Publications by    
Page 21 of 27:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21  22 23 24 25 26 27  >> Next  (673 Items)

501.  Continuous-wave room-temperature operation of InGaN/GaN multiquantum well lasers grown by low-pressure metalorganic chemical vapor deposition
M. Razeghi, A. Saxler, P. Kung, D. Walker, X. Zhang, A. Rybaltowski, Y. Xiao, H.J. Yi and J. Diaz
SPIE Conference, San Jose, CA, Vol. 3284, pp. 113-- January 28, 1998
Continuous-wave (CW) room temperature operation of InGaN/GaN multi-quantum well (MQW) lasers is reported. Far-field beam divergence as narrow as 13 degrees and 20 degrees for parallel and perpendicular directions to epilayer planes were measured, respectively. The MQW lasers showed strong beam polarization anisotropy as consistent with QW laser gain theory. Dependencies of threshold current on cavity-length and temperature are also consistent with conventional laser theory. No significant degradation in laser characteristics was observed during lifetime testing for over 140 hours of CW room temperature operation. reprint
502.  Narrow gap semiconductor photodiodes
A. Rogaski and M. Razeghi
-- January 28, 1998
503.  GaN p-i-n photodiodes with high visible-to-ultraviolet rejection ratio
P. Kung, X. Zhang, D. Walker, A. Saxler, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 28, 1998
UV photodetectors are critical components in many applications, including UV astronomy, flame sensors, early missile threat warning and space-to-space communications. Because of the presence of strong IR radiation in these situations, the photodetectors have to be solar blind, i.e. able to detect UV radiation while not being sensitive to IR. AlxGa1-xN is a promising material system for such devices. AlxGa1-xN materials are wide bandgap semiconductors, with a direct bandgap whose corresponding wavelength can be continuously tuned from 200 to 365 nm. AlxGa1-xN materials are thus insensitive to visible and IR radiation whose wavelengths are higher than 365 nm. We have already reported the fabrication and characterization of AlxGa1-xN-based photoconductors with a cut-off wavelength tunable from 200 to 365 nm by adjusting the ternary alloy composition. Here, we present the growth and characterization of GaN p-i- n photodiodes which exhibit a visible-to-UV rejection ratio of 6 orders or magnitude. The thin films were grown by low pressure metalorganic chemical vapor deposition. Square mesa structures were fabricated using dry etching, followed by contact metallization. The spectral response, rejection ratio and transient response of these photodiodes is reported. reprint
504.  Responsivity and Noise Performance of InGaAs/InP Quantum Well Infrared Photodetectors
C. Jelen, S. Slivken, T. David, G. Brown, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 28, 1998
Dark current nose measurements were carried out between 10 and 104 Hz at T = 80K on two InGaAs/InP quantum well IR photo detectors (QWIPs) designed for 8 μm IR detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependent gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate is similar to AlGaAs/GaAs QWIPs with similar peak wavelengths, but the gain is 50X larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers. As a result, a large responsivity of 7.5 A/W at 5V bias and detectivity of 5 X 1011 cm·Hz½/W at 1.2 V bias were measured for the InGaAs/InP QWIPs at T = 80K. reprint
505.  Growth and characterization of InAs/GaSb Type-II superlattices for long-wavelength infrared detectors
H. Mohseni, E. Michel, M. Razeghi, W. Mitchel, and G. Brown
SPIE Conference, San Jose, CA, -- January 28, 1998
