Center for Quantum Devices - Most Downloaded Journal Articles

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21.	Recent advances of terahertz quantum cascade lasers Manijeh Razeghi Proc. SPIE 8119, Terahertz Emitters, Receivers, and Applications II, 81190D (September 07, 2011)-- November 7, 2011 ...[Visit Journal] In the past decade, tremendous development has been made in GaAs/AlGaAs based THz quantum cascade laser (QCLs), however, the maximum operating temperature is still limited below 200 K (without magnetic field). THz QCL based on difference frequency generation (DFG) represents a viable technology for room temperature operation. Recently, we have demonstrated room temperature THz emission (∼ 4 THz) up to 8.5 μW with a power conversion efficiency of 10 μW/W². A dual-period distributed feedback grating is used to filter the mid-infrared spectra in favor of an extremely narrow THz linewidth of 6.6 GHz. [reprint (PDF)]
21.	Anomalous Hall Effect in InSb Layers Grown by MOCVD on GaAs Substrates C. Besikci, Y.H. Choi, R. Sudharsanan, and M. Razeghi Journal of Applied Physics 73 (10)-- May 15, 1993 ...[Visit Journal] InSb epitaxial layers have been grown on GaAs substrates by low‐pressure metalorganic chemical vapor deposition. A 3.15 μm thick film yielded an x‐ray full width at half maximum of 171 arcsec. A Hall mobility of 76 200 cm²/V· s at 240 K and a full width at half maximum of 174 arcsec have been measured for a 4.85 μm thick epilayer. Measured Hall data have shown anomalous behavior. A decrease in Hall mobility with decreasing temperature has been observed and room‐temperature Hall mobility has increased with thickness. In order to explain the anomalous Hall data, and the thickness dependence of the measured parameters, the Hall coefficient and Hall mobility have been simulated using a three‐layer model including a surface layer, a bulklike layer, and an interface layer with a high density of defects. Theoretical analysis has shown that anomalous behavior can be attributed to donor-like defects caused by the large lattice mismatch and to a surface layer which dominates the transport in the material at low temperatures. [reprint (PDF)]
21.	Aluminum-free Quantum Well Intersubband Photodetectors with p-type GaAs Wells and lattice-matched ternary and quaternary barriers J. Hoff, E. Bigan, G.J. Brown, and M. Razeghi Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal] Acceptor doped Quantum Well Intersubband Photodetectors with GaAs wells and lattice matched barriers of both ternary (In_0.49Ga_0.51P) and quaternary (In_0.62Ga_0.38As_0.22P_0.78) materials have been grown on semi-insulating GaAs substrates by Low Pressure Metal Organic Chemical Vapor Deposition. Mesa devices were fabricated and subjected to a series of tests to illuminate experimentally some of the detection capabilities of the lattice matched quaternary InxGa1-xAsyP1-y system with (0 ≤ x ≤ 0.52) and (0 ≤ y ≤ 1). The observed photoresponse cut-off wavelengths are in good agreement with the activation energies observed in the temperature dependence of the dark currents. Kronig-Penney calculations were used to model the intersubband transition energies. [reprint (PDF)]
20.	280 nm UV LEDs Grown on HVPE GaN Substrates A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, M. Razeghi, and R.J. Molnar Opto-Electronics Review, 10 (4)-- January 1, 2002 ...[Visit Journal] We report on the enhancement of optical and electrical properties of 280 nm UV LEDs using low dislocation density HVPE-grown GaN substrate. Compared with the same structure grown on sapphire, these LEDs show ~30% reduction in current-voltage differential resistance, ~15% reduction in turn-on voltage, more than 200% increase in output power slope efficiency and saturation at higher currents. Lower density of defects due to higher material quality and better heat dissipation are believed to be the reason behind these improvements. [reprint (PDF)]
20.	Demonstration of 256x256 Focal Plane Arrays Based on Al-free GaInAs/InP QWIP J. Jiang, K. Mi, R. McClintock, M. Razeghi, G.J. Brown, and C. Jelen IEEE Photonics Technology Letters 15 (9)-- September 1, 2003 ...[Visit Journal] We report the first demonstration of an infrared focal plane array based on aluminum-free GaInAs-InP quantum-well infrared photodetectors (QWIPs).A unique positive lithography method was developed to perform indium-bump liftoff. The noise equivalent differential temperature (NEΔT) of 29 mK was achieved at 70 K with f/2 optics. [reprint (PDF)]
