Page 18 of 23:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18  19 20 21 22 23  >> Next  (575 Items)

1.  Very High Average Power at Room Temperature from λ ~ 5.9 μm Quantum Cascade Lasers
J.S. Yu, S. Slivken, A. Evans, J. David and M. Razeghi
Virtual Journal of Nanoscale Science & Technology 26-- May 26, 2003 ...[Visit Journal][reprint (PDF)]
 
1.  Optoelectronic Integrated Circuits (OEICs) for Next Generation WDM Communications
M. Razeghi and S. Slivken
SPIE Conference, Boston, MA, -- July 29, 2002 ...[Visit Journal]
This paper reviews some of the key enabling technologies for present and future optoelectronic intergrated circuits. This review concentrates mainly on technology for lasers, waveguides, modulators, and fast photodetectors as the basis for next generation communicatiosn systems. Emphasis is placed on intergrations of components and mass production of a generic intelligent tranciever. [reprint (PDF)]
 
1.  High Performance Type-II InAs/GaSb Superlattice Photodiodes
H. Mohseni, Y. Wei, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 22, 2001 ...[Visit Journal]
We report on the demonstration of high performance p-i-n photodiodes based on Type-II InAs/GaSb superlattices operating in the very long wavelength infrared (VLWIR) range at 80 K. Material is grown by molecular beam epitaxy on GaSb substrates with excellent crystal quality as evidenced by x-ray diffraction and atomic force microscopy. The processed devices with a 50% cutoff wavelength of λc equals 22 μm show a peak current responsivity about 5.5 A/W at 80 K. The use of binary layers in the superlattice has significantly enhanced the uniformity and reproducibility of the energy gap. The 90% to 10% cut-off energy width of these devices is on the order of 2 kT which is about four times smaller compared to the devices based on InAs/Ga1-xInxSb superlattices. Similar photovoltaic devices with cut-off wavelengths up to 25 μm have been measured at 80 K. Our experimental results shows excellent uniformity over a three inch wafer area, indicating the possibility of VLWIR focal plane arrays based on Type-II superlattices. [reprint (PDF)]
 
1.  Band-gap narrowing and potential fluctuation in Si-doped GaN
I.H. Lee, J.J. Lee, P. Kung, F.J. Sanchez, and M. Razeghi
Applied Physics Letters 74 (1)-- January 4, 1999 ...[Visit Journal]
We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities. [reprint (PDF)]
 
1.  Electrical Transport Properties of Highly Doped N-type GaN Epilayers
H.J. Lee, M.G. Cheong, E.K. Suh, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 28, 1998 ...[Visit Journal]
Temperature-dependent Hall-effects in MOCVD-grown Si-doped GaN epilayers were measured as a function of temperature in the range 10-800 K. The results were satisfactorily analyzed in terms of a two-band model including the (Gamma) and impurity bands at lower temperatures than room. The (Gamma) band electrons are dominant only high temperatures. The ionized impurity scattering is the most important in the (Gamma) band except at very high temperatures. [reprint (PDF)]
 
1.  Quantum Hall liquid-to-insulator transition in In1-xGaxAs/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 In1-xGaxAs/InP heterostructure. When the magnetic field is at the critical field Bc, ρxx=0.86h/e². Furthermore, the transport near Bc scales as |B- Bc|T 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 Bc, within which z=1.0±0.1 and ν=2.1±0.3 are obtained from our data. [reprint (PDF)]
 
1.  Room Temperature Operation of InTlSb Infrared Photodetectors on GaAs
J.D. Kim, E. Michel, S. Park, J. Xu, S. Javadpour and M. Razeghi
Applied Physics Letters 69 (3)-- August 15, 1996 ...[Visit Journal]
Long-wavelength InTlSb photodetectors operating at room temperature are reported. The photo- detectors were grown on (100) semi-insulating GaAs substrates by low-pressure metalorganic chemical vapor deposition. Photoresponse of InTlSb photodetectors is observed up to 11 µm at room temperature. The maximum responsivity of an In0.96Tl0.04Sb photodetector is about 6.64 V/W at 77 K, corresponding to a detectivity of about 7.64 × 108 cm·Hz½/W. The carrier lifetime in InTlSb photodetectors derived from the stationary photoconductivity is 10–50 ns at 77 K. [reprint (PDF)]
 
