Center for Quantum Devices - Most Downloaded Journal Articles

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19.	High quantum efficiency mid-wavelength infrared type-II InAs/InAs_1-xSb_x superlattice photodiodes grown by metal-organic chemical vapor deposition Donghai Wu , Quentin Durlin, Arash Dehzangi , Yiyun Zhang , and Manijeh Razeghi Appl. Phys. Lett. 114, 011104-- January 8, 2019 ...[Visit Journal] We report the growth and characterization of mid-wavelength infrared type-II InAs/InAs_1-xSb_x superlattice photodiodes on GaSb substrates grown by metal-organic chemical vapor deposition. At 150 K, the 50% cut-off wavelength is 5.0 um, the dark current density is 3.3x10⁻⁴ A/cm² under −20mV bias, and the peak responsivity is 1.76A/W corresponding to a quantum efficiency of 55% without anti-reflection coating. A specific detectivity of 1.2x10¹¹cmHz^1/2/W is achieved at 4.0 um under −20mV bias at 150 K. [reprint (PDF)]
19.	Improved performance of IR photodetectors with 3D gap engineering J. Piotrowski and M. Razeghi Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal] The ultimate signal-to-noise performance of the semiconductor photodetector is limited by the statistical fluctuations of the thermal generation and recombination rates in photodetector material. Cooling is an effective but impractical way of suppression of the thermal processes. The performance of uncooled detectors can be improved by minimizing the thermal generation and recombination rates and reducing the actual volume of photodetector. This can be realized in 3D heterostructure devices. In these devices, the incident radiation is absorbed in small regions of narrow gap semiconductor, buried in wide gap volume and supplied with wide gap electric contacts and radiation concentrators. The practical near room-temperature 1 - 12 μm IR heterostructure photodetectors are reported. The devices are based on variable gap Hg_1-xCd_xTe. The 3D heterostructures have been obtained by Isothermal Vapor Growth Epitaxy in a reusable growth system which enables in situ doping during growth with foreign impurities. Ion milling was extensively used in preparation of the devices. Monolithic optical immersion has been applied for further improvement of performance. The 3D heterostructure devices exhibit performance exceeding that of conventional photodetectors. [reprint (PDF)]
19.	Generation-recombination and trap-assisted tunneling in long wavelength infrared minority electron unipolar photodetectors based on InAs/GaSb superlattice F. Callewaert, A.M. Hoang, and M. Razeghi Applied Physics Letters, 104, 053508 (2014)-- February 6, 2014 ...[Visit Journal] A long wavelength infrared minority electron unipolar photodetector based on InAs/GaSb type-II superlattices is demonstrated. At 77 K, a dark current of 3 × 10⁻⁵ A/cm² and a differential resistance-area of 3 700 Ω·cm² are achieved at the turn-on bias, with a 50%-cutoff of 10.0 μm and a specific detectivity of 6.2 × 10¹¹ Jones. The dark current is fitted as a function of bias and temperature using a model combining generation-recombination and trap-assisted tunneling. Good agreement was observed between the theory and the experimental dark current. [reprint (PDF)]
19.	Very Long Wavelength GaAs/GaInP Quantum Well Infrared Photodetectors C. Jelen, S. Slivken, G.J. Brown, and M. Razeghi SPIE Conference, San Jose, CA, -- February 12, 1997 ...[Visit Journal] We demonstrate long wavelength quantum well infrared photodetectors with GaAs quantum wells and GaInP barriers grown using gas-source molecular beam epitaxy. Wafers were grown with varying well widths. The optimum well width was 75 angstrom, which resulted in a detection peak at 13 μm and a cutoff wavelength of 15 μm. Dark current measurements of the samples with 15 μm cutoff wavelength show low dark current densities. The dark current characteristics have been investigated as a function of temperature and electron density in the well and compared to a model which takes into account thermionic emission and thermally assisted tunneling. The model is used to extract a saturation velocity of 1.5 x 10⁵ cm/s for electrons. The photoelectron lifetime before recapture has been deduced from this carrier velocity and photoconductive gain measurements. The lifetime is found to be approximately 5 ps. Preliminary focal plane array imaging is demonstrated. [reprint (PDF)]
