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1.  Pulsed metal-organic chemical vapor deposition of high quality AlN/GaN superlattices for near-infrared intersubband transitions
C. Bayram, N. Pere-Laperne, R. McClintock, B. Fain and M. Razeghi
Applied Physics Letters, Vol. 94, No. 12, p. 121902-1-- March 23, 2009 ...[Visit Journal]
A pulsed metal-organic chemical vapor deposition technique is developed for the growth of high-quality AlN/GaN superlattices (SLs) with intersubband (ISB) transitions at optical communications wavelengths. Tunability of the AlN and GaN layers is demonstrated. Indium is shown to improve SL surface and structural quality. Capping thickness is shown to be crucial for ISB transition characteristics. Effects of barrier- and well-doping on the ISB absorption are reported. [reprint (PDF)]
 
1.  Sb-based infrared materials and photodetectors for the near room temperature applications
J.D. Kim, E. Michel, H. Mohseni, J. Wojkowski, J.J. Lee and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 2999, pp. 55-- February 12, 1997 ...[Visit Journal]
We report on the growth of InSb, InAsSb, and InTlSb alloys for infrared photodetector applications. The fabrication and characterization of photodetectors based on these materials are also reported. Both photoconductive and photovoltaic devices are investigated. The materials and detector structures were grown on (100) and (111)B semi-insulating GaAs and GaAs coated Si substrates by low pressure metalorganic chemical vapor deposition and solid source molecular beam epitaxy. Photoconductive detectors fabricated from InAsSb and InTlSb have been operated in the temperature range from 77 K to 300 K. The material parameters for photovoltaic device structures have been optimized through theoretical calculations based on fundamental mechanisms. InSb p-i-n photodiodes with 77 K peak responsivities approximately 103 V/W were grown on Si and (111) GaAs substrates. An InAsSb photovoltaic detector with a composition of x equals 0.85 showed photoresponse up to 13 micrometers at 300 K with a peak responsivity of 9.13 X 10-2 V/W at 8 micrometers . The RoA product of InAsSb detectors has been theoretically and experimentally analyzed. [reprint (PDF)]
 
1.  Polarization-free GaN emitters in the ultraviolet and visible spectra via heterointegration on CMOS-compatible Si (100)
C. Bayram, J. Ott, K. T. Shiu, C. W. Cheng, Y. Zhu, J. Kim, D. K. Sadana, M. Razeghi
Proc. SPIE 9370, Quantum Sensing and Nanophotonic Devices XII, 93702F (February 8, 2015); -- February 8, 2015 ...[Visit Journal]
This work presents a new type of polarization-free GaN emitter. The unique aspect of this work is that the ultraviolet and visible emission originates from the cubic phase GaN and the cubic phase InGaN/GaN multi-quantum-wells, respectively. Conventionally, GaN emitters (e.g. light emitting diodes, laser diodes) are wurtzite phase thus strong polarization fields exist across the structure contributing to the “droop” behavior – a phenomenon defined as “the reduction in emitter efficiency as injection current increases”. The elimination of piezoelectric fields in GaN-based emitters as proposed in this work provide the potential for achieving a 100% internal efficiency and might lead to droopfree light emitting diodes. In addition, this work demonstrates co-integration of GaN emitters on cheap and scalable CMOS-compatible Si (100) substrate, which yields possibility of realizing a GaN laser diode uniquely – via forming mirrors along the naturally occurring cubic phase GaN-Si(100) cleavage planes. [reprint (PDF)]
 