1.  Growth of AlxGa1-xN:Ge on sapphire and silicon substrates
X. Zhang, P. Kung, A. Saxler, D. Walker, T.C. Wang, and M. Razeghi
Applied Physics Letters 67 (12)-- September 18, 1995 ...[Visit Journal]
AlxGa1–xN were grown on (00.1) sapphire and (111) silicon substrates in the whole composition range (0 <= x <= 1). The high optical quality of the epilayers was assessed by room-temperature optical absorption and photoluminescence measurements. Layers with higher Al composition are more resistive. Resistive AlxGa1–xN epilayers were successfully doped with Ge and free-electron concentration as high as 3 × 1019 cm–3 was achieved. [reprint (PDF)]
 
1.  Molecular Beam Epitaxial Growth of High Quality InSb for p-i-n Photodetectors
G. Singh, E. Michel, C. Jelen, S. Slivken, J. Xu, P. Bove, I. Ferguson, and M. Razeghi
Journal of Vacuum Science and Technology B, 13 (2)-- March 1, 1995 ...[Visit Journal]
The InSb infrared photodetectors grown heteroepitaxially on Si substrates by molecular beam epitaxy (MBE) are reported. Excellent InSb material quality is obtained on 3-inch Si substrates (with a GaAs predeposition) as confirmed by structural, optical, and electrical analysis. InSb infrared photodetectors on Si substrates that can operate from 77 K to room temperature have been demonstrated. The peak voltage-responsitivity at 4 μm is about 1.0×103 V/W and the corresponding Johnson-noise-limited detectivity is calculated to be 2.8×1010 cm·Hz½/W. This is the first important stage in developing InSb detector arrays or monolithic focal plane arrays (FPAs) on silicon. The development of this technology could provide a challenge to traditional hybrid FPA's in the future. [reprint (PDF)]
 
1.  Intermixing of GaInP/GaAs Multiple Quantum Wells
C. Francis, M.A. Bradley, P. Boucaud, F.H. Julien and M. Razeghi
Applied Physics Letters 62 (2)-- January 11, 1993 ...[Visit Journal]
The intermixing of GaInP‐GaAs superlattices induced by a heat treatment is investigated as a function of the annealing temperature and duration. Photoluminescence experiments reveal a large red shift of the effective band gap of the annealed quantum wells thus indicating a dominant self‐diffusion of the group III atoms which is confirmed by secondary ion mass spectroscopic measurements. For long enough annealing durations, the red shift saturates and even decreases due to the competing slower self‐diffusion of the group V atoms. Experiments are well understood based on a simple diffusion model. [reprint (PDF)]
 
1.  Surface plasmon enhanced light emission from AlGaN-based ultraviolet light-emitting diodes grown on Si (111)
Chu-Young Cho, Yinjun Zhang, Erdem Cicek, Benjamin Rahnema, Yanbo Bai, Ryan McClintock, and Manijeh Razeghi
Appl. Phys. Lett. 102, 211110 (2013)-- May 31, 2013 ...[Visit Journal]
We report on the development of surface plasmon (SP) enhanced AlGaN-based multiple quantum wells (MQWs) ultraviolet (UV) light-emitting diodes (LEDs) grown on silicon (111) substrates. In order to generate SP-coupling with the radiating dipoles in MQWs, an aluminum layer is selectively deposited in holes etched in the top p-AlGaN to p-GaN layers. After flip-chip bonding and substrate removal, an optical output power of ∼1.2 mW is achieved at an emission wavelength of 346 nm; the output power of these UV LEDs with Al layer is increased by 45% compared to that of conventional UV LEDs without Al layer. This enhancement can be attributed to an increase in the spontaneous emission rate and improved internal quantum efficiency via resonance coupling between excitons in MQWs and SPs in the aluminum layer. [reprint (PDF)]
 
1.  Superlattice sees colder objects in two colors and high resolution
M. Razeghi
SPIE Newsroom-- February 10, 2012 ...[Visit Journal]
A special class of semiconductor material can now detect two wavebands of light with energies less than a tenth of an electron volt in high resolution using the same IR camera. [reprint (PDF)]
 
