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1.  Substrate removal for high quantum efficiency back side illuminated type-II InAs/GaSb photodetectors
P.Y. Delaunay, B.M. Nguyen, D. Hoffman and M. Razeghi
Applied Physics Letters, Vol. 91, No. 23, p. 231106-- December 3, 2007 ...[Visit Journal]
A substrate removal technique using an InAsSb etch stop layer improves by a factor of 2 the quantum efficiency of back side illuminated type-II InAs/GaSb superlattice photodetectors. After etching of the GaSb substrate with a CrO3 based solution, the quantum efficiency of the diodes presents Fabry-Pérot oscillations averaging at 56%. Due to the confinement of the infrared light inside the devices, the quantum efficiency for certain devices reaches 75% at 8.5 µm. The implementation of this new technique to a focal plane array resulted in a decrease of the integration time from 0.23 to 0.08 ms. [reprint (PDF)]
 
1.  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)]
 
1.  4.5 mW Operation of AlGaN-based 267 nm Deep-Ultraviolet Light-Emitting Diodes
A. Yasan, R. McClintock, K. Mayes, D. Shiell, L. Gautero, S.R. Darvish, P. Kung and M. Razeghi
Applied Physics Letters, 83 (23)-- December 8, 2003 ...[Visit Journal]
We demonstrate 4.5 mW output power from AlGaN-based single quantum well ultraviolet light-emitting diodes at a very short wavelength of 267 nm in pulsed operation mode. The output power in continuous-wave mode reaches a value of 165 µW at an injected current of 435 mA. The measurements were done on arrays of four devices flip chip bonded to AlN submounts for thermal management. [reprint (PDF)]
 
1.  Advances in APDs for UV astronomy
Melville P. Ulmer; Ryan M. McClintock; Jose L. Pau; Manijeh Razeghi
Proc. SPIE 6686, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XV, 668605 (September 13, 2007)-- November 13, 2007 ...[Visit Journal]
We report the most recent work of our group of the development of avalanche photo diodes based on (Al)GaN. The goal of this group is to achieve single photon counting. In this paper we first give the scientific motivation for making such a device in the context of UV astronomy and then describe current work and plans for future development. The development includes improving the sensitivity to be able to carry out single photon detection and the fabrication of arrays. [reprint (PDF)]
 
1.  Demonstration of 256x256 Focal Plane Arrays Based on Al-free GaInAs/InP QWIP
J. Jiang, K. Mi, R. McClintock, M. Razeghi, G.J. Brown, and C. Jelen
IEEE Photonics Technology Letters 15 (9)-- September 1, 2003 ...[Visit Journal]
We report the first demonstration of an infrared focal plane array based on aluminum-free GaInAs-InP quantum-well infrared photodetectors (QWIPs).A unique positive lithography method was developed to perform indium-bump liftoff. The noise equivalent differential temperature (NEΔT) of 29 mK was achieved at 70 K with f/2 optics. [reprint (PDF)]
 
1.  On the interface properties of ZnO/Si electroluminescent diodes
J.L. Pau, J. Piqueras, D.J. Rogers, F. Hosseini Teherani, K. Minder, R. McClintock, and M. Razeghi
Journal of Applied Physics, Vol. 107, No. 3, p. 033719-1-- February 1, 2010 ...[Visit Journal]
ZnO layers grown on n–Si(100), n+–Si(100), and n–Si(111) substrates by pulsed-laser deposition were found to give electroluminescence. Light emission was observed in the form of discrete spots for currents over 1 mA with a white appearance to the naked eye. The intensity of these spots showed an erratic behavior over time, appearing and disappearing at random, while showing an associated random telegraph noise in the current signal. Regardless the substrate used, the electroluminescence spectra had a main broadband emission centered at about 600 nm and a relatively small peak at around 380 nm which corresponds to the energy of ZnO near band edge emission. Furthermore, the devices exhibited rectifying characteristics, whose current blocking direction depended on the substrate orientation. Optimization of ZnO conductivity and performing sample growth in N2 ambient were found to be critical to enhance the emission intensity. Rutherford backscattering characterization revealed the existence of an intermixed region at the interface between ZnO and Si. To study the electronic properties at the interface, frequency dependent capacitance measurements were carried out. The junction capacitance became frequency dependent at the bias voltages at which light emission occurs due to the relatively slow trapping and generation processes at deep centers. These centers are believed to play an important role in the mechanism of light emission. [reprint (PDF)]
 