1.  Near milliwatt power AlGaN-based ultraviolet light emitting diodes based on lateral epitaxial overgrowth of AlN on Si(111)
Y. Zhang, S. Gautier, C. Cho, E. Cicek, Z, Vashaei, R. McClintock, C. Bayram, Y. Bai and M. Razeghi
Applied Physics Letters, Vol. 102, No. 1, p. 011106-1-- January 7, 2013 ...[Visit Journal]
We report on the growth, fabrication, and device characterization of AlGaN-based thin-film ultraviolet (UV) (λ ∼ 359 nm) light emitting diodes (LEDs). First, AlN/Si(111) template is patterned. Then, a fully coalesced 7-μm-thick lateral epitaxial overgrowth (LEO) of AlN layer is realized on patterned AlN/Si(111) template followed by UV LED epi-regrowth. Metalorganic chemical vapor deposition is employed to optimize LEO AlN and UV LED epitaxy. Back-emission UV LEDs are fabricated and flip-chip bonded to AlN heat sinks followed by Si(111) substrate removal. A peak pulsed power and slope efficiency of ∼0.6 mW and ∼1.3 μW/mA are demonstrated from these thin-film UV LEDs, respectively. For comparison, top-emission UV LEDs are fabricated and back-emission LEDs are shown to extract 50% more light than top-emission ones. [reprint (PDF)]
 
1.  High-Power Continuous-Wave Operation of a 6 µm Quantum-Cascade Laser at Room Temperature
J.S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi
Applied Physics Letters, 83 (13)-- September 29, 2003 ...[Visit Journal]
We report continuous-wave (cw) operation of quantum-cascade lasers (λ= 6 µm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 308 K (35 °C). The high cw optical output powers of 132 mW at 293 K and 21 mW at 308 K are achieved with threshold current densities of 2.29 and 2.91 kA/cm², respectively, for a high-reflectivity-coated 15 µm wide and 2 mm long laser. [reprint (PDF)]
 
1.  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 ...[Visit Journal]
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 (PDF)]
 
1.  Defects in Organometallic Vapor-Phase Epitaxy-Grown GaInP Layers
Feng S.L., Bourgoin J.C., Omnes F., and Razeghi M.
Applied Physics Letters 59 (8), p. 941-- May 28, 1991 ...[Visit Journal]
Non-intentionally doped metalorganic vapor‐phase epitaxy Ga1−x InxP layers, having an alloy composition (x = 0.49) corresponding to a lattice matched to GaAs, grown by metalorganic chemical vapor deposition, have been studied by capacitance‐voltage and deep-level transient spectroscopy techniques. They are found to exhibit a free‐carrier concentration at room temperature of the order of 1015 cm−3. Two electron traps have been detected. The first one, at 75 meV below the conduction band, is in small concentration (∼1013 cm−3) while the other, at about 0.9 eV and emitting electrons above room temperature, has a concentration in the range 1014–1015 cm−3. [reprint (PDF)]
 
1.  High-detectivity quantum-dot infrared photodetectors grown by metal-organic chemical-vapor deposition
J. Szafraniec, S. Tsao, W. Zhang, H. Lim, M. Taguchi, A.A. Quivy, B. Movaghar and M. Razeghi
Applied Physics Letters 88 (121102)-- March 20, 2006 ...[Visit Journal]
A mid-wavelength infrared photodetector based on InGaAs quantum dots buried in an InGaP matrix and deposited on a GaAs substrate was demonstrated. Its photoresponse at T=77 K was measured to be around 4.7 μm with a cutoff at 5.5 μm. Due to the high peak responsivity of 1.2 A/W and low dark-current noise of the device, a specific peak detectivity of 1.1 x 1012 cm·Hz½·W−1 was achieved at −0.9 V bias [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.  Optical Coatings by ion-beam sputtering deposition for long-wave infrared quantum cascade lasers
J. Nguyen, J.S. Yu, A. Evans, S. Slivken and M. Razeghi
Applied Physics Letters, 89 (11)-- September 11, 2006 ...[Visit Journal]
The authors report on the development of high-reflection and multilayer antireflection coatings using ion-beam sputtering deposition for long-wave infrared (λ~9.4 μm) quantum cascade lasers. A metallic high-reflection coating structure using Y2O3 and Au is demonstrated to achieve a high reflectance of 96.70%, and the use of a multilayer anti-reflection coating structure using PbTe and ZnO is demonstrated to achieve a very low reflectance of 1.64%. [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.  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.  Generalized k·p perturbation theory for atomic-scale superlattices
H. Yi and M. Razeghi
Physical Review B 56 (7)-- August 15, 1997 ...[Visit Journal]
We present a generalized k⋅p perturbation method that is applicable for atomic-scale superlattices. The present model is in good quantitative agreement with full band theories with local-density approximation, and approaches results of the conventional k⋅p perturbation method (i.e., Kane’s Hamiltonian) with the envelope function approximation for superlattices with large periods. The indirect band gap of AlAs/GaAs superlattices with short periods observed in experiments is explained using this method. [reprint (PDF)]
 
