Center for Quantum Devices - Most Downloaded Journal Articles

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11.	Electroluminescence at 375 nm from a Zn0/GaN:Mg/c-Al₂O₃ heterojunction light emitting diodes D.J. Rogers, F.Hosseini Teherani, A. Yasan, K. Minder, P. Kung, and M. Razeghi Applied Physics Letters, 88 (14)-- April 13, 2006 ...[Visit Journal] n-ZnO/p-GaN:Mg heterojunction light emitting diode (LED) mesas were fabricated on c-Al₂O₃ substrates using pulsed laser deposition for the ZnO and metal organic chemical vapor deposition for the GaN:Mg. Room temperature (RT) photoluminescence (PL) showed an intense main peak at 375 nm and a negligibly low green emission indicative of a near band edge excitonic emission from a ZnO layer with low dislocation/defect density. The LEDs showed I-V characteristics confirming a rectifying diode behavior and a RT electroluminescence (EL) peaked at about 375 nm. [reprint (PDF)]
11.	Optical Absorption and Photoresponse in fully Quaternary p-type Quantum Well Detectors J. Hoff, C. Jelen, S. Slivken, G.J. Brown, and M. Razeghi SPIE Photonics West '96 Photodetectors: Materials and Devices; Proceedings 2685-- January 27, 1996 ...[Visit Journal] Acceptor doped, non-strained aluminum-free Quantum Well Intersubband Photodetectors lattice matched to GaAs with Ga_0.79In_0.21As_0.59P_0.41 wells and Ga_0.62In_0.38As_0.22P_0.78 barriers have been demonstrated on semi-insulating GaAs substrates. These devices which operate at normal incidence demonstrate a unique spectral response which extends from approximately 2 μm up to 10 μm. To explain such a broad spectral shape, a detailed theoretical analysis based on the 8 x 8 Kane Hamiltonian was necessary to probe all aspect of optical absorption. The results of this analysis revealed that spectral shape results from the influence of the Spin Split-off band on the band structure and the optical matrix. [reprint (PDF)]
11.	Effects of well width and growth temperature on optical and structural characteristics of AlN/GaN superlattices grown by metal-organic chemical vapor deposition C. Bayram, N. Pere-Laperne, and M. Razeghi Applied Physics Letters, Vol. 95, No. 20, p. 201906-1-- November 16, 2009 ...[Visit Journal] AlN/GaN superlattices (SLs) employing various well widths (from 1.5 to 7.0 nm) are grown by metal-organic chemical vapor deposition technique at various growth temperatures (Ts) (from 900 to 1035 °C). The photoluminescence (PL), x-ray diffraction, and intersubband (ISB) absorption characteristics of these SLs and their dependency on well width and growth temperature are investigated. Superlattices with thinner wells (grown at the same Ts) or grown at lower Ts (employing the same well width) are shown to demonstrate higher strain effects leading to a higher PL energy and ISB absorption energy. Simulations are employed to explain the experimental observations. ISB absorptions from 1.04 to 2.15 µm are demonstrated via controlling well width and growth temperature. [reprint (PDF)]
11.	Highly temperature insensitive quantum cascade lasers Y. Bai, N. Bandyopadhyay, S. Tsao, E. Selcuk, S. Slivken and M. Razeghi Applied Physics Letters, Vol. 97, No. 25-- December 20, 2010 ...[Visit Journal] An InP based quantum cascade laser (QCL) heterostructure emitting around 5 μm is grown with gas-source molecular beam epitaxy. The QCL core design takes a shallow-well approach to maximize the characteristic temperatures, T(0) and T(1), for operations above room temperature. A T(0) value of 383 K and a T(1) value of 645 K are obtained within a temperature range of 298–373 K. In room temperature continuous wave operation, this design gives a single facet output power of 3 W and a wall plug efficiency of 16% from a device with a cavity length of 5 mm and a ridge width of 8 μm. [reprint (PDF)]
