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1.  Molecular Beam Epitaxial Growth of High Quality InSb
E. Michel, G. Singh, S. Slivken, C. Besikci, P. Bove, I. Ferguson, and M. Razeghi
Applied Physics Letters 65 (26)-- December 26, 1994 ...[Visit Journal]
In this letter we report on the growth of high quality InSb by molecular beam epitaxy that has been optimized using reflection high energy electron diffraction. A 4.8 µm InSb layer grown on GaAs at a growth temperature of 395 °C and a III/V incorporation ratio of 1:1.2 had an x-ray rocking curve of 158 arcsec and a Hall mobility of 92,300 cm²·V−1 at 77 K. This is the best material quality obtained for InSb nucleated directly onto GaAs reported to date. [reprint (PDF)]
 
1.  Reliable GaN-based resonant tunneling diodes with reproducible room-temperature negative differential resistance
C. Bayram, D.K. Sadana, Z. Vashaei and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 826827-- January 22, 2012 ...[Visit Journal]
negative differential resistance (NDR). Compared to other negative resistance devices such as (Esaki) tunnel and transferred-electron devices, RTDs operate much faster and at higher temperatures. III-nitride materials, composed of AlGaInN alloys, have wide bandgap, high carrier mobility and thermal stability; making them ideal for high power high frequency RTDs. Moreover, larger conduction band discontinuity promise higher NDR than other materials (such as GaAs) and room-temperature operation. However, earlier efforts on GaN-based RTD structures have failed to achieve a reliable and reproducible NDR. Recently, we have demonstrated for the first time that minimizing dislocation density and eliminating the piezoelectric fields enable reliable and reproducible NDR in GaN-based RTDs even at room temperature. Observation of NDR under both forward and reverse bias as well as at room and low temperatures attribute the NDR behaviour to quantum tunneling. This demonstration marks an important milestone in exploring III-nitride quantum devices, and will pave the way towards fundamental quantum transport studies as well as for high frequency optoelectronic devices such as terahertz emitters based on oscillators and cascading structures. [reprint (PDF)]
 
1.  Injector doping level dependent continuous-wave operation of InP-based QCLs at λ~ 7.3 µm above room temperature
J.S. Yu, S. Slivken, and M. Razeghi
Semiconductor Science and Technology (SST), Vol. 25, No. 12, p. 125015-- December 1, 2010 ...[Visit Journal]
We report the continuous-wave (CW) operation of InGaAs/InAlAs quantum cascade lasers (QCLs) operating at λ ~ 7.3 µm above room temperature. The injector doping level–dependent CW characteristics above room temperature are investigated for doping densities between 7 × 1016 cm−3 and 2 × 1017 cm−3. The device performance, i.e. threshold current density, output power, operating temperature and characteristic temperature, depends strongly on the injector doping density. For a relatively low injector doping density of 7 × 1016 cm−3, a high-reflectivity-coated 10 µm wide and 4 mm long laser exhibits an improved device performance with an output power of 152 mW and a threshold current density of 1.37 kA cm−2 at 298 K under CW mode, operating up to 343 K. The thermal characteristics are also analyzed by the estimation from the experimentally measured data for the QCLs with different injector doping densities. [reprint (PDF)]
 