19.	Room temperature neagtive differential resistance characteristics of polar III-nitride resonant tunneling diodes C. Bayram, Z. Vashaei, and M. Razeghi Applied Physics Letters, Vol. 97, No. 9, p. 092104-1-- August 30, 2010 ...[Visit Journal] III-nitride resonant tunneling diodes (RTDs), consisting Al_0.2Ga_0.8N/GaN double-barrier (DB) active layers, were grown on c-plane lateral epitaxial overgrowth (LEO) GaN/sapphire and c-plane freestanding (FS) GaN. RTDs on both templates, fabricated into mesa diameters ranging from 5 to 35 μm, showed negative differential resistance (NDR) at room temperature. NDR characteristics (voltage and current density at NDR onset and current-peak-to-valley ratio) were analyzed and reported as a function of device size and substrate choice. Our results show that LEO RTDs perform as well as FS ones and DB active layer design and quality have been the bottlenecks in III-nitride RTDs. [reprint (PDF)]
19.	III-Nitride Optoelectronic Devices: From Ultraviolet Toward Terahertz M. Razeghi IEEE Photonics Journal-Breakthroughs in Photonics 2010, Vol. 3, No. 2, p. 263-267-- April 26, 2011 ...[Visit Journal] We review III-Nitride optoelectronic device technologies with an emphasis on recent breakthroughs. We start with a brief summary of historical accomplishments and then report the state-of-the-art in three key spectral regimes: (1) Ultraviolet (AlGaN-based avalanche photodiodes, single photon detectors, focal plane arrays, and light emitting diodes), (2) Visible (InGaN-based solid state lighting, lasers, and solar cells), and (3) Near-, mid-infrared, and terahertz (AlGaN/GaN-based gap-engineered intersubband devices). We also describe future trends in III-Nitride optoelectronic devices. [reprint (PDF)]
19.	Compressively-strained multiple quantum well InAsSb lasers emitting at 3.6 μm grown by metal-organic chemical vapor deposition B. Lane, D. Wu, A. Rybaltowski, H. Yi, J. Diaz, and M. Razeghi Applied Physics Letters 70 (4)-- January 27, 1997 ...[Visit Journal] A compressively strained InAsSb/InAs multiple quantum-well (MQW) structure was grown by low-pressure metal-organic chemical vapor deposition. Maximum output power (from two facets) up to 1 W with differential efficiency about 70% was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.65 μm at 90 K in pulse mode operation. About 2 times lower threshold current density was obtained from the MQW lasers for a temperature range of 90 to 140 K compared to the double heterostructure lasers grown on the same growth conditions. [reprint (PDF)]
19.	High Power Electrically Injected Mid-Infrared Interband Lasers Grown by LP-MOCVD B. Lane and M. Razeghi Journal of Crystal Growth 221 (1-4)-- December 1, 2000[reprint (PDF)]
19.	Growth and characterization of InSbBi for long wavelength infrared photodetectors J.J. Lee, J.D. Kim, and M. Razeghi Applied Physics Letters 70 (24)-- June 16, 1997 ...[Visit Journal] The epitaxial growth of InSbBi ternary alloys by low-pressure metalorganic chemical vapor deposition is reported on. X-ray diffraction spectra showed well resolved peaks of InSbBi and InSb films. Bi incorporation was confirmed by energy dispersive x-ray analysis. Photoresponse spectrum up to 9.3 μm which corresponds to 0.13 eV energy band gap has been measured in a sample with Bi composition of 5.8 at.% at 77 K. Electron mobility at room temperature ranges from 44 100 to 4910 cm²/V·s as Bi composition increases. [reprint (PDF)]