11.	High-power continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ~ 7.8 µm S.R. Darvish, W. Zhang, A. Evans, J.S. Yu, S. Slivken, and M. Razeghi Applied Physics Letters, 89 (25)-- December 18, 2006 ...[Visit Journal] The authors present high-power continuous-wave (cw) operation of distributed-feedback quantum-cascade lasers. Continuous-wave output powers of 56 mW at 25 °C and 15 mW at 40 °C are obtained. Single-mode emission near 7.8 μm with a side-mode suppression ratio of >=30 dB and a tuning range of 2.83 cm⁻¹ was obtained between 15 and 40 °C. The device exhibits no beam steering with a full width at half maximum of 27.4° at 25 °C in cw mode. [reprint (PDF)]
11.	Pressure-induced depopulation of the first excited subband in GaInAs/InP heterojunctions D Gauthier, J C Portal and M Razeghi D Gauthier et al 1989 Semicond. Sci. Technol. 4 218-- December 8, 1988 ...[Visit Journal] Following our previous work on (GalnAs)/(lnP) heterojunctions under hydrostatic pressure we present recent experimental results where the evidence for the total depopulation of the first excited electric subband with pressure is demonstrated. The total electron concentration decreases at a rate of 2.7% kbar”, much higher than in previous experiments. The experimental situation can be fitted with the triangular-well approximation if we both assume the change with pressure of the conduction band discontinuity AE, and the deepening of a deep impurity level with activation energy of the order 160 meV at zero pressure. [reprint (PDF)]
11.	Delta-doping optimization for high qualityp-type GaN C. Bayram, J.L. Pau, R. McClintock and M. Razeghi Journal of Applied Physics, Vol. 104, No. 8-- October 15, 2008 ...[Visit Journal] Delta-doping is studied in order to achieve high quality p-type GaN. Atomic force microscopy, x-ray diffraction, photoluminescence, and Hall measurements are performed on the samples to optimize the delta-doping characteristics. The effect of annealing on the electrical, optical, and structural quality is also investigated for different delta-doping parameters. Optimized pulsing conditions result in layers with hole concentrations near 10¹⁸ cm⁻³ and superior crystal quality compared to conventional p-GaN. This material improvement is achieved thanks to the reduction in the Mg activation energy and self-compensation effects in delta-doped p-GaN. [reprint (PDF)]
11.	Thermal conductivity tensors of the cladding and active layers of antimonide infrared lasers and detectors Chuanle Zhou, I. Vurgaftman, C. L. Canedy, C. S. Kim, M. Kim, W. W. Bewley, C. D. Merritt, J. Abell, J. R. Meyer, A. Hoang, A. Haddadi, M. Razeghi, and M. Grayson Optical Materials Express. 2013;3(10):1632-1640.-- October 1, 2013 ...[Visit Journal] The in-plane and cross-plane thermal conductivities of the cladding layers and active quantum wells of interband cascade lasers and type-II superlattice infrared detector are measured by the 2-wire 3ω method. The layers investigated include InAs/AlSb superlattice cladding layers, InAs/GaInSb/InAs/AlSb W-active quantum wells, an InAs/GaSb superlattice absorber, an InAs/GaSb/AlSb M-structure, and an AlAsSb digital alloy. The in-plane thermal conductivity of the InAs/AlSb superlattice is 4-5 times higher than the cross-plane value. The isotropic thermal conductivity of the AlAsSb digital alloy matches a theoretical expectation, but it is one order of magnitude lower than the only previously-reported experimental value. [reprint (PDF)]
11.	GaN nanostructured p-i-n photodiodes J.L. Pau, C. Bayram, P. Giedraitis, R. McClintock, and M. Razeghi Applied Physics Letters, Vol. 93, No. 22, p. 221104-1-- December 1, 2008 ...[Visit Journal] We report the fabrication of nanostructured p-i-n photodiodes based on GaN. Each device comprises arrays of ~200 nm diameter and 520 nm tall nanopillars on a 1 µm period, fabricated by e-beam lithography. Strong rectifying behavior was obtained with an average reverse current per nanopillar of 5 fA at −5 V. In contrast to conventional GaN diodes, nanostructured devices reproducibly show ideality factors lower than 2. Enhanced tunneling through sidewall surface states is proposed as the responsible mechanism for this behavior. Under backillumination, the quantum efficiency in nanostructured devices is partly limited by the collection efficiency of holes into the nanopillars. [reprint (PDF)]
