W-1 at 150 K and a bias of 5 V with a peak detection wavelength around 4.0 micron and a quantum efficiency of 48%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature. A 320 x 256 middle wavelength infrared focal plane array operating at temperatures up to 200 K was also demonstrated. The focal plane array had 34 mA/W responsivity, 1.1% conversion efficiency, and noise equivalent temperature difference of 344 mK at 120 K operating temperature. [reprint (PDF)]
 
1.  Focal plane arrays based on quantum dot infrared photodetectors
Manijeh Razeghi; Wei Zhang; Ho-Chul Lim; Stanley Tsao; John Szafraniec; Maho Taguchi; Bijan Movaghar
Proc. SPIE 5838, Nanotechnology II, 125 (June 28, 2005);-- June 28, 2005 ...[Visit Journal]
Here we report the first demonstrations of infrared focal plane array (FPA) based on GaAs and InP based quantum dot infrared photodetectors (QDIPs). QDIPs are extension of quantum well infrared photodetectors (QWIPs) and are predicted to outperform QWIPs due to their potential advantages including normally incident absorption, higher responsivity and high temperature operation. Two material systems have been studied: InGaAs/InGaP QDIPs on GaAs substrates and InAs QDIP on InP substrates. An InGaAs/InGaP QDIP has been grown on GaAs substrate by LP-MOCVD. Photoresponse was observed at temperatures up to 200 K with a peak wavelength of 4.7 μm and cutoff wavelength of 5.2 μm. A detectivity of 1.2x1011 cm·Hz1/2/W was obtained at T=77 K and bias of -0.9 V, which is the highest for QDIPs grown by MOCVD. An InAs QDIP structure has also been grown on InP substrate by LP-MOCVD. Photoresponse of normal incidence was observed at temperature up to 160K with a peak wavelength of 6.4 μm and cutoff wavelength of 6.6 μm. A detectivity of 1.0x1010 cm·Hz1/2/W was obtained at 77K at biases of -1.1 V, which is the first and highest detectivity reported for QDIP on InP substrate. 256×256 detector arrays were fabricated first time in the world for both the GaAs and InP based QDIPs. Dry etching and indium bump bonding were used to hybridize the arrays to a Litton readout integrated circuit. For the InGaAs/InGaP QDIP FPA, thermal imaging was achieved at temperatures up to 120 K. At T=77K, the noise equivalent temperature difference (NEDT) was measured as 0.509K with a 300K background and f/2.3 optics. For the InP based QDIPs, thermal imaging was achieved at 77 K. [reprint (PDF)]
 
1.  Advances in UV sensitive visible blind GaN-based APDs
M. Ulmer, R. McClintock and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7945, p. 79451G-- January 23, 2011 ...[Visit Journal]
In this paper, we describe our current state-of-the-art process of making visible-blind APDs based on GaN. We have grown our material 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 are compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes. Single photon detection capabilities with over 30% are demonstrated. We show how with pulse height discrimination the Geiger-mode operation conditions can be optimized for enhanced SPDE versus dark counts. [reprint (PDF)]
 
1.  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)]
 
1.  High power 1D and 2D photonic crystal distributed feedback quantum cascade lasers
B. Gokden, Y. Bai, S. Tsao, N. Bandyopadhyay, S. Slivken and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7945, p. 79450C-- January 23, 2011 ...[Visit Journal]
For many practical applications that need bright sources of mid-infrared radiation, single mode operation and good beam quality are also required. Quantum cascade lasers are prominent candidates as compact sources of mid-infrared radiation capable of delivering very high power both CW and under pulsed operation. While 1D photonic crystal distributed feedback structures can be used to get single mode operation from quantum cascade lasers with narrow ridge widths, novel 2D photonic crystal cavity designs can be used to improve spectral and spatial purity of broad area quantum cascade lasers. In this paper, we demonstrate high power, spatially and spectrally pure operation at room temperature from narrow ridge and broad area quantum cascade lasers with buried 1D and 2D photonic crystal structures. Single mode continuous wave emission at λ = 4.8 μm up to 700 mW in epi-up configuration at room temperature was observed from a 11 μm wide 5 mm long distributed feedback quantum cascade laser with buried 1D gratings. High peak powers up to 34 W was obtained from a 3mm long 400 μm wide 2D photonic crystal distributed feedback laser at room temperature under pulsed operation. The far field profile had a single peak normal to the laser facet and the M2 figure of merit was as low as 2.5. Emission spectrum had a dominating single mode at λ = 4.36 μm. [reprint (PDF)]
 