19.	Shortwave quantum cascade laser frequency comb for multi-heterodyne spectroscopy Q. Y. Lu, S. Manna, D. H. Wu, S. Slivken, and M. Razeghi Applied Physics Letters 112, 141104-- April 3, 2018 ...[Visit Journal] Quantum cascade lasers (QCLs) are versatile light sources with tailorable emitting wavelengths covering the mid-infrared and terahertz spectral ranges. When the dispersion is minimized, frequency combs can be directly emitted from quantum cascade lasers via four-wave mixing. To date, most of the mid-infrared quantum cascade laser combs are operational in a narrow wavelength range wherein the QCL dispersion is minimal. In this work, we address the issue of very high dispersion for shortwave QCLs and demonstrate 1-W dispersion compensated shortwave QCL frequency combs at λ~5.0 μm, spanning a spectral range of 100 cm⁻¹. The multi-heterodyne spectrum exhibits 95 equally spaced frequency comb lines, indicating that the shortwave QCL combs are ideal candidates for high-speed high-resolution spectroscopy [reprint (PDF)]
19.	Extended short wavelength infrared heterojunction phototransistors based on type II superlattices Arash Dehzangi , Ryan McClintock, Donghai Wu , Abbas Haddadi, Romain Chevallier , and Manijeh Razeghi Applied Physics Letters 114, 191109-- May 17, 2019 ...[Visit Journal] A two terminal extended short wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb on a GaSb substrate is designed, fabricated, and investigated. With the base thickness of 40 nm, the device exhibited a 100% cut-off wavelength of 2.3 λ at 300 K. The saturated peak responsivity value is 320.5 A/W at 300 K, under front-side illumination without any antireflection coating. A saturated optical gain of 245 at 300K was measured. At the same temperature, the device exhibited a collector dark current density (at unity optical gain) and a DC current gain of 7.8 X 10³ A/cm² and 1100, respectively. The device exhibited a saturated dark current shot noise limited specific detectivity of 4.9 X 10¹¹ cm·Hz^½/W at 300 K which remains constant over a broad range of wavelengths and applied biases. [reprint (PDF)]
19.	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 ...[Visit Journal] 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. Al_xGa_1-xN is a promising material system for such devices. Al_xGa_1-xN materials are wide bandgap semiconductors, with a direct bandgap whose corresponding wavelength can be continuously tuned from 200 to 365 nm. Al_xGa_1-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 Al_xGa_1-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 (PDF)]
19.	Solar-blind photodetectors and focal plane arrays based on AlGaN R. McClintock, M. Razeghi Proc. SPIE 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications, 955502-- August 25, 2015 ...[Visit Journal] III-Nitride material system (AlGaInN) possesses unique optical, electrical and structural properties such as a wide tunable direct bandgap, inherent fast carrier dynamics; good carrier transport properties, high breakdown fields; and high robustness and chemical stability. Recent technological advances in the wide bandgap AlGaN portion of this material system have led to a renewed interest in ultraviolet (UV) photodetectors. These detectors find use in numerous applications in the defense, commercial and scientific arenas such as covert space-to-space communications, early missile threat detection, chemical and biological threat detection and spectroscopy, flame detection and monitoring, UV environmental monitoring, and UV astronomy.1,2,3 Back illuminated detectors operating in the solar blind region are of special interest. Back illumination allows the detector to be hybridized to a silicon read-out integrated circuit, epi-side down, and still collect light through the back of the transparent sapphire substrate. This allows the realization of solar blind focal plane arrays (FPAs) for imaging applications. Solar-blind FPAs are especially important because of the near total absence of any background radiation in this region. In this talk, we will present our recent back-illuminated solar-blind photodetector, mini-array, and FPA results. By systematically optimizing the design of the structure we have realized external quantum efficiencies (EQE) of in excess of 89% for pixel-sized detectors. Based on the absence of any anti-reflection coating, this corresponds to nearly 100% internal quantum efficiency. At the same time, the dark current remains below ~2 × 10^-9 A/cm² even at 10 volts of reverse bias. The detector has a very sharp falloff starting at 275 with the UV-solar rejection of better than three orders of magnitude, and a visible rejection ratio is more than 6 orders of magnitude. This high performance photodetector design was then used as the basis of the realization of solar-blind FPA. We demonstrated a 320×256 FPA with a peak detection wavelength of 278nm. The operability of the FPA was better than 92%, and excellent corrected imaging was obtained. [reprint (PDF)]