11.	EPR Study of Gd around the Ferroelastic Transition Point of Pb3 (PO4)2 M. RAZEGHI and B. HOULIER M. RAZEGHI et al., phys. stat. sol. (b) 89, K135 (1978) -- October 1, 1978 ...[Visit Journal][reprint (PDF)]
11.	Concentration gradient at an InP/GaAs interface determined by Auger analysis on a chemical bevel J. Cazaux; P. Etienne; M. Razeghi J. Cazaux, P. Etienne, M. Razeghi; Concentration gradient at an InP/GaAs interface determined by Auger analysis on a chemical bevel. J. Appl. Phys. 15 May 1986; 59 (10): 3598–3601-- June 15, 1986 ...[Visit Journal] Experimental results of Auger profiles obtained on a chemical bevel of an InP/GaAs structure are reported. A theoretical procedure is established to convert the intensity profile into concentration profiles. It is applied to evaluate the concentration distribution of each species–Ga, In, As, P–independently of each others with a precision of ±5%. It is verified that the composition of the interface is GaxIn1−xAsyP1−y (0≤x, y≤1). Owing to differences between the atomic diffusions of III‐ and V‐type elements, the transition region can be subdivided into three regions having the following compositions: (i) GaAsyP1−y with 0.87≤y≤1; (ii) GaxIn1−xAsyP1−y with 0≤y≤0.87 and 0.24≤x<1; (iii) PGaxIn1−x with x<0.24. The width of each region is also indicated. [reprint (PDF)]
11.	Extended electrical tuning of quantum cascade lasers with digital concatenated gratings S. Slivken, N. Bandyopadhyay, Y. Bai, Q. Y. Lu, and M. Razeghi Appl. Phys. Lett. 103, 231110 (2013)-- December 6, 2013 ...[Visit Journal] In this report, the sampled grating distributed feedback laser architecture is modified with digital concatenated gratings to partially compensate for the wavelength dependence of optical gain in a standard high efficiency quantum cascade laser core. This allows equalization of laser threshold over a wide wavelength range and demonstration of wide electrical tuning. With only two control currents, a full tuning range of 500 nm (236 cm⁻¹) has been demonstrated. Emission is single mode, with a side mode suppression of >20 dB. [reprint (PDF)]
11.	Radiometric characterization of long-wavelength infrared type II strained layer superlattice focal plane array under low-photon irradiance conditions J. Hubbs, V. Nathan, M. Tidrow, and M. Razeghi Optical Engineering, Vol. 51, No. 6, p. 064002-1-- June 15, 2012 ...[Visit Journal] We present the results of the radiometric characterization of an “M” structure long wavelength infrared Type-II strained layer superlattice(SLS) infrared focal plane array (IRFPA) developed by Northwestern University (NWU). The performance of the M-structure SLS IRFPA was radiometrically characterized as a function of photon irradiance, integration time, operating temperature, and detector bias. Its performance is described using standard figures of merit: responsivity, noise, and noise equivalent irradiance. Assuming background limited performance operation at higher irradiances, the detector quantum efficiency for the SLS detector array is approximately 57%. The detector dark density at 80 K is 142 μA∕cm², which represents a factor of seven reduction from previously measured devices. [reprint (PDF)]
11.	Growth and Characterization of Type-II Non-Equilibrium Photovoltaic Detectors for Long Wavelength Infrared Range H. Mohseni, J. Wojkowski, A. Tahraoui, M. Razeghi, G. Brown and W. Mitche SPIE Conference, San Jose, CA, -- January 26, 2000 ...[Visit Journal] Growth and characterization of type-II detectors for mid-IR wavelength range is presented. The device has a p-i-n structure is designed to operate in the non-equilibrium mode with low tunneling current. The active layer is a short period InAs/GaSb superlattice. Wider bandgap p-type AlSb and n-type InAs layers are used to facilitate the extraction of both electronics and holes from the active layer for the first time. The performance of these devices were compared to the performance of devices grown at the same condition, but without the AlSb barrier layers. The processed devices with the AlSb barrier show a peak responsivity of about 1.2 A/W with Johnson noise limited detectivity of 1.1 X 10¹¹ cm·Hz^½/W at 8 μm at 80 K at zero bias. The details of the modeling, growth, and characterizations will be presented. [reprint (PDF)]