1.  Optical Investigations of GaAs-GaInP Quantum Wells and Superlattices Grown by Metalorganic Chemical Vapor Deposition
Omnes F., and Razeghi M.
Applied Physics Letters 59 (9), p. 1034-- May 28, 1991 ...[Visit Journal]
Recent experimental results on the photoluminescence and photoluminescence excitation of GaAs‐Ga0.51In0.49P lattice‐matched quantum wells and superlattices are discussed. The full width at half maximum of a 10‐period GaAs‐GaInP superlattice with Lz=90 Å and LB=100 Å is 4 meV at 4 K. The photoluminescence excitation exhibits very sharp peaks attributed to the electron to light‐hole and electron to heavy‐hole transitions. The GaInP‐GaAs interface suffers from memory effect of In, rather than P or As elements. [reprint (PDF)]
 
1.  World's first demonstration of type-II superlattice dual band 640 x 512 LWIR focal plane array
E.K. Huang and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 82680Z-- January 22, 2012 ...[Visit Journal]
High resolution multi-band infrared detection of terrestrial objects is useful in applications such as long range and high altitude surveillance. In this paper, we present a 640 x 512 type-II superlattice focal plane array (FPA) in the long-wave infrared (LWIR) suitable for such purposes, featuring 100% cutoff wavelengths at 9.5 μm (blue channel) and 13 μm (red). The dual band camera is single-bump hybridized to an Indigo 30 μm pitch ISC0905 read-out integrated circuit. Test pixels revealed background limited behavior with specific detectivities as high as ~5x1011 Jones at 7.9 μm (blue) and ~1x1011 Jones at 10.2 μm (red) at 77K. [reprint (PDF)]
 
1.  Electrically pumped photonic crystal distributed feedback quantum cascade lasers
Y. Bai, S.R. Darvish, S. Slivken, P. Sung, J. Nguyen, A. Evans, W. Zhang, and M. Razeghi
Applied Physics Letters, Vol. 91, No. 14, p. 141123-1-- October 1, 2007 ...[Visit Journal]
We demonstrate electrically pumped, room temperature, single mode operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting at ~4.75 µm. Ridge waveguides of 100 µm width were fabricated with both PCDFB and Fabry-Pérot feedback mechanisms. The Fabry-Pérot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half maximum of 2.4°. This accomplishment represents the first step in power scaling of single mode, midinfrared laser diodes operating at room temperature. [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.  Long Wavelength Type-II Photodiodes Operating at Room Temperature
H. Mohseni and M. Razeghi
IEEE Photonics Technology Letters 13 (5)-- May 1, 2001 ...[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.  Engineering future light emitting diodes and photovoltaics with inexpensive materials: Integrating ZnO and Si into GaN-based devices
C. Bayram ; K. T. Shiu ; Y. Zhu ; C. W. Cheng ; D. K. Sadana ; F. H. Teherani ; D. J. Rogers ; V. E. Sandana ; P. Bove ; Y. Zhang ; S. Gautier ; C.-Y. Cho ; E. Cicek ; Z. Vashaei ; R. McClintock ; M. Razeghi
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 86260L (March 18, 2013)-- March 18, 2013 ...[Visit Journal]
Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our results suggest that groove structures are very promising for controlled local epitaxy of cubic phase GaN. Overall, it is concluded that there are significant opportunities for cost reduction in novel hybrid diodes based on ZnO-InGaN-Si hybridization. [reprint (PDF)]
 