20.	High power continuous operation of a widely tunable quantum cascade laser with an integrated amplifier S. Slivken, S. Sengupta, and M. Razeghi Applied Physics Letters 107, 251101-- December 21, 2015 ...[Visit Journal] Wide electrical tuning and high continuous output power is demonstrated from a single mode quantum cascade laser emitting at a wavelength near 4.8 μm. This is achieved in a space efficient manner by integrating an asymmetric sampled grating distributed feedback tunable laser with an optical amplifier. An initial demonstration of high peak power operation in pulsed mode is demonstrated first, with >5 W output over a 270 nm (113 cm⁻¹) spectral range. Refinement of the geometry leads to continuous operation with a single mode spectral coverage of 300 nm (120 cm⁻¹) and a maximum continuous power of 1.25 W. The output beam is shown to be nearly diffraction-limited, even at high amplifier current. [reprint (PDF)]
20.	High performance InAs quantum dot infrared photodetectors (QDIP) on InP by MOCVD W. Zhang, H. Lim, M. Taguchi, S. Tsao, J. Szafraniec, B. Movaghar, M. Razeghi, and M. Tidrow SPIE Conference, Jose, CA, Vol. 5732, pp. 326-- January 22, 2005 ...[Visit Journal] Inter-subband detectors such as quantum well infrared photodetectors (QWIP) have been widely used in infrared detection. Quantum dot infrared photodetectors (QDIPs) have been predicted to have better performance than QWIPs including higher operation temperature and normal incidence detection. Here we report our recent results of InAs QDIP grown on InP substrate by low-pressure metalorganic chemical vapor deposition (MOCVD). The device structures consist of multiple stacks of InAs quantum dots with InP barriers. High detectivities in the range of 10¹⁰cm·Hz^1/2/W were obtained at 77K. The measurements at higher temperatures show better temperature dependent performance than QWIP. However, the performances of QDIPs are still far from the expected. One of the reasons is the low quantum efficiency due to the low fill factor of quantum dots layer. Resonant cavity enhanced QDIP has been studied to increase the quantum efficiency. Different schemes of mirrors using free carrier plasma and distributed Bragg reflector are discussed. [reprint (PDF)]
20.	Very High Average Power Quantum Cascade Lasers by GasMBE S. Slivken and M. Razeghi SPIE Conference, San Jose, CA, Vol. 4999, pp. 59-- January 27, 2003 ...[Visit Journal] Very high average power QCLs are demonstrated within the 5.8 - 9 µm wavelength range. At longer wavelengths, scaling of the power is demonstrated by increasing the number of emitting regions in the waveguide core. At λ = 9 µm, over 3.5 W of peak power per facet has been demonstrated at room temperature for a single 25 µm by 3 mm diode, with an average power of 150 mW at 6% duty cycle. At shorter wavelengths, highly strain-balanced heterostructures are used to create a high coduction band offset and minimize leakage current. At λ = 6 µm, utilizing a high reflective coating and epilayer-down mounting of the laser, we demonstrate 225 mW of average power from a single facet at room temperature. Increasing the conduction band offset further and optimizing the doping in the injector region has led to demonstration of > 250 mW average power (λ = 5.8 µm) at > 50% duty cycle for a 20 µm by 2 mm HR coated diode bonded epilayer-down to a copper heatsink. Also at room temperature, use of Au electroplating and wider ridges has allowed us to further demonstrate without epilayer-down bonding, 0.67 W average power at 17% duty cycle from a single 40 µm by 2 mm HR coated laser. [reprint (PDF)]
20.	Influence of Residual Impurity Background on the Non-radiative Recombination Processes in High Purity InAs/GaSb superlattice Photodiodes E.C.F. da Silva, D. Hoffman, A. Hood, B. Nguyen, P.Y. Delaunay and M. Razeghi Applied Physics Letters, 89 (24)-- December 11, 2006 ...[Visit Journal] The influence of the impurity background on the recombination processes in type-II InAs/GaSb superlattice photodiodes with a cutoff wavelength of approximately 4.8 μm was investigated by electroluminescence measurements. Using an iterative fitting procedure based on the dependence of the quantum efficiency of the electroluminescence on the injection current, the Auger and Shockley-Read-Hall lifetimes were determined [reprint (PDF)]
20.	Solar-blind avalanche photodiodes R. McClintock, K. Minder, A. Yasan, C. Bayram, F. Fuchs, P. Kung and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 61271D-- January 23, 2006 ...[Visit Journal] There is a need for semiconductor based UV photodetectors to support avalanche gain in order to realize better performance and more effectively compete with existing photomultiplier tubes. However, there are numerous technical issues associated with the realization of high-quality solar-blind avalanche photodiodes (APDs). In this paper, APDs operating at 280 nm, within the solar-blind region of the ultraviolet spectrum, are investigated. [reprint (PDF)]