11.	High-Performance Type-II InAs/GaSb Superlattice Photodiodes with Cutoff Wavelength Around 7 µm Y. Wei, A. Hood, H. Yau, V. Yazdanpanah, M. Razeghi, M.Z. Tidrow and V. Nathan Applied Physics Letters, 86 (9)-- February 28, 2005 ...[Visit Journal] We report the most recent result in the area of type-II InAs/GaSb superlattice photodiodes that have a cutoff wavelength around 7 µm at 77 K. Superlattice with a period of 40 Å lattice matched to GaSb was realized using Ga_xIn_1–x type interface engineering technique. Compared with significantly longer period superlattices, we have reduced the dark current density under reverse bias dramatically. For a 3 µm thick structure, using sulfide-based passivation, the dark current density reached 2.6×10^–5 A/cm² at –3 V reverse bias at 77 K. At this temperature the photodiodes have R₀A of 9300 Ω·cm² and a thermally limited zero bias detectivity of 1×10¹² cm·Hz^½/W. The 90%–10% cutoff energy width was only 16.5 meV. The devices did not show significant dark current change at 77 K after three months storage in the atmosphere. [reprint (PDF)]
11.	Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers Quanyong Lu, Donghai Wu, Saumya Sengupta, Steven Slivken, Manijeh Razeghi Nature Scientific Reports 6, Article number: 23595-- March 24, 2016 ...[Visit Journal] A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν ~ 1–5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06–4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers. [reprint (PDF)]
11.	Interface roughness scattering in thin, undoped GaInP/GaAs quantum wells W. C. Mitchel, G.J. Brown, I. Lo, S. Elhamri, M. Aboujja, K. Ravindran, R.S. Newrock, M. Razeghi, and X. He Applied Physics Letters 65 (12)-- September 19, 1994 ...[Visit Journal] Electronic transport properties of very thin undoped GaInP/GaAs quantum wells have been measured by temperature dependent low field Hall effect and by Shubnikov–de Haas effect. Strong Shubnikov–de Haas oscillations were observed after increasing the electron concentration via the persistent photocurrent effect. Low temperature mobilities of up to 70 ,000 cm²/V· s at carrier concentrations of 6.5×10¹¹ cm⁻² were observed in a 20 Å quantum well. The results are compared with the theory of interface roughness scattering which indicates extremely smooth interfaces; however, discrepancies between experiment and theory are observed. [reprint (PDF)]
11.	Electrically pumped photonic crystal distributed feedback quantum cascade lasers Y. Bai, P. Sung, S.R. Darvish, W. Zhang, A. Evans, S. Slivken, and M. Razeghi SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 69000A-1-8.-- February 1, 2008 ...[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 50 µm and 100 µm width were fabricated with both PCDFB and Fabry-Perot feedback mechanisms. The Fabry-Perot device has a broad emitting spectrum and a broad far-field character. The PCDFB devices have primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half-maximum of 4.8 degrees and 2.4 degrees for the 50 µm and 100 µm ridge widths, respectively. [reprint (PDF)]
11.	Planar nBn type-II superlattice mid-wavelength infrared photodetectors using zinc ion-implantation Arash Dehzangi, Donghai Wu, Ryan McClintock, Jiakai Li, and Manijeh Razeghi Appl. Phys. Lett. 116, 221103 https://doi.org/10.1063/5.0010273-- June 2, 2020 ...[Visit Journal] In this Letter, we report the demonstration of zinc ion-implantation to realize planar mid-wavelength infrared photodetectors based on type-II InAs/InAs1−xSbx superlattices. At 77 K, the photodetectors exhibit a peak responsivity of 0.68 A/W at 3.35 μm, corresponding to a quantum efficiency of 23.5% under Vb = −80 mV, without anti-reflection coating; these photodetectors have a 100% cutoff wavelength of 4.28 μm. With an R0 × A value of 1.53 × 104 Ω cm2 and a dark current density of 1.23 × 10−6 A/cm2 under an applied bias of −80 mV at 77 K, the photodetectors exhibit a specific detectivity of 9.12 × 1011 cm·Hz1/2/W. [reprint (PDF)]