1.  Research activity on Type-II InAs/GaSb superlattice for LWIR detection and imaging at the Center for Quantum Devices
M. Razeghi and B.M. Nguyen
American Institute of Physics Conference Proceedings Vol. 949, Issue 1, p. 35-42, 6th International Workshop on Information Optics (WIO'07), Reykjavik, Iceland, June 25-30, 2007-- October 24, 2007 ...[Visit Journal]
Type-II superlattice photodetectors have recently experienced significant improvements in both theoretical structure design and experimental realization. Empirical Tight Binding Method was initiated and developed for Type-II superlattice. A new Type-II structure, called M-structure, was introduced and theoretically demonstrated high R0A, high quantum efficiency. Device design and growth condition were optimized to improve the performance. As a result, a 54% quantum efficiency, a 12 Ω·cm2 R0A were achieved for 11 µm cut-off photodetector at 77 K. Effective surface passivation techniques for MWIR and LWIR Type-II superlattice were developed. FPA imaging at MWIR and LWIR were demonstrated with a capability of imaging up to room temperature and 211 K respectively. The noise equivalent temperature difference presented a peak at 50 mK for MWIR FPA at 121 K and 26 mK for LWIR FPA at 81 K. [reprint (PDF)]
 
1.  A Crystallographic Model of (00*1) Aluminum Nitride Epitaxial Thin Film Growth on (00*1) Sapphire Substrate
C.J. Sun, P. Kung, A. Saxler, H. Ohsato, M. Razeghi, and K. Haritos
Journal of Applied Physics 75 (8)-- April 15, 1994 ...[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 (011-bar 2) sapphire substrates by metalorganic chemical vapor deposition. Better crystallinity with fine ridgelike facets is obtained on the (011-bar 2) sapphire. Also lower carrier concentration and higher mobilities indicate both lower nitrogen vacancies and less oxygen incorporation on the (011-bar 2) sapphire. The results of this study show better physical properties of GaN thin films achieved on (011-bar 2) sapphire. [reprint (PDF)]
 
1.  Growth of In1-xTlxSb, a New Infrared Material, by Low-Pressure Metalorganic Chemical Vapor Deposition
Y.H. Choi, R. Sudharsanan, C, Besikci, and M. Razeghi
Applied Physics Letters 63 (3)-- July 19, 1993 ...[Visit Journal]
We report the growth of In1-xTlxSb, a new III-V alloy for long-wavelength infrared detector applications, by low-pressure metalorganic chemical vapor deposition. In1-xTlxSb with good surface morphology was obtained on both GaAs and InSb substrates at a growth temperature of 455 °C. X-ray diffraction measurements showed resolved peaks of In1-xTlxSb and InSb films. Infrared absorption spectrum of In1-xTlxSb showed a shift toward lower energies compared to InSb spectrum. Hall mobility data on In1-xTlxSb/InSb/GaAs structure showed enhanced mobility at low temperatures compared to InSb/GaAs structure. [reprint (PDF)]
 
1.  High-Performance InP-Based Mid-IR Quantum Cascade Lasers
M. Razeghi
IEEE Journal of Selected Topics in Quantum Electronics, Vol. 15, No. 3, May-June 2009, p. 941-951.-- June 5, 2009 ...[Visit Journal]
Quantum cascade lasers (QCLs) were once considered as inefficient devices, as the wall-plug efficiency (WPE) was merely a few percent at room temperature. But this situation has changed in the past few years, as dramatic enhancements to the output power andWPE have been made for InP-based mid-IR QCLs. Room temperature continuous-wave (CW) output power as high as 2.8 W and WPE as high as 15% have now been demonstrated for individual devices. Along with the fundamental exploration of refining the design and improving the material quality, a consistent determination of important device performance parameters allows for strategically addressing each component that can be improved potentially. In this paper, we present quantitative experimental evidence backing up the strategies we have adopted to improve the WPE for QCLs with room temperature CW operation. [reprint (PDF)]
 