20.	AlGaN-based deep-ultraviolet 320 x 256 focal plane array E. Cicek, Z. Vashaei, E.K. Huang, R. McClintock and M. Razeghi OSA Optics Letters, Vol. 37, No. 5, p. 896-898-- March 1, 2012 ...[Visit Journal] We report the synthesis, fabrication, and testing of a 320 × 256 focal plane array (FPA) of back-illuminated, solarblind, p-i-n, Al_xGa_1−xN–based detectors, fully realized within our research laboratory. We implemented a pulse atomic layer deposition technique for the metalorganic chemical vapor deposition growth of thick, high-quality, crack-free, high Al composition Al_xGa_1−xN layers. The FPA is hybridized to a matching ISC 9809 readout integrated circuit and operated in a SE-IR camera system. 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. By developing an opaque masking technology, the visible response of the ROIC is significantly reduced; thus the need for external filtering to achieve solar- and visible-blind operation is eliminated. This allows 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)]
20.	Multiple-band, Single-mode, High-power, Phase-locked, Mid-infrared Quantum Cascade Laser Arrays Manijeh Razeghi, Wenjia Zhou, Quanyong Lu, Donghai Wu, and Steven Slivken Imaging and Applied Optics 2018, JTh1A.2-- September 15, 2018 ...[Visit Journal] Single-mode, 16-channel, phase-locked laser arrays based on quantum cascade laser technology are demonstrated at multiple spectral bands across the mid-infrared spectrum region. High peak output power of 50W is achieved around the long-wavelength band of 7.7µm, while a side mode suppression ratio over 25dB is obtained. Far field distribution measurement result indicates a uniform phase distribution across the array output. [reprint (PDF)]
19.	High Optical Response in Forward Biased (In,Ga)N-GaN Multiquantum-Well Diodes Under Barrier Illumination J.L. Pau, R. McClintock, C. Bayram, K. Minder, D. Silversmith and M. Razeghi IEEE Journal of Quantum Electronics, Vol. 44, No. 4, p. 346-353.-- April 1, 2008 ...[Visit Journal] The authors report on the current–voltage (I–V) characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N–GaN-n multiquantum well diodes. Under barrier illumination, the devices present a high optical response with capabilities to detect optical powers in the pW range without further amplification. This response is attributed to the screening of the internal electric fields. Recombination times of a few seconds are found to be associated to this mechanism. Moreover, a step-like feature is found in the I– V characteristic before the diode turn-on voltage. Our model proposes tunneling current through the multi-quantum-well structure as responsible of this feature. Fast modulation of the tunneling effect under barrier illumination is used to evaluate the detection of low photon fluxes. [reprint (PDF)]
19.	Aluminum free GaInP/GaAs Quantum Well Infrared Photodetectors for Long Wavelength Detection C. Jelen, S. Slivken, J. Hoff, M. Razeghi, and G. Brown Applied Physics Letters 70 (3)-- January 20, 1997 ...[Visit Journal] We demonstrate quantum well infrared photodetectors based on a GaAs/Ga_0.51In_0.49P superlattice structure grown by gas-source molecular beam epitaxy. Wafers were grown with varying well widths. Wells of 40, 65, and 75 Å resulted in peak detection wavelengths of 10.4, 12.8, and 13.3 μm with a cutoff wavelength of 13.5, 15, and 15.5 μm, respectively. The measured peak and cutoff wavelengths match those predicted by eight band theoretical analysis. Measured dark currents were lower than equivalent GaAs/AlGaAs samples. [reprint (PDF)]
19.	Electroluminescence of InAs/GaSb heterodiodes D. Hoffman, A. Hood, E. Michel, F. Fuchs, and M. Razeghi IEEE Journal of Quantum Electronics, 42 (2)-- February 1, 2006 ...[Visit Journal] The electroluminescence of a Type-II InAs-GaSb superlattice heterodiode has been studied as a function of injection current and temperature in the spectral range between 3 and 13 μm. The heterodiode comprises a Be-doped midwavelength infrared (MWIR) superlattice with an effective bandgap around 270 meV and an undoped long wavelength infrared (LWIR) superlattice with an effective bandgap of 115 meV. [reprint (PDF)]