1.  Amorphous ZnO films grown by room temperature pulsed laser deposition on paper and mylar for transparent electronics applications
D.J. Rogers, V.E. Sandana, F. Hosseini Teherani, R. McClintock, M. Razeghi, and H.J. Drouhin
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7940, p. 79401K-- January 24, 2011 ...[Visit Journal]
Recently, there has been a surge of activity in the development of next-generation transparent thin film transistors for use in applications such as electronic paper and flexible organic light emitting diode panels. Amongst the transparent conducting oxides attracting the most interest at present are Amorphous Oxide Semiconductors (AOS) based on ZnO because they exhibit enhanced electron mobility (μ), superior capacity for processability in air and improved thermodynamic stability compared with conventional covalent amorphous semiconductors and existing AOS. Moreover, they give excellent performance when fabricated at relatively low temperature and can readily be made in large area format. Thus, they are projected to resolve the trade-off between processing temperature and device performance and thereby allow fabrication on inexpensive heatsensitive substrates. For the moment, however, an undesireable post-deposition annealing step at a temperature of about 200ºC is necessary in order to obtain suitable electrical and optical properties. This paper demonstrates the possibility of directly engineering amorphous ZnO with relatively high conductiviy at room temperature on paper and mylar substrates using pulsed laser deposition. [reprint (PDF)]
 
1.  Deep ultraviolet (254 nm) focal plane array
E. Cicek, Z. Vashaei, R. McClintock, and M. Razeghi
SPIE Proceedings, Conference on Infrared Sensors, Devices and Applications; and Single Photon Imaging II, Vol. 8155, p. 81551O-1-- August 21, 2011 ...[Visit Journal]
We report the synthesis, fabrication and testing of a 320 × 256 focal plane array (FPA) of back-illuminated, solarblind, p-i-n, AlxGa1-xN-based detectors, fully realized within our research laboratory. We implemented a novel pulsed atomic layer deposition technique for the metalorganic chemical vapor deposition (MOCVD) growth of crackfree, thick, and high Al composition AlxGa1-xN layers. Following the growth, the wafer was processed into a 320 × 256 array of 25 μm × 25 μm pixels on a 30 μm pixel-pitch and surrounding mini-arrays. A diagnostic mini-array was hybridized to a silicon fan-out chip to allow the study of electrical and optical characteristics of discrete pixels of the FPA. At a reverse bias of 1 V, an average photodetector exhibited a low dark current density of 1.12×10-8 A·cm-2. Solar-blind operation is observed throughout the array with peak detection occurring at wavelengths of 256 nm and lower and falling off three orders of magnitude by 285 nm. After indium bump deposition and dicing, the FPA is hybridized to a matching ISC 9809 readout integrated circuit (ROIC). By developing a novel masking technology, we significantly reduced the visible response of the ROIC and thus the need for external filtering to achieve solar- and visible-blind operation is eliminated. This allowed the FPA to achieve high external quantum efficiency (EQE): at 254 nm, average pixels showed unbiased peak responsivity of 75 mA/W, which corresponds to an EQE of ~37%. Finally, the uniformity of the FPA and imaging properties are investigated. [reprint (PDF)]
 
1.  Noise analysis in Type-II InAs/GaSb Focal Plane Arrays
P.Y. Delaunay and M. Razeghi
Virtual Journal of Nanoscale Science and Technology, Vol. 20, No. 14-- October 5, 2009 ...[Visit Journal][reprint (PDF)]
 
1.  Techniques for High-Quality SiO2 Films
J. Nguyen and M. Razeghi
SPIE Conference, January 25-29, 2007, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices IV, Vol. 6479, p. 64791K-1-8-- January 29, 2007 ...[Visit Journal]
We report on the comparison of optical, structural, and electrical properties of SiO2 using plasma-enhanced chemical vapor deposition and ion-beam sputtering deposition. High-quality, low-temperature deposition of SiO2 by ion-beam sputtering deposition is shown to have lower absorption, smoother and more densely packed films, a lower amount of fixed oxide charges, and a lower trapped-interface density than SiO2 by plasma-enhanced chemical vapor deposition. This high-quality SiO2 is then demonstrated as an excellent electrical and mechanical surface passivation layer on Type-II InAs/GaSb photodetectors [reprint (PDF)]
 