1.  Beryllium compensation doping of InAs/GaSb infrared superlattice photodiodes
D. Hoffman, B.M. Nguyen, P.Y. Delaunay, A. Hood, M. Razeghi and J. Pellegrino
Applied Physics Letters, Vol. 91, No. 14, p. 143507-1-- October 1, 2007 ...[Visit Journal]
Capacitance-voltage measurements in conjunction with dark current measurements on InAs/GaSb long wavelength infrared superlattice photodiodes grown by molecular-beam epitaxy on GaSb substrates are reported. By varying the beryllium concentration in the InAs layer of the active region, the residually n-type superlattice is compensated to become slightly p-type. By adjusting the doping, the dominant dark current mechanism can be varied from diffusion to Zener tunneling. Minimization of the dark current leads to an increase of the zero-bias differential resistance from less than 4 to 32 cm2 for a 100% cutoff of 12.05 µm [reprint (PDF)]
 
1.  Demonstration of a 256x256 Middle-Wavelength Infrared Focal Plane Array based on InGaAs/InGaP Quantum Dot Infrared Photodetectors (QDIPs)
J. Jiang, K. Mi, S. Tsao, W. Zhang, H. Lim, T.O'Sullivan, T. Sills, M. Razeghi, G.J. Brown, and M.Z. Tidrow
Virtual Journal of Nanoscale Science and Technology 9 (13)-- April 5, 2004 ...[Visit Journal][reprint (PDF)]
 
1.  Type-II superlattice photodetectors for MWIR to VLWIR focal plane arrays
M. Razeghi, Y. Wei, A. Hood, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E. Michel and R. McClintock
SPIE Infrared Technology and Applications Conference, April 17-21, 2006, Orlando, FL Proceedings – Infrared Technology and Applications XXXII, Vol. 6206, p. 62060N-1-- April 21, 2006 ...[Visit Journal]
Results obtained on GaSb/InAs Type-II superlattices have shown performance comparable to HgCdTe detectors, with the promise of higher performance due to reduced Auger recombination and dark current through improvements in device design and material quality. In this paper, we discuss advancements in Type-II IR sensors that cover the 3 to > 30 µm wavelength range. Specific topics covered will be device design and modeling using the Empirical Tight Binding Method (ETBM), material growth and characterization, device fabrication and testing, as well as focal plane array processing and imaging. Imaging has been demonstrated at room temperature for the first time with a 5 µm cutoff wavelength 256×256 focal plane array. [reprint (PDF)]
 
1.  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)]
 
1.  Growth of AlGaN on silicon substrates: a novel way to make back-illuminated ultraviolet photodetectors
Ryan McClintock ; Manijeh Razeghi
Proc. SPIE 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications, 95550U-- August 28, 2015 ...[Visit Journal]
AlGaN, with its tunable wide-bandgap is a good choice for the realization of ultraviolet photodetectors. AlGaN films tend to be grown on foreign substrates such as sapphire, which is the most common choice for back-illuminated devices. However, even ultraviolet opaque substrates like silicon holds promise because, silicon can be removed by chemical treatment to allow back-illumination,1 and it is a very low-cost substrate which is available in large diameters up to 300 mm. However, Implementation of silicon as the solar-blind PD substrates requires overcoming the lattice-mismatch (17%) with the AlxGa1-xN that leads to high density of dislocation and crack-initiating stress. In this talk, we report the growth of thick crack-free AlGaN films on (111) silicon substrates through the use of a substrate patterning and mask-less selective area regrowth. This technique is critical as it decouples the epilayers and the substrate and allows for crack-free growth; however, the masking also helps to reduce the dislocation density by inclining the growth direction and encouraging dislocations to annihilate. A back-illuminated p-i-n PD structure is subsequently grown on this high quality template layer. After processing and hybridizing the device we use a chemical process to selectively remove the silicon substrate. This removal has minimal effect on the device, but it removes the UV-opaque silicon and allows back-illumination of the photodetector. We report our latest results of back-illuminated solar-blind photodetectors growth on silicon. [reprint (PDF)]
 