19.	Nickel oxide growth on Si (111), c-Al₂O₃ and FTO/glass by pulsed laser deposition V. E. Sandana ; D. J. Rogers ; F. Hosseini Teherani ; P. Bove ; R. McClintock ; M. Razeghi 03/07/2014-- March 7, 2014 ...[Visit Journal] NiO was grown on Si (111), c-Al₂O₃ and FTO/glass substrates by pulsed laser deposition (PLD). X-Ray Diffraction (XRD) and scanning electron microscope (SEM) studies revealed that layers grown on c-Al₂O₃ were fcc NiO with a dense morphology of cubic grains that were strongly (111) oriented along the growth direction. The relatively low ω rocking curve linewidth, of 0.12°suggests that there may have been epitaxial growth on the c-Al₂O₃ substrate. XRD and SEM indicated that films grown on Si (111) were also fcc NiO, with cubic grains, but that the grain orientation was random. This is consistent with the presence of an amorphous SiO₂ layer at the surface of the Si substrate, which precluded epitaxial growth. NiO grown at lower temperature (200°C) on temperature-sensitive FTO/glass substrates showed no evidence of crystallinity in XRD and SEM studies. After flash annealing in air, however, peaks characteristic of randomly oriented fcc NiO appeared in the XRD scans and the surface morphology became more granular in appearance. Such layers appear promising for the development of future dye-sensitised solar cell devices based on NiO grown by PLD. [reprint (PDF)]
19.	Infrared detection from GaInAs/InP nanopillar arrays A. Gin, B. Movaghar, M. Razeghi and G.J. Brown Nanotechnology 16-- July 1, 2005 ...[Visit Journal] We report on the photoresponse from large arrays of 40 nm radius nanopillars with sensitivity in the long-wavelength infrared regime. Using photoluminescence techniques, a peak wavelength blue shift of approximately 5 meV was observed at 30 K from GaInAs/InP nanopillar structures, indicating carrier confinement effects. Responsivity measurements at 30 K indicated peak wavelength response at about 8 µm with responsivity of 420 mA/W at −2 V bias. We have also measured the noise and estimated the peak detectivity to be 3×10⁸ cm·Hz^½·W⁻¹ at 1 V reverse bias and 30 K. A maximum internal quantum efficiency of 4.5% was derived from experiment. Both the photo and the dark transport have been successfully modeled as processes that involve direct and indirect field-assisted tunneling as well as thermionic emission. The best agreement with experiment was obtained when allowances were made for the non-uniformity of barrier widths and electric field heating of carriers above the lattice temperature. [reprint (PDF)]
19.	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)]
19.	Direct growth of thick AlN layers on nanopatterned Si substrates by cantilever epitaxy Ilkay Demir, Yoann Robin, Ryan McClintock, Sezai Elagoz, Konstantinos Zekentes, and Manijeh Razeghi Physica Status Solidi 214 (4), pp. 1770120-- April 4, 2017 ...[Visit Journal] The growth of thick, high quality, and low stress AlN films on Si substrates is highly desired for a number of applications like the development of micro and nano electromechanical system (MEMS and NEMS) technologies [1] and particularly for fabricating AlGaNbased UV LEDs [2–5]. UV LEDs are attractive as they are applied in many areas, such as biomedical instrumentations and dermatology, curing of industrial resins and inks, air purification, water sterilization, and many others [2, 3]. UV LEDs have been generally fabricated on AlN, GaN, Al₂O₃, or SiC substrates because of better lattice mismatching to AlGaN material systems. [reprint (PDF)]
19.	High Performance Quantum Cascade Lasers Grown by Gas-Source Molecular Beam Epitaxy M. Razeghi, S. Slivken, A. Tahraoui and A. Matlis SPIE Conference, San Jose, CA, -- January 22, 2001 ...[Visit Journal] Recent improvements in quantum cascade laser technology have led to a number of very impressive results. This paper is a brief summary of the technological development and state-of- the-art performance of quantum cascade lasers produced at the Center for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Room temperature QCL operation has been reported for lasers emitting between 5 - 11 μm, with 9 - 11 μm lasers operating up to 425 K. We also demonstrate record room temperature peak output powers at 9 and 11 μm(2.5 W and 1 W respectively) as well as record low 80 K threshold current densities (250 A/cm²) for some laser designs. Finally, some of the current limitations to laser efficiency are mentioned, as well as a means to combat them. [reprint (PDF)]
19.	High efficiency quantum cascade laser frequency comb Quanyong Lu, Donghai Wu, Steven Slivken & Manijeh Razeghi Scientific Reports 7, Article number: 43806-- March 6, 2017 ...[Visit Journal] An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. Here we demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The active region was designed with a strong-coupling between the injector and the upper lasing level for high internal quantum efficiency and a broadband gain. The group velocity dispersion was engineered for efficient, broadband mode-locking via four wave mixing. The comb device exhibits a narrow intermode beatnote linewidth of 50.5 Hz and a maximum wall-plug efficiency of 6.5% covering a spectral coverage of 110 cm⁻¹ at λ ~ 8 μm. The efficiency is improved by a factor of 6 compared with previous demonstrations. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy. [reprint (PDF)]