1.  InGaAs/InGaP Quantum-Dot Photodetector with a High Detectivity
H. Lim, S. Tsao, M. Taguchi, W. Zhang, A. Quivy and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270N-- January 23, 2006 ...[Visit Journal]
Quantum-dot infrared photodetectors (QDIPs) have recently been considered as strong candidates for numerous applications such as night vision, space communication, gas analysis and medical diagnosis involving middle and long wavelength infrared (MWIR and LWIR respectively) operation. This is due to their unique properties arising from their 3-dimensional confinement potential that provides a discrete density of states. They are expected to outperform quantum-well infrared photodetectors (QWIPs) as a consequence of their natural sensitivity to normal incident radiation, their higher responsivity and their higher-temperature operation. So far, most of the QDIPs reported in the literature were based on the InAs/GaAs system and were grown by molecular beam epitaxy (MBE). Here, we report on the growth of a high detectivity InGaAs/InGaP QDIP grown on a GaAs substrate using low-pressure metalorganic chemical vapor deposition (MOCVD). [reprint (PDF)]
 
1.  Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency
A. Evans, S.R. Darvish, S. Slivken, J. Nguyen, Y. Bai and M. Razeghi
Applied Physics Letters, Vol. 91, No. 7, p. 071101-1-- August 13, 2007 ...[Visit Journal]
The authors report on the development of ~4.7 µm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675 W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150 K, with continuous-wave output powers of more than 1 W. [reprint (PDF)]
 
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
Applied Physics Letters, 82 (20)-- May 19, 2003 ...[Visit Journal]
We report a very high average output power at room temperature for quantum-cascade lasers emitting at λ ~ 5.9 µm. For high-reflectivity-coated 2-mm-long cavities, a low threshold current density of 1.7 kA/cm2 was obtained at room temperature. From 300 to 400 K, the characteristic temperature (T0) was 198 K. A maximum average output power of 0.67 W was achieved. In addition, 0.56 W average output power was observed at a duty cycle of 56%. [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.  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.  Recent advances in III-Nitride materials, characterization and device applications
M. Razeghi, X. Zhang, P. Kung, A. Saxler, D. Walker, K.Y. Lim, and K.S. Kim
SPIE Conference: Solid State Crystals in Optoelectronics and Semiconductor Technology; Proceedings 3179-- October 7, 1996 ...[Visit Journal]
High-quality AlN, GaN, AlGaN have been grown on sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The x-ray rocking curve of AlN and GaN were 100 arcsecs and 30 arcsecs respectively with Pendelloesung oscillations, which are the best reported to date. GaN with high crystallinity simultaneously exhibited high optical and electrical quality. Photoluminescence linewidth of GaN at 77K was as low as 17 meV, which is the best reported to date. Si-doped GaN had a mobility higher than 300 cm²/V·s. GaN has been also successfully grown on LiGaO2 substrate with LP-MOCVD for the first time. AlGaN for the entire composition range has been grown. These layers exhibited the lowest x-ray FWHM reported to date. The excellent optical quality of these layers have been characterized by room temperature UV transmission and photoluminescence. N-type doping of AlGaN with Si has ben achieved up to 60 percent Al with mobility as high as 78 cm²/V·s. AlxGa1-xN/AlyGa1-yN superlattice with atomically sharp interface have been demonstrated. Optically-pumped stimulated emission in GaN:Ge and GaN:Si has been observed with threshold optical power density as low as 0.4 MW/cm². AlGaN photoconductors with cut-off wavelengths from 200 nm to 365 nm have been achieved for the first time. GaN p-n junction photovoltaic detector with very selective photoresponse have been demonstrated and theoretically modeled. Ti/AlN/Si metal-insulator- semiconductor capacitor with high capacitance-voltage performances at both low and high frequencies and low interface trap level density have been demonstrated for the first time in this material system. [reprint (PDF)]
 

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