We report the molecular beam epitaxial growth and characterization of InAs/GaSb superlattices grown on semi- insulating GaAs substrate for long wavelength IR detectors. Photoconductive detectors fabricated from the superlattices showed 80% cut-off at 11.6 μm and peak responsivity of 6.5 V/W with Johnson noise limited detectivity of 2.36 x 109 cm·Hz½/W at 10.7 μm at 78 K. The responsivity decreases at higher temperatures with a T-2 behavior rather than exponential decay, and at room temperature the responsivity is about 660 mV/W at 11 μm. Lower Auger recombination rate in this system provides comparable detectivity to the best HgCdTe detectors at 300K. Higher uniformity over large areas, simpler growth and the possibility of having read-out circuits in the same GaAs chip are the advantages of this system over HgCdTe detectors for near room temperature operation. reprint
506.  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
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
507.  New Developments in III-Nitride Material and Device Applications
M. Razeghi, A. Saxler, P. Kung, D. Walker, X. Zhang, K.S. Kim, H.R. Vydyanath, J. Solomon, M. Ahoujja, and W.C. Mitchel
-- January 1, 1998
508.  Infrared Photodetectors and Imaging Arrays Using Advanced III-V Materials
M. Razeghi
-- January 1, 1998
509.  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
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
510.  Simultaneous growth of two differently oriented GaN epilayers on (11.0) sapphire (II) a growth model of (00.1) and (10.0) GaN
T. Kato, P. Kung, A. Saxler, C.J. Sun, H. Ohsato, M. Razeghi and T. Okuda
-- January 1, 1998
511.  Recent advances in Sb-based materials for uncooled infrared photodetectors
E. Michel and M. Razeghi
-- January 1, 1998
512.  Exploration of InSbBi for uncooled long-wavelength infrared photodetectors
J.J. Lee and M. Razeghi
-- January 1, 1998
513.  High-Power Al-free InGaAsP/GaAs Near-Infrared Semiconductor Lasers
M. Razeghi and H. Yi
-- January 1, 1998
514.  GaN-Based Laser Diodes
Manijeh Razeghi
International Journal of High Speed Electronics and Systems (IJHSES), Volume: 9, Issue: 4, pp. 1007-1080 (1998)-- January 1, 1998
We discuss optical properties of III-Nitride materials and structures. These properties are critical for the development of III-Nitride-based light-emitting diodes and laser diodes. Minority carrier diffusion length in GaN has been determined to be ~0.1 μm. The properties of lasing in GaN have been studied using optical pumping. The red shift of emission peak observed in stimulated emission of GaN has been modeled and attributed to many-body interactions at high excitation. The correlation of photoluminescence and optical pumping has shown that band-to-band, or shallow donor-related bandtail to valence band transition is the necessary mechanism of lasing in GaN. This work showed that the thermal instability of InGaN at growth temperature is of main concern in the fabrication of InGaN-based MQW laser diode structures. Photoluminescence has shown that the InGaN composition is very sensitive to the growth temperature. Therefore InGaN growth temperature should be strictly controlled during InGaN-based MQW growth. This work discovered that proper annealing of Si-doping of InGaN/GaN MQW structures that are properly annealed could reduce the lasing threshold and improve the slope efficiency. Over-annealing of these MQWs can lead to thermal degradation of the active layer. Si-doping in over-annealed MQW structure further degrades its quality. The degradation has been attributed to the increase of defects and/or nonuniform local potential formation. P-type doping on the top of InGaN/GaN could also lead to the formation of compensation layer which also degrades laser diode performances. Optical confinement and carrier confinement in InGaN-based laser diode structures are evaluated for optimum laser diode design. The state-of-the-art and fundamental issues of InGaN-based light-emitting diodes and laser diodes are discussed.