1.  Polarity inversion of Type-II InAs/GaSb superlattice photodiodes
B.M. Nguyen, D. Hoffman, P.Y. Delaunay, M. Razeghi and V. Nathan
Applied Physics Letters, Vol. 91, No. 10, p. 103503-1-- September 3, 2007 ...[Visit Journal]
The authors demonstrated the realization of p-on-n Type-II InAs/GaSb superlattice photodiodes. Growth condition for high quality InAsSb layer lattice matched to GaSb was established for the use of an effective n-contact layer. By studying the effect of various GaSb capping layer thicknesses on the optical and electrical performances, an optimized thickness of 160 nm was determined. In comparison to as grown n-on-p superlattice photodiodes, this inverted design of p on n has shown similar quality. Finally, by analyzing Fabry-Perot interference fringes in the front side illuminated spectral measurement, the refractive index of the superlattice was determined to be approximately 3.8. [reprint (PDF)]
 
1.  Type-II Superlattices and Quantum Cascade Lasers for MWIR and LWIR Free-Space Communications
A. Hood, A. Evans and M. Razeghi
SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 690005-1-9.-- February 1, 2008 ...[Visit Journal]
Free-space optical communications has recently been touted as a solution to the "last mile" bottleneck of high-speed data networks providing highly secure, short to long range, and high-bandwidth connections. However, commercial near infrared systems experience atmospheric scattering losses and scintillation effects which can adversely affect a link's operating budget. By moving the operating wavelength into the mid- or long-wavelength infrared enhanced link uptimes and increased operating range can be achieved due to less susceptibility to atmospheric affects. The combination of room-temperature, continuous-wave, high-power quantum cascade lasers and high operating temperature type-II superlattice photodetectors offers the benefits of mid- and long-wavelength infrared systems as well as practical operating conditions for next generation free-space communications systems. [reprint (PDF)]
 
1.  High Quality Aluminum Nitride Epitaxial Layers Grown on Sapphire Substrates
A. Saxler, P. Kung, C.J. Sun, E. Bigan and M. Razeghi
Applied Physics Letters 64 (3)-- January 17, 1994 ...[Visit Journal]
In this letter we report the growth of high quality AlN epitaxial layers on sapphire substrates. The AlN grown on (00·1) sapphire exhibited a better crystalline quality than that grown on (01·2) sapphire. An x-ray rocking curve of AlN on (00·1) Al2O3 yielded a full width at half-maximum of 97.2 arcsec, which is the narrowest value reported to our knowledge. The AlN peak on (01·2) Al2O3 was about 30 times wider. The absorption edge measured by ultraviolet transmission spectroscopy for AlN grown on (00·1) Al2O3 was about 197 nm. [reprint (PDF)]
 
1.  Core-shell GaN-ZnO Moth-eye Nanostructure Arrays Grown on a-SiO2/Si (111) as a basis for Improved InGaN-based Photovoltaics and LEDs
D.J. Rogers, V.E. Sandana, S. Gautier, T. Moudakir, M. Abid, A. Ougazzaden, F. Hosseini Teherani, P. Bove, M. Molinari, M. Troyon, M. Peres, Manuel J. Soares, A.J. Neves, T. Monteiro, D. McGrouther, J.N. Chapman, H.-J. Drouhin, R. McClintock, M. Razeghi
Photonics and Nanostructures - Fundamentals and Applications (2015)-- March 30, 2015 ...[Visit Journal]
Self-forming, vertically-aligned, ZnO moth-eye-like nanoarrays were grown by catalyst-free pulsed laser deposition on a-SiO2/Si (111) substrates. X-Ray Diffraction (XRD) and Cathodoluminescence (CL) studies indicated that nanostructures were highly c-axis oriented wurtzite ZnO with strong near band edge emission. The nanostructures were used as templates for the growth of non-polar GaN by metal organic vapor phase epitaxy. XRD, scanning electron microscopy, energy dispersive X-ray microanalysis and CL revealed ZnO encapsulated with GaN, without evidence of ZnO back-etching. XRD showed compressive epitaxial strain in the GaN, which is conducive to stabilization of the higher indium contents required for more efficient green light emitting diode (LED) and photovoltaic (PV) operation. Angular-dependent specular reflection measurements showed a relative reflectance of less than 1% over the wavelength range of 400–720 nm at all angles up to 60°. The superior black-body performance of this moth-eye-like structure would boost LED light extraction and PV anti-reflection performance compared with existing planar or nanowire LED and PV morphologies. The enhancement in core conductivity, provided by the ZnO, would also improve current distribution and increase the effective junction area compared with nanowire devices based solely on GaN. [reprint (PDF)]
 