19.	p-doped GaAs/Ga_0.51In_0.49P quantum well intersub-band photodetectors J. Hoff, X. He, M. Erdtmann, E. Bigan, M. Razeghi, and G.J. Brown Journal of Applied Physics 78 (3)-- August 1, 1995 ...[Visit Journal] Lattice‐matched p-doped GaAs–Ga_0.51In_0.49P quantum well intersub‐band photodetectors with three different well widths have been grown on GaAs substrates by metal‐organic chemical‐vapor deposition and fabricated into mesa structures. The photoresponse cutoff wavelength varies between 3.5 and 5.5 μm by decreasing the well width from 50 down to 25 Å. Dark current measurements as a function of temperature reveal activation energies for thermionic emission that closely correspond to measured cutoff wavelengths. Experimental results are in reasonable agreement with Kronig–Penney calculations. [reprint (PDF)]
19.	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)]
19.	Persistent photoconductivity and the quantized Hall effect in In0.53Ga0.47As/InP heterostructures H. P. Wei; D. C. Tsui; M. Razeghi H. P. Wei, D. C. Tsui, M. Razeghi; Persistent photoconductivity and the quantized Hall effect in In0.53Ga0.47As/InP heterostructures. Appl. Phys. Lett. 15 September 1984; 45 (6): 666–668.-- September 15, 1984 ...[Visit Journal] A persistent photoconductivity is observed in the transport of the high mobility two‐dimensional electron gas in In0.53Ga0.47 As/InP heterostructures. Low field Hall measurements from 300 to 4.2 K and the quantized Hall effect in the high field limit are studied with radiation from visible and infrared light‐emitting diodes. Our results demonstrate conclusively that the effect is due to photogeneration of electron‐hole pairs in the heterostructure and trapping of holes in the In0.53Ga0.47 As. [reprint (PDF)]
19.	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)]
19.	Investigation of impurities in type-II InAs/GaSb superlattices via capacitance-voltage measurement G. Chen, A. M. Hoang, S. Bogdanov, A. Haddadi, P. R. Bijjam, B.-M. Nguyen, and M. Razeghi Applied Physics Letters 103, 033512 (2013)-- July 17, 2013 ...[Visit Journal] Capacitance-voltage measurement was utilized to characterize impurities in the non-intentionally doped region of Type-II InAs/GaSb superlattice p-i-n photodiodes. Ionized carrier concentration versus temperature dependence revealed the presence of a kind of defects with activation energy below 6 meV and a total concentration of low 10¹⁵ cm⁻³. Correlation between defect characteristics and superlattice designs was studied. The defects exhibited a p-type behavior with decreasing activation energy as the InAs thickness increased from 7 to 11 monolayers, while maintaining the GaSb thickness of 7 monolayers. With 13 monolayers of InAs, the superlattice became n-type and the activation energy deviated from the p-type trend. [reprint (PDF)]
19.	High operating temperature 320 x 256 middle-wavelength infrared focal plane array imaging based on an InAs/InGaAs/InAlAs/InP quantum dot infrared photodetector S. Tsao, H. Lim, W. Zhang, and M. Razeghi Virtual Journal of Nanoscale Science and Technology-- May 28, 2007 ...[Visit Journal][reprint (PDF)]
19.	Room temperature compact THz sources based on quantum cascade laser technology M. Razeghi; Q.Y. Lu; N. Bandyopadhyay; S. Slivken; Y. Bai Proc. SPIE 8846, Terahertz Emitters, Receivers, and Applications IV, 884602 (September 24, 2013)-- November 24, 2013 ...[Visit Journal] We present the high performance THz sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers. Room temperature single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Čerenkov phase-matched THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via epi-down mounting of our THz device. The rapid development renders this type of THz sources promising local oscillators for many astronomical and medical applications. [reprint (PDF)]