1.  High-power, continuous-operation intersubband laser for wavelengths greater than 10 micron
S. Slivken, A. Evans, W. Zhang and M. Razeghi
Applied Physics Letters, Vol. 90, No. 15, p. 151115-1-- April 9, 2007 ...[Visit Journal]
In this letter, high-power continuous-wave emission (>100 mW) and high temperature operation (358 K) at a wavelength of 10.6 µm is demonstrated using an individual diode laser. This wavelength is advantageous for many medium-power applications previously reserved for the carbon dioxide laser. Improved performance was accomplished using industry-standard InP-based materials and by careful attention to design, growth, and fabrication limitations specific to long-wave infrared semiconductor lasers. The main problem areas are explored with regard to laser performance, and general steps are outlined to minimize their impact. [reprint (PDF)]
 
1.  Beam Steering in High-Power CW Quantum Cascade Lasers
W.W. Bewley, J.R. Lindle, C.S. Kim, I. Vurgaftman, J.R. Meyer, A.J. Evans, J.S. Yu, S. Slivken, and M. Razeghi
IEEE Journal of Quantum Electronics, 41 (6)-- June 1, 2005 ...[Visit Journal]
We report the light-current (L-I), spectral, and far-field characteristics of quantum cascade lasers (QCLs) with seven different wavelengths in the λ=4.3 to 6.3 μm range. In continuous-wave (CW) mode, the narrow-stripe (≈13 μm) epitaxial- side-up devices operated at temperatures up to 340 K, while at 295 K the CW output power was as high as 640 mW with a wallplug efficiency of 4.5%. All devices with λ≥4.7 μm achieved room-temperature CW operation, and at T=200 K several produced powers exceeding 1 W with ≈10% wallplug efficiency. The data indicated both spectral and spatial instabilities of the optical modes. For example, minor variations of the current often produced nonmonotonic hopping between spectra with envelopes as narrow as 5-10 nm or as broad as 200-250 nm. Bistable beam steering, by far-field angles of up to ±12° from the facet normal, also occurred, although even in extreme cases the beam quality never became worse than twice the diffraction limit. The observed steering is consistent with a theory for interference and beating between the two lowest order lateral modes. We also describe simulations of a wide-stripe photonic-crystal distributed-feedback QCL, which based on the current material quality is projected to emit multiple watts of CW power into a single-mode beam at T=200 K. [reprint (PDF)]
 
1.  Monolithic Integration of GaInAs/InP Quantum Well Infrared Photodetectors on Si Substrate
M. Erdtmann and M. Razeghi
SPIE Conference, San Jose, CA, -- January 22, 2001 ...[Visit Journal]
Using low-pressure metalorganic chemical vapor deposition, we have grown GaInAs/InP QWIP structures on GaAs-coated Si substrate. First, the procedure to optimize the epitaxy of the InP buffer layer on Si substrate is given. Excellent crystallinity and a mirror-like surface morphology were obtained by using both a two-step growth process at the beginning of the InP buffer layer growth and several series of thermal cycle annealing throughout the InP buffer layer growth. Second, results of fabricated GaInAs/InP QWIPs on Si substrate are presented. At a temperature of 80 K, the peak response wavelength occurs at 7.4 μm. The responsivities of QWIPs on both Si and InP substrates with identical structures are equal up to biases of 1.5 V. At a bias of 3 V, the responsivity of the QWIPs on Si substrate is 1.0 A/W. [reprint (PDF)]
 
1.  Uncooled InAs/GaSb Type-II infrared detectors grown on GaAs substrate for the 8–12 μm atmospheric window
H. Mohseni, J. Wojkowski, M. Razeghi, G. Brown, and W. Mitchel
IEEE Journal of Quantum Electronics 35 (7)-- July 1, 1999 ...[Visit Journal]
The operation of uncooled InAs-GaSb superlattice photodiodes with a cutoff wavelength of λc=8 μm and a peak detectivity of 1.2×108 cm·Hz½/W at zero bias is demonstrated. The detectivity is similar to the best uncooled HgCdTe detectors and microbolometers. However, the R0A product is more than two orders of magnitude higher than HgCdTe and the device is more than four orders of magnitude faster than microbolometers. These features combined with their low 1/f noise and high uniformity make these type-II photodiodes an excellent choice for uncooled high-speed IR imaging arrays [reprint (PDF)]
 