515.  InP-based Multi-Spectral Quantum Well Infrared Photodetectors
C. Jelen and M. Razeghi
-- December 11, 1997
516.  Mid-Infrared Quantum Cascade Lasers Grown by Gas-Source Molecular Beam Epitaxy
S. Slivken and M. Razeghi
-- December 11, 1997
517.  Comparison of Trimethylgallium and Triethylgallium for the Growth of GaN
A. Saxler, D. Walker, P. Kung, X. Zhang, M. Razeghi, J. Solomon, W. Mitchel, and H.R. Vydyanath
Applied Physics Letters 71 (22)-- December 1, 1997
GaN films grown by low-pressure metalorganic chemical vapor deposition using trimethylgallium and triethylgallium as gallium precursors are compared. The films were characterized by x-ray diffraction, Hall effect, photoluminescence, secondary ion mass spectroscopy, and etch pit density measurements. GaN layers grown using triethylgallium exhibited superior electrical and optical properties and a lower carbon impurity concentration. reprint
518.  Long-term reliability of Al-free InGaAsP/GaAs λ = 808 nm) lasers at high-power high-temperature operation
J. Diaz, H. Yi, M. Razeghi and G.T. Burnham
Applied Physics Letters 71 (21)-- November 24, 1997
We report the long-term reliability measurement on uncoated Al-free InGaAsP/GaAs (λ = 808 nm) lasers at high-power and high-temperature operation. No degradation in laser performance has been observed for over 30 ,000 h of lifetime testing in any of randomly selected several 100 μm-wide uncoated lasers operated at 60 °C with 1 W continuous wave output power. This is the first and the most conclusive evidence ever reported that directly shows the high long-term reliability of uncoated Al-free lasers. reprint
519.  Reliable High-Power Uncoated Al-free InGaAsP/GaAs Lasers for Cost-Sensitive Optical Communication and Processing Applications
M. Razeghi
SPIE Conference, Dallas, TX, -- November 4, 1997
Unlike InP-based systems for long-distance communication applications, GaAs-based optoelectronic systems mostly for local-area network, optical interconnection or optical computing are very cost-sensitive because often these optoelectronic devices constitute most of the cost for these applications and fewer users share the cost. Thus besides technical issues, the processing cost should be addressed in the selection of materials and fabrication methods. We discuss a number of major advantages of Al-free InGaAsP/GaAs lasers for these applications, such as not coating- requirement, low cost, high long-term reliability, high performance. We discuss recent preliminary results of Al- free lasers as a first step toward these optoelectronic applications. reprint
520.  Gas-Source Molecular Beam Epitaxy Growth of 8.5 μm Quantum Cascade Laser
S. Slivken, C. Jelen, A. Rybaltowski, J. Diaz and M. Razeghi
Applied Physics Letters 71 (18)-- November 1, 1997
We demonstrate preliminary results for an 8.5 μm laser emission from quantum cascade lasers grown in a single step by gas-source molecular beam epitaxy. 70 mW peak power per two facets is recorded for all devices tested at 79 K with 1 μs pulses at 200 Hz. For a 3 mm cavity length, lasing persists up to 270 K with a T0 of 180 K. reprint
521.  High power InAsSb/InPAsSb/InAs mid-infrared lasers
A. Rybaltowski, Y. Xiao, D. Wu, B. Lane, H. Yi, H. Feng, J. Diaz, and M. Razeghi
Applied Physics Letters 71 (17)-- October 27, 1997
We demonstrate high-power InAsSb/InPAsSb laser bars (λ ≈ 3.2 μm) consisting of three 100 μm-wide laser stripes of 700 μm cavity length, with peak output power up to 3 W at 90 K, and far-fields for the direction perpendicular to the junction as narrow as 12° full width half maximum. Spectra and far-field patterns of the laser bars are shown to have excellent characteristics for a wide range of operating conditions, suggesting the possibility of even higher light power emission with good beam quality. Joule heating is shown to be the major factor limiting higher power operation. reprint
522.  Long-Wavelength Infrared Photodetectors Based on InSbBi Grown on GaAs Substrates
J.J. Lee, J.D. Kim, and M. Razeghi
Applied Physics Letters 71 (16)-- October 20, 1997
We demonstrate the operation of InSbBi infrared photoconductive detectors grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The fabricated photodetector showed a cutoff wavelength of 7.7 μm at 77 K. The responsivity of the InSbBi photodetector at 7 μm was about 3.2 V/W at 77 K. The corresponding Johnson-noise limited detectivity was 4.7×108  cm· Hz½/W. The carrier lifetime was estimated to be about 86 ns from the voltage-dependent responsivity measurements. reprint
523.  High-Quality Quantum Cascade Lasers Grown by GSMBE
S. Slivken, C. Jelen, J. Diaz, and M. Razeghi
-- October 1, 1997
524.  The Center for Quantum Devices - extending the scope of photonics
M. Razeghi
-- October 1, 1997
525.  Photoresponse of InGaAsP-based p-doped quantum well infrared photodetectors
M. Tadic, C. Jelen, S. Slivken, and M. Razeghi
-- September 14, 1997

Page 21 of 27:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21  22 23 24 25 26 27  >> Next  (673 Items)