11.	High performance quantum cascade lasers (~11 μm) operating at high temperature (T>= 425K) A. Tahraoui, A. Matlis, S. Slivken, J. Diaz, and M. Razeghi Applied Physics Letters 78 (4)-- January 22, 2001 ...[Visit Journal] We report record-low threshold current density and high output power for λ ∼ 11 μm Al_0.48In_0.52As/Ga_0.47In_0.53As quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and 7.08 kA/cm² at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K. [reprint (PDF)]
11.	High-performance, continuous-wave quantum-cascade lasers operating up to 85° C at λ ~ 8.8 μm J.S. Yu, S. Slivken, A. Evans, and M. Razeghi Applied Physics A: Materials Science & Processing, Vo. 93, No. 2, p. 405-408-- November 1, 2008 ...[Visit Journal] High-temperature, high-power, and continuous-wave (CW) operation of quantum-cascade lasers with 35 active/injector stages at λ∼8.85 μm above room temperature is achieved without using a buried heterostructure. At this long wavelength, the use of a wider ridge waveguide in an epilayer-down bonding scheme leads to a superior performance of the laser. For a high-reflectivity-coated 21 μm×3 mm laser, the output power of 237 mW and the threshold current density of 1.44 kA·cm^-2 at 298 K under CW mode are obtained with a maximum wall-plug efficiency of 1.7%. Further improvements were observed by using a 4-mm-long cavity. The device exhibits 294 mW of output power at 298 K and it operates at a high temperature, even up to 358 K (85°C). The full widths at half-maximum of the laser beam in CW operation for the parallel and the perpendicular far-field patterns are 25°and 63°, respectively. [reprint (PDF)]
11.	High quality LEO growth and characterization of GaN films on Al₂O₃ and Si substrates M. Razeghi, P. Kung, D. Walker, M. Hamilton, and J. Diaz SPIE International Conference on Solid State Crystals, Zakopane, Poland; Proceedings 3725-- October 12, 1998 ...[Visit Journal] We report the lateral epitaxial overgrowth (LEO) of GaN films on (00.1) Al₂O₃ and (111) Si substrates by metalorganic chemical vapor deposition. The LEO on Si substrates was possible after achieving quasi monocrystalline GaN template films on (111) Si substrates. X-ray diffraction, photoluminescence, scanning electron microscopy and atomic force microscopy were used to assess the quality of the LEO films. Lateral growth rates more than 5 times as high as vertical growth rates were achieved for both LEO growths of GaN on sapphire and silicon substrates. [reprint (PDF)]
11.	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)]
11.	Top-emission ultraviolet light-emitting diodes with peak emission at 280 nm A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, and M. Razeghi Virtual Journal of Nanoscale Science & Technology, 5-- August 5, 2002 ...[Visit Journal][reprint (PDF)]
11.	High-power high-wall plug efficiency mid-infrared quantum cascade lasers based on InP/GaInAs/InAlAs material system M. Razeghi SPIE Proceedings, San Jose, CA Volume 7230-11-- January 26, 2009 ...[Visit Journal] The latest result at the Center for Quantum Devices about high power, high wall plug efficiency, mid-infrared quantum cascade lasers (QCLs) is presented. At an emitting wavelength of 4.8 µm, an output power of 3.4 W and a wall plug efficiency of 16.5% are demonstrated from a single device operating in continuous wave at room temperature. At a longer wavelength of 10.2 µm, average power as high as 2.2 W is demonstrated at room temperature. Gas-source molecular beam epitaxy is used to grow the QCL core in an InP/GaInAs/InAlAs material system. Fe-doped semiinsulating regrowth is performed by metal organic chemical vapor deposition for efficient heat removal and low waveguide loss. This accomplishment marks an important milestone in the development of high performance midinfrared QCLs. [reprint (PDF)]

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