1.  High power asymmetrical InAsSb/InAsSbP/AlAsSb double heterostructure lasers emitting at 3.4 μm
D. Wu, B. Lane, H. Mohseni, J. Diaz and M. Razeghi
Applied Physics Letters 74 (9)-- March 1, 1999 ...[Visit Journal]
Midinfrared lasers with an asymmetrical InPAsSb/InAsSb/AlAsSb double heterostructure are reported. Using the asymmetrical double heterostructure, p- and n-cladding layers are separately optimized; high energy-gap AlAsSb (Eg ≈ 1.5 eV) for the p-type cladding layer to reduce the leakage current, and thus to increase To, and low energy-gap InPAsSb (Eg ≈ 0.5 eV) for the n-cladding layer to have low turn-on voltage. 100-μm-width broad-area lasers with 1000 μm cavity length exhibited peak output powers of 1.88 W in pulse and 350 mW in continuous wave modes per two facets at T=80 K with To of 54 K and turn-on voltage of 0.36 V. Maximum peak output powers up to 6.7 W were obtained from a laser bar of total aperture of 400 μm width and cavity length of 1000 μm, with a differential efficiency of 34% and far-field beam divergence narrower than 40° at 80 K. [reprint (PDF)]
 
1.  GaInN/GaN Multi-Quantum Well Laser Diodes Grown by Low-Pressure Metalorganic Chemical Vapor Deposition
P. Kung, A. Saxler, D. Walker, A. Rybaltowski, X. Zhang, J. Diaz, and M. Razeghi
MRS Internet Journal of Nitride Semiconductor Research 3 (1)-- January 1, 1998 ...[Visit Journal]
We report the growth, fabrication and characterization of GaInN/GaN multi-quantum well lasers grown on (00·1) sapphire substrates by low pressure metalorganic chemical vapor deposition. The threshold current density of a 1800 µm long cavity length laser was 1.4 kA/cm² with a threshold voltage of 25 V. These lasers exhibited series resistances of 13 and 14 Ω at 300 and 79 K, respectively. [reprint (PDF)]
 
1.  AlxGa1-xN (0 ≤ x ≤ 1) Ultraviolet Photodetectors Grown on Sapphire by Metal-organic Chemical-vapor Deposition
D. Walker, X. Zhang, A. Saxler, P. Kung, J. Xu, and M. Razeghi
Applied Physics Letters 70 (8)-- February 24, 1997 ...[Visit Journal]
AlxGa1–xN (0 ≤ x ≤ 1) ultraviolet photoconductors with cutoff wavelengths from 365 to 200 nm have been fabricated and characterized. The maximum detectivity reached 5.5 × 108 cm·Hz1/2/W at a modulating frequency of 14 Hz. The effective majority carrier lifetime in AlxGa1–xN materials, derived from frequency-dependent photoconductivity measurements, has been estimated to be from 6 to 35 ms. The frequency-dependent noise spectrum shows that it is dominated by Johnson noise at high frequencies for low-Al-composition samples. [reprint (PDF)]
 
1.  Photovoltaic effects in GaN structures with p-n junction
X. Zhang, P. Kung, D. Walker, J. Piotrowski, A. Rogalski, A. Saxler, and M. Razeghi
Applied Physics Letters 67 (14)-- October 2, 1995 ...[Visit Journal]
Large-area GaN photovoltaic structures with p-n junctions have been fabricated using atmospheric pressure metalorganic chemical vapor deposition. The photovoltaic devices typically exhibit selective spectral characteristics with two narrow peaks of opposite polarity. This can be related to p-n junction connected back‐to‐back with a Schottky barrier. The shape of the spectral characteristic is dependent on the thickness of the n- and p-type regions. The diffusion length of holes in the n-type GaN region, estimated by theoretical modeling of the spectral response shape, was about 0.1 μm. [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)]
 

Page 18 of 23:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18  19 20 21 22 23  >> Next  (575 Items)