1.  Hybrid green LEDs with n-type ZnO substituted for N-type GaN in an inverted P-N junction
F. Hosseini Teherani; M. Razeghi; D.J. Rogers; Can Bayram; R. McClintock
LEOS Annual Meeting Conference Proceedings, LEOS '09. IEEE, [5343231] (2009) -- October 4, 2009 ...[Visit Journal]
Recently, the GaN and ZnO materials systems have attracted considerable attention because of their use in a broad range of emerging applications including light-emitting diodes (LEDs) and solar cells. GaN and ZnO are similar materials with direct wide bandgaps, wurtzite crystal structure, high thermal stability and comparable thermal expansion coefficients, which makes them well suited for heterojunction fabrication. Two important advantages of GaN over ZnO are the reliable p-type doping and the mature know-how for bandgap engineering. Thus GaN-based LEDs can be made to emit from the deep UV right into the green through alloying with Al and In, respectively. The performance is not identical at all wavelengths, however, and the performance of InGaN-based green LEDs is still relatively poor. [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.  Geiger-mode operation of back-illuminated GaN avalanche photodiodes
J. L. Pau, R. McClintock, K. Minder, C. Bayram, P. Kung, M. Razeghi, E. Muñoz, and D. Silversmith
Applied Physics Letters, Vol. 91, No. 04, p. 041104 -1-- July 23, 2007 ...[Visit Journal]
We report the Geiger-mode operation of back-illuminated GaN avalanche photodiodes fabricated on transparent AlN templates specifically for back illumination in order to enhance hole-initiated multiplication. The spectral response in Geiger-mode operation was analyzed under low photon fluxes. Single photon detection capabilities were demonstrated in devices with areas ranging from 225 to 14,063 µm2. Single photon detection efficiency of 20% and dark count rate < 10 kHz were achieved in the smallest devices. [reprint (PDF)]
 
1.  Quantum Sensing Using Type-II InAs/GaSb Superlattice for Infrared Detection
M. Razeghi, A. Gin, Y. Wei, J. Bae, and J. Nah
Microelectronics Journal, 34 (5-8)-- May 1, 2003 ...[Visit Journal]
Large, regular arrays of bulk GaSb and InAs/GaSb Type-II superlattice pillars have been fabricated by electron beam lithography and dry etching. A 2.5 keV electron beam lithography system and metal evaporation are used to form the Au mask on superlattice and bulk substrates. Dry etching of these materials has been developed with BCl3:Ar, CH4:H2:Ar and cyclic CH4:H2:Ar/O2 plasmas. Etch temperatures were varied from 20 to 150 °C. The diameter of the superlattice pillars was below 50 nm with regular 200 nm spacing. Bulk GaSb pillars were etched with diameters below 20 nm. Areas of dense nanopillars as large as 500 μm×500 μm were fabricated. The best height/diameter aspect ratio was approximately 10:1. To date, these are the smallest diameter III–V superlattice pillar structures reported, and the first nanopillars in the InAs/GaSb material system. The basic theory of these devices and surface passivation with SiO2 and Si3N4 thin films has also been discussed. [reprint (PDF)]
 
1.  Short Wavelength Solar-Blind Detectors: Status, Prospects, and Markets
M. Razeghi
IEEE Proceedings, Wide Bandgap Semiconductor Devices: The Third Generation Semiconductor Comes of Age 90 (6)-- June 1, 2002 ...[Visit Journal]
Recent advances in the research work on III-nitride semiconductors and AlxGa1-xN materials in particular has renewed the interest and led to significant progress in the development of ultraviolet (UV) photodetectors able to detect light in the mid- and near-UV spectral region (λ∼200-400 nm). There have been a growing number of applications which require the use of such sensors and, in many of these, it is important to be able to sense UV light without detecting infrared or visible light, especially from the Sun, in order to minimize the chances of false detection or high background. The research work on short-wavelength UV detectors has, therefore, been recently focused on realizing short-wavelength "solar-blind" detectors which, by definition, are insensitive to photons with wavelengths longer than ∼285 nm. In this paper the development of AlxGa1-xN-based solar-blind UV detectors will be reviewed. The technological issues pertaining to material synthesis and device fabrication will be discussed. The current state-of-the-art and future prospects for these detectors will be reviewed and discussed. [reprint (PDF)]
 
