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1.  Growth and characterization of long wavelength infrared Type-II superlattice Photodiodes on a 3
B.M. Nguyen, G. Chen, M.A. Hoang, and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7945, p. 79451O-- January 23, 2011 ...[Visit Journal]
One of the great advantages of Type-II InAs/GaSb superlattice over other competing technologies for the third generation infrared imagers is the potential to have excellent uniformity across a large area as the electronic structure of the material is controlled by the layer thicknesses, not by the composition of the materials. This can economize the material growth, reduce the fabrication cost, and especially allow the realization of large format imagers. In this talk, we report the molecular beam epitaxial growth of Type-II superlattices on a 3-inch GaSb substrate for long wavelength infrared detection. The material exhibits excellent structural, optical and electrical uniformity via AFM, Xray, quantum efficiency and I-V measurements. At 77K, 11μm cutoff photodiodes exhibit more than 45% quantum efficiency, and a dark current density of 1.0x10-4 A/cm² at 50 mV, resulting in a specific detectivity of 6 x 1011 cm·Hz1/2/W. [reprint (PDF)]
 
1.  Thermal stability of GaN thin films grown on (0001) Al2O3, (0112) Al2O3 and (0001)Si 6H-SiC substrates
C.J. Sun, P. Kung, A. Saxler, H. Ohsato, E. Bigan, M. Razeghi, and D.K. Gaskill
Journal of Applied Physics 76 (1)-- July 1, 1994 ...[Visit Journal]
Single crystals of GaN were grown on (0001), (0112) Al2O3 and (0001)Si 6H‐SiC substrates using an atmospheric pressure metalorganic chemical‐vapor‐deposition reactor. The relationship has been studied between the thermal stability of the GaN films and the substrate’s surface polarity. It appeared that the N‐terminated (0001) GaN surface grown on (0001)Si 6H‐SiC has the most stable surface, followed by the nonpolar (1120) GaN surface grown on (0112) Al2O3, while the Ga‐terminated (0001) GaN surface grown on (0001) Al2O3 has the least stable surface. This is explained with the difference in the atomic configuration of each of these surfaces which induces a difference in their thermal decomposition. [reprint (PDF)]
 
1.  Monolithic terahertz source
Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi
Nature Photonics | Research Highlights -- July 31, 2014 ...[Visit Journal]
To date, the production of continuous-wave terahertz (THz) sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers operating at room temperature has proved elusive. A critical problem is that, to achieve a large nonlinear susceptibility for frequency conversion, the active region of the quantum cascade laser requires high doping, which elevates the lasing threshold current density. Now, Quan-Yong Lu and colleagues from Northwestern University in the USA have overcome this problem and demonstrated a room-temperature continuous-wave THz source based on difference-frequency generation in quantum cascade lasers. They designed quantum-well structures based on In0.53Ga0.47As/In0.52Al0.48As material system for two mid-infrared wavelengths. The average doping in the active region was about 2.5 × 1016 cm−3. A buried ridge, buried composite distributed-feedback waveguide with the Čerenkov phase-matching scheme was used to reduce the waveguide loss and enhance heat dissipation. As a result, single-mode emission at 3.6 THz was observed at 293 K. The continuous-wave THz power reached 3 μW with a conversion efficiency of 0.44 mW W−2 from mid-infrared to THz waves. Using a similar device design, a THz peak power of 1.4 mW was achieved in pulse mode. [reprint (PDF)]
 
1.  GaN avalanche photodiodes grown on m-plane freestanding GaN substrate
Z. Vashaei, E. Cicek, C. Bayram, R. McClintock and M. Razeghi
Applied Physics Letters, Vol. 96, No. 20, p. 201908-1-- May 17, 2010 ...[Visit Journal]
M-plane GaN avalanche p-i-n photodiodes on low dislocation density freestanding m-plane GaN substrates were realized using metal-organic chemical vapor deposition. High quality homoepitaxial m-plane GaN layers were developed; the root-mean-square surface roughness was less than 1 Å and the full-width-at-half-maximum value of the x-ray rocking curve for (1010) diffraction of m-plane GaN epilayer was 32 arcsec. High quality material led to a low reverse-bias dark current of 8.11 pA for 225 μm² mesa photodetectors prior to avalanche breakdown, with the maximum multiplication gain reaching about 8000. [reprint (PDF)]
 
1.  Dispersion compensated mid-infrared quantum cascade laser frequency comb with high power output
Q. Y. Lu, S. Manna, S. Slivken, D. H. Wu, and M. Razeghi
AIP Publishing -- April 26, 2017 ...[Visit Journal]
Chromatic dispersion control plays an underlying role in optoelectronics and spectroscopy owing to its enhancement to nonlinear interactions by reducing the phase mismatching. This is particularly important to optical frequency combs based on quantum cascade lasers which require negligible dispersions for efficient mode locking of the dispersed modes into equally spaced comb modes. Here, we demonstrated a dispersion compensated mid-IR quantum cascade laser frequency comb with high power output at room temperature. A low-loss dispersive mirror has been engineered to compensate the device’s dispersion residue for frequency comb generation. Narrow intermode beating linewidths of 40 Hz in the comb-working currents were identified with a high power output of 460 mW and a broad spectral coverage of 80 cm-1. This dispersion compensation technique will enable fast spectroscopy and high-resolution metrology based on QCL combs with controlled dispersion and suppressed noise. [reprint (PDF)]
 
1.  Growth and Characterization of Long-Wavelength Infrared Type-II Superlattice Photodiodes on a 3-in GaSb Wafer
B.M. Nguyen, G. Chen, M.A. Hoang, and M. Razeghi
IEEE Journal of Quantum Electronics (JQE), Vol. 47, No. 5, May 2011, p. 686-690-- May 11, 2011 ...[Visit Journal]
We report the molecular beam epitaxial growth and characterization of high performance Type-II superlattice photodiodes on 3” GaSb substrates for long wavelength infrared detection. A 7.3 micron thick device structure shows excellent structural homogeneity via atomic force microscopy and x-ray diffraction characterization. Optical and electrical measurements of photodiodes reveal not only the uniformity of the Type-II superlattice material but also of the fabrication process. Across the wafer, at 77 K, photodiodes with a 50% cut-off wavelength of 11 micron exhibit more than 45% quantum efficiency, and a dark current density of 1.0 x 10-4 A/cm² at 50 mV, resulting in a specific detectivity of 6x1011 cm·Hz1/2/W. [reprint (PDF)]
 
1.  Low frequency noise in 1024 x 1024 long wavelength infrared focal plane array base on Type-II InAs/GaSb superlattice
A. Haddadi, S.R. Darvish, G. Chen, A.M. Hoang, B.M. Nguyen and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 82680X-- January 22, 2012 ...[Visit Journal]
Recently, the type-II InAs/GaSb superlattice (T2SL) material platform is considered as a potential alternative for HgCdTe technology in long wavelength infrared (LWIR) imaging. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. In this paper, we report electrical low frequency noise measurement on a high performance type-II InAs/GaSb superlattice 1024×1024 LWIR focal plane array. [reprint (PDF)]
 
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)]
 

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