1.  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)]
 
1.  Radiometric characterization of long-wavelength infrared type II strained layer superlattice focal plane array under low-photon irradiance conditions
J. Hubbs, V. Nathan, M. Tidrow, and M. Razeghi
Optical Engineering, Vol. 51, No. 6, p. 064002-1-- June 15, 2012 ...[Visit Journal]
We present the results of the radiometric characterization of an “M” structure long wavelength infrared Type-II strained layer superlattice(SLS) infrared focal plane array (IRFPA) developed by Northwestern University (NWU). The performance of the M-structure SLS IRFPA was radiometrically characterized as a function of photon irradiance, integration time, operating temperature, and detector bias. Its performance is described using standard figures of merit: responsivity, noise, and noise equivalent irradiance. Assuming background limited performance operation at higher irradiances, the detector quantum efficiency for the SLS detector array is approximately 57%. The detector dark density at 80 K is 142 μA∕cm², which represents a factor of seven reduction from previously measured devices. [reprint (PDF)]
 
1.  Continuous operation of a monolithic semiconductor terahertz source at room temperature
Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai, and M. Razeghi
Appl. Phys. Lett. 104, 221105 (2014)-- June 3, 2014 ...[Visit Journal]
We demonstrate room temperature continuous wave THz sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers. Buried ridge, buried composite distributed-feedback waveguide with Čerenkov phase-matching scheme is used to reduce the waveguide loss and enhance the heat dissipation for continuous wave operation. Continuous emission at 3.6 THz with a side-mode suppression ratio of 20 dB and output power up to 3 μW are achieved, respectively. THz peak power is further scaled up to 1.4 mW in pulsed mode by increasing the mid-infrared power through increasing the active region doping and device area. [reprint (PDF)]
 
1.  Chemical lift-off and direct wafer bonding of GaN/InGaN P-I-N structures grown on ZnO
K. Pantzas, D.J. Rogers, P. Bove, V.E. Sandana, F.H. Teherani, Y. El Gmili, M. Molinari, G. Patriarche, L. Largeau, O. Mauguin, S. Suresh, P.L. Voss, M. Razeghi, A. Ougazzaden
Journal of Crystal Growth -- November 7, 2015 ...[Visit Journal]
p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscopy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process. [reprint (PDF)]
 
1.  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)]
 
1.  High Detectivity InAs Quantum-Dot Infrared Photodetectors Grown on InP by Metalorganic Chemical Vapor Deposition
W. Zhang, H. Lim, M. Taguchi, S. Tsao, B. Movaghar, and M. Razeghi
Applied Physics Letters, 86 (19)-- May 9, 2005 ...[Visit Journal]
We report a high-detectivity InAs quantum-dot infrared photodetector. The InAs quantum dots were grown by self-assembly on InP substrates via low-pressure metal–organic chemical–vapor deposition. Highly uniform quantum dots with a density of 4×1010 cm2 were grown on a GaAs/InP matrix. Photoresponse was observed at temperatures up to 160 K with a peak of 6.4 µm and cutoff of 6.6 µm. Very low dark currents and noise currents were obtained by inserting Al0.48In0.52As current blocking layers. The background-limited performance temperature was 100 K. A detectivity of 1.0×1010 cm·Hz½/W was obtained at 77 K with a bias of –1.1 V. [reprint (PDF)]
 