1.  Novel Sb-based Alloys for Uncooled Infrared Photodetector Applications
M. Razeghi
SPIE Conference, San Jose, CA, -- January 22, 2001 ...[Visit Journal]
We report on the growth and characterization of InSbBi, InTlSb, InTlP, and the quaternary alloys for uncooled long- wavelength infrared photodetector applications. The layers were grown on InSb and GaAs substrates by low-pressure metalorganic chemical vapor deposition. The incorporation of Bi and Tl in InSb was investigated with high-resolution x-ray diffraction, energy dispersive x-ray analysis, and optical photoresponse measurements. We also demonstrate the photodetectors fabricated from the grown InSbBi and InTlSb alloys. InSb0.96Bi0.04 photoconductive detectors exhibited a responsivity of 3.2 V/W at 77 K. The estimated Johnson noise limited detectivity at 7 micrometers was 1.7 X 108 cm·Hz½/W at 77 K. A room temperature operating InSb0.95Bi0.05 photodetector was also demonstrated. Photoresponse up to 12 micrometers was achieved at 300 K. The responsivity and Johnson noise-limited detectivity at 10.6 μm were 1.9 mV/W and 1.2 X 106 cm·Hz½/W, respectively. Photoresponse up to 15 μm was achieved at 300 K from quaternary InTlAsSb and InBiAsSb alloys. [reprint (PDF)]
 
1.  Interface-induced Suppression of the Auger Recombination in Type-II InAs/GaSb Superlattices
H. Mohseni, V.I. Litvinov and M. Razeghi
Physical Review B 58 (23)-- December 15, 1998 ...[Visit Journal]
The temperature dependence of the nonequilibrium carriers lifetime has been deduced from the measurement of the photocurrent response in InAs/GaSb superlattices. Based on the temperature dependence of the responsivity and modeling of the transport parameters we have found that the carrier lifetime weakly depends on temperature in the high-temperature region. This indicates the temperature dependence of the Auger recombination rate with no threshold that differs it from that in the bulk material and can be attributed to the interface-induced suppression of the Auger recombination in thin quantum wells. [reprint (PDF)]
 
1.  Phase-matched optical second-harmonic generation in GaN and AlN slab waveguides
D.N. Hahn, G.T. Kiehne, G.K.L. Wong, J.B. Ketterson, P. Kung, A. Saxler and M. Razeghi
Journal of Applied Physics 85 (5)-- March 1, 1999 ...[Visit Journal]
Phase-matched optical second-harmonic (SH) generation was observed in GaN and AlN slab waveguides. Phase matching was achieved by waveguide modal dispersion. By tuning the output wavelength of an optical parametric amplifier, several phased-matched SH peaks were observed in the visible spectrum covering blue to red wavelengths. The peak positions are in agreement with the values calculated using the dispersive refractive indices of the film and substrate materials. [reprint (PDF)]
 
1.  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 ...[Visit Journal]
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 (PDF)]
 
1.  The Molecular Beam Epitaxial Growth of InSb on (111) GaAs
E. Michel, J. Kim, J. Xu, S. Javadpour, I. Ferguson, and M. Razeghi
Applied Physics Letters 69 (2)-- July 8, 1996 ...[Visit Journal]
The molecular beam epitaxial growth of InSb on (111)B GaAs has been investigated. It was found that for a given Sb/In ratio, a higher growth temperature was required for the growth of InSb on (111)B GaAs compared to that on (001) GaAs. This difference has been attributed to the bonding characteristics of the (111)B and (001) surface. Once growth had been optimized, it was found that the material characteristics of (111)B InSb were almost identical to that of (001) InSb, i.e., independent of orientation. For example, the x-ray full width at half-maximum and 300 K mobility had the same absolute values for (111) InSb and (001)InSb and followed the same dependence with the sample thickness. Te was found to be a well-behaved n-type dopant for (111)B InSb. [reprint (PDF)]
 
1.  Background Limited Performance in p-doped GaAs/Ga[0.71]In[0.29]As[0.39]P[0.61] Quantum Well Infrared Photodetectors
J. Hoff, S. Kim, M. Erdtmann, R. Williams, J. Piotrowski, E. Bigan, M. Razeghi and G. Brown
Applied Physics Letters 67 (1)-- July 3, 1995 ...[Visit Journal]
Background limited infrared photodetection has been achieved up to 100 K at normal incidence with p-type GaAs/Ga0.71In0.29As0.39P0.61 quantum well intersubband photodetectors grown by low-pressure metalorganic chemical vapor deposition. Photoresponse covers the wavelength range from 2.5 μm up to 7 μm. The device shows photovoltaic response, the cutoff wavelength increases slightly with bias, and the responsivity increases nonlinearly with bias. These effects are attributed to an asymmetric quantum well profile. [reprint (PDF)]
 