19.	Advances in mid-infrared detection and imaging: a key issues review Manijeh Razeghi and Binh-Minh Nguyen Rep. Prog. Phys. 77 (2014) 082401-- August 4, 2014 ...[Visit Journal] It has been over 200 years since people recognized the presence of infrared radiation, and developed methods to capture this signal. However, current material systems and technologies for infrared detections have not met the increasing demand for high performance infrared detectors/cameras, with each system having intrinsic drawbacks. Type-II InAs/GaSb superlattice has been recently considered as a promising candidate for the next generation of infrared detection and imaging. Type-II superlattice is a man-made crystal structure, consisting of multiple quantum wells placed next to each other in a controlled way such that adjacent quantum wells can interact. The interaction between multiple quantum wells offers an additional degree of freedom in tailoring the material's properties. Another advantage of type-II superlattice is the experimental benefit of inheriting previous research on material synthesis and device fabrication of bulk semiconductors. It is the combination of these two unique strengths of type-II superlattice—novel physics and easy manipulation—that has enabled unprecedented progress in recent years. In this review, we will describe historical development, and current status of type-II InAs/GaSb superlattice for advanced detection and imaging in the mid-infrared regime (λ = 3–5 µm). [reprint (PDF)]
19.	Room temperature operation of In_xGa_1-xSb/InAs type-II quantum well infrared photodetectors grown by MOCVD D. H. Wu, Y. Y. Zhang, and M. Razeghi Applied Physics Letters 112, 111103-- March 14, 2018 ...[Visit Journal] We demonstrate room temperature operation of In_0.5Ga_0.5Sb/InAs type-II quantum well photodetectors on InAs substrate grown by metal-organic chemical vapor deposition. At 300 K, the detector exhibits a dark current density of 0.12 A/cm², peak responsivity of 0.72 A/W corresponding to a quantum efficiency of 23.3%, with calculated specific detectivity of 2.4×10⁹ cm.Hz^1/2/W at 3.81 μm. [reprint (PDF)]
19.	High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 μm WENJIA ZHOU,QUAN-YONG LU,DONG-HAI WU, STEVEN SLIVKEN, AND MANIJEH RAZEGHI OPTICS EXPRESS 27, 15776-15785-- May 20, 2019 ...[Visit Journal] We report a room-temperature eight-element phase-locked quantum cascade laser array emitting at 8 μm with a high continuous-wave power of 8.2 W and wall plug efficiency of 9.5%. The laser array operates primarily via the in-phase supermode and has single-mode emission with a side-mode suppression ratio of ~20 dB. The quantum cascade laser active region is based on a high differential gain (8.7 cm/kA) and low voltage defect (90 meV) design. A record high wall plug efficiency of 20.4% is achieved from a low loss buried ridge type single-element Fabry-Perot laser operating in pulsed mode at 20 °C. [reprint (PDF)]
19.	Novel Method for Reclaim/Reuse of Bulk GaN Substrates using Sacrifical ZnO Release Layers A. Rajan, S. Sundaram, Y. El Gmili, P. L. Voss, K. Pantzas, T. Moudakir, A. Ougazzaden, D. J. Rogers, F. Hosseini Teherani, V. E. Sandana, P. Bove, K. Prior, R. McClintock & M. Razeghi Proc. SPIE 8987, Oxide-based Materials and Devices V, 898719-- April 2, 2014 ...[Visit Journal] Free-standing (0002)-oriented GaN substrates (f = 2”) were coated with 200 nm of ZnO and used as templates for the growth of GaN thin films. SEM and AFM revealed that such GaN layers had a relatively homogenous surface morphology with an RMS roughness (5 μm x 5 μm) of less than 4nm. XRD studies revealed strained ZnO growth on the GaN substrate and the reproduction of the substrate rocking curve for the GaN overlayers after only a hundred nm of growth, thus indicating that the GaN films had superior crystallographic quality compared to those grown on sapphire or ZnO/sapphire substrates. Quarter-wafer areas of GaN were removed from the GaN substrate (by selective chemical etching away of the ZnO interlayer). The expensive GaN substrates were then reclaimed/reused (without the need for polishing) for a second cycle of ZnO and GaN growth, which gave similar XRD, SEM, CL and AFM results to the first cycle. [reprint (PDF)]

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