1.  III-Nitride Optoelectronic Devices: From ultraviolet detectors and visible emitters towards terahertz intersubband devices
M. Razeghi, C. Bayram, Z. Vashaei, E. Cicek and R. McClintock
IEEE Photonics Society 23rd Annual Meeting, November 7-10, 2010, Denver, CO, Proceedings, p. 351-352-- January 20, 2011 ...[Visit Journal]
III-nitride optoelectronic devices are discussed. Ultraviolet detectors and visible emitters towards terahertz intersubband devices are reported. Demonstration of single photon detection efficiencies of 33% in the ultraviolet regime, intersubband energy level as low as in the mid-infrared regime, and GaN-based resonant tunneling diodes with negative resistance of 67 Ω are demonstrated. [reprint (PDF)]
 
1.  High performance quantum dot-quantum well infrared focal plane arrays
S. Tsao, A. Myzaferi, and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7605, p. 76050J-1-- January 27, 2010 ...[Visit Journal]
Quantum dot (QD) devices are a promising technology for high operating temperature detectors. We have studied InAs QDs embedded in an InGaAs/InAlAs quantum well structure on InP substrate for middle wavelength infrared detectors and focal plane arrays (FPAs). This combined dot-well structure has weak dot confinement of carriers, and as a result, the device behavior differs significantly from that in more common dot systems with stronger confinement. We report on our studies of the energy levels in the QDWIP devices and on QD-based detectors operating at high temperature with D* over 1010 cm·Hz½/W at 150 K operating temperature and high quantum efficiency over 50%. FPAs have been demonstrated operating at up to 200 K. We also studied two methods of adapting the QDWIP device to better accommodate FPA readout circuit limitations. [reprint (PDF)]
 
1.  Demonstration of shortwavelength infrared photodiodes based on type-II InAs/GaSb/AlSb superlattices
A.M. Hoang, G. Chen, A. Haddadi, S. Abdollahi Pour, and M. Razeghi
Applied Physics Letters, Vol. 100, No. 21, p. 211101-1-- May 21, 2012 ...[Visit Journal]
We demonstrate the feasibility of the InAs/GaSb/AlSb type-II superlattice photodiodes operating at the short wavelength infrared regime below 3  μm. An n-i-p type-II InAs/GaSb/AlSb photodiode was grown with a designed cut-off wavelength of 2 μm on a GaSb substrate. At 150  K, the photodiode exhibited a dark current density of 5.6 × 10−8 A/cm² and a front-side-illuminated quantum efficiency of 40.3%, providing an associated shot noise detectivity of 1.0 × 1013 Jones. The uncooled photodiode showed a dark current density of 2.2 × 10−3 A/cm² and a quantum efficiency of 41.5%, resulting in a detectivity of 1.7 × 1010 Jones [reprint (PDF)]
 
1.  ZnO nanorod electrodes for hydrogen evolution and storage
Harinipriya, S.; Usmani, B.; Rogers, D. J.; Sandana, V. E.; Teherani, F. Hosseini; Lusson, A.; Bove, P.; Drouhin, H.-J.; Razeghi, M.
Proc. SPIE 8263, Oxide-based Materials and Devices III, 82631Y (February 9, 2012)-- February 9, 2012 ...[Visit Journal]
Due to the attractive combination of a relatively high specific heat of combustion with a large specific energy capacity, molecular hydrogen (H2) is being investigated for use as an alternative to fossil fuels. Energy-efficient H2 production and safe storage remain key technical obstacles to implementation of an H2 based economy, however. ZnO has been investigated for use as an alternative photocatalytic electrode to TiO2 for solarpowered photo-electro-chemical (PEC) electrolysis, in which H2 is generated by direct water splitting in a cell with a metal cathode and a semiconducting anode. In this investigation, ZnO NR grown on Si (100) substrates by pulsed laser deposition were investigated for use as electrodes in the Hydrogen Evolution Reaction (HER). The electrochemical potential and Fermi energy of the ZnO NR were estimated from the electrochemical current density in acid and alkaline solutions via phenomenological thermodynamic analysis. As well as acting as an effective electrocalytic cathode, the ZnO NR appear to operate as a hydrogen reservoir. These results indicate that the ZnO NR have excellent potential for the storage of evolved H2. [reprint (PDF)]
 