19.	Sandwich method to grow high quality AlN by MOCVD Demir , H Li, Y Robin, R McClintock, S Elagoz and M Razeghi Journal of Physics D: Applied Physics 51, pp. 085104-- February 7, 2018 ...[Visit Journal] We report pulsed atomic layer epitaxy growth of a very high crystalline quality, thick (~2 µm) and crack-free AlN material on c-plane sapphire substrates via a sandwich method using metal organic chemical vapor deposition. This sandwich method involves the introduction of a relatively low temperature (1050 °C) 1500 nm thick AlN layer between two 250 nm thick AlN layers which are grown at higher temperature (1170 °C). The surface morphology and crystalline quality remarkably improve using this sandwich method. A 2 µm thick AlN layer was realized with 33 arcsec and 136 arcsec full width at half maximum values for symmetric and asymmetric reflections of ω-scan, respectively, and it has an atomic force microscopy root-mean-square surface roughness of ~0.71 nm for a 5 × 5 µm² surface area. [reprint (PDF)]
19.	A hybrid green light-emitting diode comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN C. Bayram, F. Hosseini Teherani, D.J. Rogers and M. Razeghi Applied Physics Letters, Vol. 93, No. 8, p. 081111-1-- August 25, 2008 ...[Visit Journal] Hybrid green light-emitting diodes (LEDs) comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN were grown on semi-insulating AlN/sapphire using pulsed laser deposition for the n-ZnO and metal organic chemical vapor deposition for the other layers. X-ray diffraction revealed that high crystallographic quality was preserved after the n-ZnO growth. LEDs showed a turn-on voltage of 2.5 V and a room temperature electroluminescence (EL) centered at 510 nm. A blueshift and narrowing of the EL peak with increasing current was attributed to bandgap renormalization. The results indicate that hybrid LED structures could hold the prospect for the development of green LEDs with superior performance. [reprint (PDF)]
19.	*High quality AlN and GaN epilayers grown on (001) sapphire, (100) and (111) silicon substrates P. Kung, A. Saxler, X. Zhang, D. Walker, T.C. Wang, I. Ferguson, and M. Razeghi Applied Physics Letters 66 (22)-- May 29, 1995** ...[Visit Journal] The growth of high quality AlN and GaN thin films on basal plane sapphire, (100), and (111) silicon substrates is reported using low pressure metalorganic chemical vapor deposition. X-ray rocking curve linewidths of about 100 and 30 arcsec were obtained for AlN and GaN on sapphire, respectively. Room‐temperature optical transmission and photoluminescence (of GaN) measurements confirmed the high quality of the films. The luminescence at 300 and 77 K of the GaN films grown on basal plane sapphire, (100), and (111) silicon was compared. [reprint (PDF)]
19.	High Temperature Continuous Wave Operation of ~8 μm Quantum Cascade Lasers S. Slivken, A. Matlis, C. Jelen, A. Rybaltowski, J. Diaz, and M. Razeghi Applied Physics Letters 74 (2)-- January 11, 1999 ...[Visit Journal] We report single-mode continuous-wave operation of a λ∼8 μm quantum cascade laser at 140 K. The threshold current density is 4.2 kA/cm² at 300 K in pulsed mode and 2.5 kA/cm² at 140 K in continuous wave for 2 mm long index-guided laser cavities of 20 μm width. Wide stripe (W ∼ 100 μm), index-guided lasers from the same wafer in pulsed operation demonstrate an average T₀ of 210 K with other wafers demonstrating a T₀ as high as 290 K for temperatures from 80 to 300 K. This improvement in high-temperature performance is a direct result of three factors: excellent material quality, a low-loss waveguide design, and a low-leakage index-guided laser geometry. [reprint (PDF)]
19.	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)]

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