1.  Ultraviolet Detectors for AstroPhysics Present and Future
M. Ulmer, M. Razeghi, and E. Bigan
Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 239-- February 6, 1995 ...[Visit Journal]
Astronomical instruments for the study of UV astronomy have been developed for NASA missions such as the Hubble Space Telescope. The systems that are `blind to the visible' (`solar-blind') yet sensitive to the UV that have been flown in satellites have detective efficiencies of about 10 to 20%, although typically electron bombardment charge coupled devices are higher at 30 - 40% and ordinary CCDs achieve 1 - 5%. Therefore, there is a large payoff still to be gained by further improvements in the performance of solar blind UV detectors. We provide a brief review of some aspects of UV astronomy, UV detector development, and possible technologies for the future. We suggest that a particularly promising future technology is one based on the ability of investigators to produce high quality films made of wide bandgap III-V semiconductors. [reprint (PDF)]
 
1.  The correlation between x-ray diffraction patterns and strain distribution inside GaInP/GaAs superlattices
X.G. He, M. Erdtmann, R. Williams, S. Kim, and M. Razeghi
Applied Physics Letters 65 (22)-- November 28, 1994 ...[Visit Journal]
Strong correlation between x‐ray diffraction characteristics and strain distribution inside GaInP/GaAs superlattices has been reported. It is found that the symmetry of (002) diffraction patterns can be used to evaluate the interface strain status. A sample with no interfacial strains has a symmetric (002) diffraction pattern and weak (004) diffraction pattern. It is also demonstrated that strain distribution in superlattices can be readily estimated qualitatively by analyzing x-ray diffraction patterns. [reprint (PDF)]
 
1.  Novel process for direct bonding of GaN onto glass substrates using sacrificial ZnO template layers to chemically lift-off GaN from c-sapphire
Rogers, D. J.; Ougazzaden, A.; Sandana, V. E.; Moudakir, T.; Ahaitouf, A.; Teherani, F. Hosseini; Gautier, S.; Goubert, L.; Davidson, I. A.; Prior, K. A.; McClintock, R. P.; Bove, P.; Drouhin, H.-J.; Razeghi, M.
Proc. SPIE 8263, Oxide-based Materials and Devices III, 82630R (February 9, 2012)-- February 9, 2012 ...[Visit Journal]
GaN was grown on ZnO-buffered c-sapphire (c-Al2O3) substrates by Metal Organic Vapor Phase Epitaxy. The ZnO then served as a sacrificial release layer, allowing chemical lift-off of the GaN from the c-Al2O3 substrate via selective wet etching of the ZnO. The GaN was subsequently direct-wafer-bonded onto a glass substrate. X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray microanalysis, Room Temperature Photoluminescence & optical microscopy confirmed bonding of several mm2 of crack-free wurtzite GaN films onto a soda lime glass microscope slide with no obvious deterioration of the GaN morphology. Using such an approach, InGaN based devices can be lifted-off expensive single crystal substrates and bonded onto supports with a better cost-performance profile. Moreover, the approach offers the possibility of reclaiming and reusing the substrate. [reprint (PDF)]
 