1.  Room temperature continuous wave operation of λ ~ 3-3.2 μm quantum cascade lasers
N. Bandyopadhyay, Y. Bai, S. Tsao, S. Nida, S. Slivken and M. Razeghi
Applied Physics Letters, Vol. 101, No. 24, p. 241110-1-- December 10, 2012 ...[Visit Journal]
We demonstrate quantum cascade lasers emitting at wavelengths of 3–3.2 μm in the InP-based material system. The laser core consists of GaInAs/AlInAs using strain balancing technique. In room temperature pulsed mode operation, threshold current densities of 1.66 kA∕cm² and 1.97 kA∕cm², and characteristic temperatures (T0) of 108 K and 102 K, are obtained for the devices emitting at 3.2 μm and 3 μm, respectively. Room temperature continuous wave operation is achieved at both wavelengths. [reprint (PDF)]
 
1.  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)]
 
1.  Gain and recombination dynamics of quantum-dot infrared photodetecto
H. Lim, B. Movaghar, S. Tsao, M. Taguchi, W. Zhang, A.A. Quivy, and M. Razeghi
Virtual Journal of Nanoscale Science & Technology-- December 4, 2006 ...[Visit Journal][reprint (PDF)]
 
1.  AlxGa1-xN-based back-illuminated solar-blind photodetectors with external quantum efficiency of 89%
E. Cicek, R. McClintock, C. Y. Cho, B. Rahnema, and M. Razeghi
Appl. Phys. Lett. 103, 191108 (2013)-- November 5, 2013 ...[Visit Journal]
We report on high performance AlxGa1−xN-based solar-blind ultraviolet photodetector (PD) array grown on sapphire substrate. First, high quality, crack-free AlN template layer is grown via metalorganic chemical vapor deposition. Then, we systematically optimized the device design and material doping through the growth and processing of multiple devices. After optimization, uniform and solar-blind operation is observed throughout the array; at the peak detection wavelength of 275 nm, 729 μm² area PD showed unbiased peak external quantum efficiency and responsivity of ∼80% and ∼176 mA/W, respectively, increasing to 89% under 5 V of reverse bias. Taking the reflection loses into consideration, the internal quantum efficiency of these optimized PD can be estimated to be as high as ∼98%. The visible rejection ratio measured to be more than six orders of magnitude. Electrical measurements yielded a low-dark current density: <2 × 10−9 A/cm², at 10 V of reverse bias. [reprint (PDF)]
 
1.  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)]
 
1.  Modeling of Type-II InAs/GaSb Superlattices Using Empirical Tight-Binding Method and Interface Engineering
Y. Wei and M. Razeghi
Physical Review B, 69 (8)-- February 15, 2004 ...[Visit Journal]
We report the most recent work on the modeling of type-II InAs/GaSb superlattices using the empirical tight binding method in an sp3s* basis. After taking into account the antimony segregation in the InAs layers, the modeling accuracy of the band gap has been improved. Our calculations agree with our experimental results within a certain growth uncertainty. In addition, we introduce the concept of GaxIn1-x type interface engineering in order to reduce the lattice mismatch between the superlattice and the GaSb (001) substrate to improve the overall superlattice material quality. [reprint (PDF)]
 

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