1.  Recent performance records for mid-IR quantum cascade lasers
M. Razeghi; Y. Bai; S. Slivken; S. Kuboya; S.R. Darvish
Terahertz and Mid Infrared Radiation: Basic Research and Practical Applications, 2009. TERA-MIR International Workshop [5379656], (2009) -- November 9, 2009 ...[Visit Journal]
The wall plug efficiency of the mid-infrared quantum cascade laser in room temperature continuous wave operation is brought to 17%. Peak output power from a broad area (400 μm x 3 mm) device gives 120 W output power in pulsed mode operation at room temperature. Using a single-well-injector design, specifically made for low temperature operation, a record wall plug efficiency of 53% is demonstrated at 40 K. [reprint (PDF)]
 
1.  High performance InAs quantum dot infrared photodetectors (QDIP) on InP by MOCVD
W. Zhang, H. Lim, M. Taguchi, S. Tsao, J. Szafraniec, B. Movaghar, M. Razeghi, and M. Tidrow
SPIE Conference, Jose, CA, Vol. 5732, pp. 326-- January 22, 2005 ...[Visit Journal]
Inter-subband detectors such as quantum well infrared photodetectors (QWIP) have been widely used in infrared detection. Quantum dot infrared photodetectors (QDIPs) have been predicted to have better performance than QWIPs including higher operation temperature and normal incidence detection. Here we report our recent results of InAs QDIP grown on InP substrate by low-pressure metalorganic chemical vapor deposition (MOCVD). The device structures consist of multiple stacks of InAs quantum dots with InP barriers. High detectivities in the range of 1010cm·Hz1/2/W were obtained at 77K. The measurements at higher temperatures show better temperature dependent performance than QWIP. However, the performances of QDIPs are still far from the expected. One of the reasons is the low quantum efficiency due to the low fill factor of quantum dots layer. Resonant cavity enhanced QDIP has been studied to increase the quantum efficiency. Different schemes of mirrors using free carrier plasma and distributed Bragg reflector are discussed. [reprint (PDF)]
 
1.  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)]
 
1.  High operability 1024 x 1024 long wavelength Type-II superlattice focal plane array
A. Haddadi, S.R. Darvish, G. Chen, A.M. Hoang, B.M. Nguyen and M. Razeghi
IEEE Journal of Quantum Electronics (JQE), Vol. 48, No. 2, p. 221-228-- February 10, 2012 ...[Visit Journal]
Electrical and radiometric characterization results of a high-operability 1024 x 1024 long wavelength infrared type-II superlattice focal plane array are described. It demonstrates excellent quantum efficiency operability of 95.8% and 97.4% at operating temperatures of 81 K and 68 K, respectively. The external quantum efficiency is 81% without any antireflective coating. The dynamic range is 37 dB at 81 K and increases to 39 dB at 68 K operating temperature. The focal plane array has noise equivalent temperature difference as low as 27 mK and 19 mK at operating temperatures of 81 K and 68 K, respectively, using f/2 optics and an integration time of 0.13 ms. [reprint (PDF)]
 
1.  High power operation of λ ∼ 5.2–11 μm strain balanced quantum cascade lasers based on the same material composition
N. Bandyopadhyay, Y. Bai, S. Slivken, and M. Razeghi
Appl. Phys. Lett. 105, 071106 (2014)-- August 20, 2014 ...[Visit Journal]
A technique based on composite quantum wells for design and growth of strain balanced Al0.63In0.37As/Ga0.35In0.65As/Ga0.47In0.53As quantum cascade lasers (QCLs) by molecular beam epitaxy (MBE), emitting in 5.2–11 μm wavelength range, is reported. The strained Al0.63In0.37As provides good electron confinement at all wavelengths, and strain balancing can be achieved through composite wells of Ga0.35In0.65As/Ga0.47In0.53As for different wavelength. The use of these fixed composition materials can avoid the need for frequent calibration of a MBE reactor to grow active regions with different strain levels for different wavelengths. Experimental results for QCLs emitting at 5.2, 6.7, 8.2, 9.1, and 11 μm exhibit good wall plug efficiencies and power across the whole wavelength range. It is shown that the emission wavelength can be predictably changed using the same design template. These lasers are also compatible with a heterogeneous broadband active region, consisting of multiple QCL cores, which can be produced in a single growth run. [reprint (PDF)]
 

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