1.  Comparison of ultraviolet APDs grown on free-standing GaN and sapphire substrates
E. Cicek, Z. Vashaei, C. Bayram, R. McClintock, M. Razeghi and M. Ulmer
Proceedings, Vol. 7780, p. 77801P, SPIE Optics and Photonics Symposium, Conference on Detectors and Imaging Devices: Infrared, Focal Plane and Single Photon, San Diego, CA -- August 4, 2010 ...[Visit Journal]
There is a need for semiconductor-based ultraviolet photodetectors to support avalanche gain in order to realize better performance andmore effective compete with existing technologies. Wide bandgap III-Nitride semiconductors are the promising material system for the development of avalanche photodiodes (APDs) that could be a viable alternative to current bulky UV detectors such as photomultiplier tubes. In this paper, we review the current state-of-the-art in IIINitride visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE. [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.  Minority electron unipolar photodetectors based on Type-II InAs/GaSb/AlSb superlattices for very long wavelength infrared detection
B.M. Nguyen, S. Abdollahi Pour, S. Bogdanov and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7608, p. 760825-1-- January 22, 2010 ...[Visit Journal]
The bandstructure tunability of Type-II antimonide-based superlattices has been significantly enhanced since the introduction of the M-structure superlattice, resulting in significant improvements of Type-II superlattice infrared detectors. By using M-structure, we developed the pMp design, a novel infrared photodetector architecture that inherits the advantages of traditional photoconductive and photovoltaic devices. This minority electron unipolar device consists of an M-structure barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. Applied for the very long wavelength detection, at 77K, a 14µm cutoff detector exhibits a dark current 3.3 mA·cm−2, a photoresponsivity of 1.4 A/W at 50mV bias and the associated shot-noise detectivity of 4x1010 Jones. [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.  High-power mid- and far- wavelength infrared lasers for free space communication
M. Razeghi; A. Evans; J. Nguyen; Y. Bai; S. Slivken; S.R. Darvish; K. Mi
Proc. SPIE 6593, Photonic Materials, Devices, and Applications II, 65931V (June 12, 2007)-- June 12, 2007 ...[Visit Journal]
Laser-based free-space communications have been developed to serve specific roles in "last mile" high-speed data networks due to their high security, low cost, portability, and high bandwidth. Conventional free-space systems based on near infrared optical devices suffer from reliability problems due to atmospheric scattering losses and scintillation effects, such as those encountered with storms, dust, and fog. Mid-infrared wavelengths are less affected by atmospheric effects and can significantly enhance link up-time and range. This paper will discuss some of the recent advances in high-power, high temperature, high reliability mid-infrared Quantum Cascade Lasers and their potential application in highly reliable free space communication links. [reprint (PDF)]
 
1.  Positive and negative luminescence in binary Type-II InAs/GaSb superlattice photodiodes
D. Hoffman and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61271H-- January 23, 2006 ...[Visit Journal]
In the present work, we show measurements of both positive and negative luminescence of binary Type-II InAs/GaSb superlattice photodiodes in the 3 to 13 μm spectral range. Through a radiometric calibration technique, we demonstrate temperature independent negative luminescence efficiencies of 45 % in the midwavelength (MWIR) sample from 220 K to 320 K without anti-reflective coating and values reaching 35 % in the long wavelength infrared (LWIR) spectrum sample. [reprint (PDF)]
 
1.  Ridge-Width Dependence on High-Temperature Continuous-Wave Quantum-Cascade Laser Operation
S. Slivken, J.S. Yu, A. Evans, L. Doris, J. David, and M. Razeghi
IEEE Photonics Technology Letters, 16 (3)-- March 1, 2004 ...[Visit Journal]
We report continuous-wave (CW) operation of quantum-cascade lasers (λ=6 μm) up to a temperature of 313 K (40°C). The maximum CW optical output powers range from 212 mW at 288 K to 22 mW at 313 K and are achieved with threshold current densities of 2.21 and 3.11 kA/cm2, respectively, for a high-reflectivity-coated 12-μm-wide and 2-mm-long laser. At room temperature (298 K), the power output is 145 mW at 0.87 A, corresponding to a power conversion efficiency of 1.68%. The maximum CW operating temperature of double-channel ridge waveguide lasers mounted epilayer-up on copper heatsinks is analyzed in terms of the ridge width, which is varied between 12 and 40 μm. A clear trend of improved performance is observed as the ridge narrows. [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)]
 

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