Center for Quantum Devices - Most Downloaded Journal Articles

Page 13 of 30: Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 >> Next (738 Items)

15.	Fabrication of nanostructured heterojunction LEDs using self-forming Moth-Eye Arrays of n-ZnO Nanocones Grown on p-Si (111) by PLD D.J. Rogers; V.E. Sandana; F. Hosseini Teherani; M. Razeghi; H.-J. Drouhin Proc. SPIE 7217, Zinc Oxide Materials and Devices IV, 721708 (February 17, 2009)-- February 17, 2009 ...[Visit Journal] ZnO nanostructures were grown on Si (111) substrates using Pulsed Laser Deposition. The impact of growth temperature (T_s) and Ar pressure (P_Ar) on the morphology, crystal structure and photoluminescence was investigated. Various types of ZnO nanostructures were obtained. Self-forming arrays of vertically-aligned nanorods and nanocones with strong c-axis crystallographic orientation and good optical response were obtained at higher T_s. The nanocone, or "moth-eye" type structures were selected for LED development because of their graded effective refractive index, which could facilitate improved light extraction at the LED/air interface. Such moth-eye arrays were grown on p-type Si (111) substrates to form heteroj unction LEDs with the n-type ZnO nanocones acting as an active component of the device. These nanostructured LEDs gave rectifying I/V characteristics with a threshold voltage of about 6V and a blueish-white electroluminescence, which was clearly visible to the naked eye. [reprint (PDF)]
15.	Evaluation of the Band Offsets of GaAs-GaInP Multilayers by Electroreflectance Razeghi M., D. Yang, J.W. Garland, Z. Zhang, D. Xue SPIE Proceedings, Vol. 1676, pp. 130-- January 1, 1992 ...[Visit Journal] We report the first band offset measurement of GaAs/Ga_0.51In_0.49P multiquantum wells and superlattices by electrolyte electroreflectance spectroscopy. The conduction and valence band discontinuities (Delta) Ec equals 159 ± 4 meV and (Delta) Ev equals 388 ± 6 meV have been measured. The values found for the conduction band, heavy-hole and light-hole masses in the GaInP barriers and GaAs wells and for the split-off well mass are in excellent agreement with the literature. The intraband, intersubband transition energies, which are important for III - V infrared detection devices, also were directly measured. [reprint (PDF)]
15.	Type-II ‘M’ Structure Photodiodes: An Alternative Material Design for Mid-Wave to Long Wavelength Infrared Regimes B-M. Nguyen, M. Razeghi, V. Nathan, and G.J. Brown SPIE Conference, January 25-29, 2007, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices IV, Vol. 6479, p. 64790S-1-10-- January 29, 2007 ...[Visit Journal] In this work, an AlSb-containing Type-II InAs/GaSb superlattice, the so-called M-structure, is presented as a candidate for mid and long wavelength infrared detection devices. The effect of inserting an AlSb barrier in the GaSb layer is discussed and predicts many promising properties relevant to practical use. A good agreement between the theoretical calculation based on Empirical Tight Binding Method framework and experimental results is observed, showing the feasibility of the structure and its properties. A band gap engineering method without material stress constraint is proposed. [reprint (PDF)]
15.	Negative and positive luminescence in mid-wavelength infrared InAs/GaSb superlattice photodiodes D. Hoffman, A. Gin, Y. Wei, A. Hood, F. Fuchs, and M. Razeghi IEEE Journal of Quantum Electronics, 41 (12)-- December 1, 2005 ...[Visit Journal] The quantum efficiency of negative and positive luminescence in binary type-II InAs-GaSb superlattice photodiodes has been investigated in the midinfrared spectral range around the 5-μm wavelength. The negative luminescence efficiency is nearly independent on temperature in the entire range from 220 to 325 K. For infrared diodes with a 2-μm absorbing layer, processed without anti-reflection coating, a negative luminescence efficiency of 45% is found, indicating very efficient minority carrier extraction. The temperature dependent measurements of the quantum efficiency of the positive luminescence enables for the determination of the capture cross section of the Shockley-Read-Hall centers involved in the competing nonradiative recombination. [reprint (PDF)]
15.	First Demonstration of ~ 10 microns FPAs in InAs/GaSb SLS M. Razeghi, P.Y. Delaunay, B.M. Nguyen, A. Hood, D. Hoffman, R. McClintock, Y. Wei, E. Michel, V. Nathan and M. Tidrow IEEE LEOS Newsletter 20 (5)-- October 1, 2006 ...[Visit Journal] The concept of Type-II InAs/GaSb superlattice was first brought by Nobel Laureate L. Esaki, et al. in the 1970s. There had been few studies on this material system until two decades later when reasonable quality material growth was made possible using molecular beam epitaxy. With the addition of cracker cells for the group V sources and optimizations of material growth conditions, the superlattice quality become significantly improved and the detectors made of these superlattice materials can meet the demand in some practical field applications. Especially in the LWIR regime, it provides a very promising alternative to HgCdTe for better material stability and uniformity, etc. We have developed the empirical tight binding model (ETBM) for precise determination of the superlattice bandgap. [reprint (PDF)]
15.	Fabrication of GaN Nanotubular Material using MOCVD with an Aluminium Oxide Membrane W.G. Jung, S.H. Jung, P. Kung, and M. Razeghi Nanotechnology 17-- January 1, 2006 ...[Visit Journal] GaN nanotubular material is fabricated with an aluminium oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminium oxide membrane with ordered nanoholes is used as a template. Gallium nitride is deposited at the inner wall of the nanoholes in the aluminium oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis conditions in MOCVD are obtained successfully for the gallium nitride nanotubular material in this research. The diameter of the GaN nanotube fabricated is approximately 200–250 nm and the wall thickness is about 40–50 nm. [reprint (PDF)]
15.	Very high quality p-type Al_xGa_1-xN/GaN superlattice A. Yasan and M. Razeghi special ISDRS issue of Solid State Electronics Journal, 47-- January 1, 2003 ...[Visit Journal] Very high quality p-type Al_xGa_1−xN/GaN superlattice has been achieved through optimization of Mg flow and period of superlattice. Theoretical model was used to optimize the structure of superlattice by choosing suitable Al compositions and superlattice periods. The experiments show that for x=0.26, the resistivity is as low as 0.19 Ω cm and hole concentration is as high as 4.2×10¹⁸ cm⁻³, the highest values ever reported for p-type AlGaN/GaN superlattices. Hall effect measurement and admittance spectroscopy on the samples confirm the high quality of the superlattices. The activation energy calculated for p-type GaN and p-type A_0.1Ga_0.9N/GaN superlattice is estimated to be not, vert, similar 125 and 3 meV respectively. [reprint (PDF)]
15.	High peak power 16 m InP-related quantum cascade laser A. Szerlinga,∗, S. Slivkenb, M. RazeghibaInstytut Opto-Electronics Review 25, pp. 205–208-- July 22, 2017 ...[Visit Journal] tIn this paper ∼16 μm-emitting multimode InP-related quantum cascade lasers are presented with themaximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricatedand characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window ontop of the ridge, and the lasers with the SiO₂layer removed from the metal-free window area. Dual-wavelength operation was obtained, at ∼15.6 μm (641 cm⁻¹) and at ∼16.6 μm (602 cm⁻¹) for laserswith SiO₂-removed, while within the emission spectrum of the lasers with SiO₂-left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ∼15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge. [reprint (PDF)]
15.	Low-Threshold 7.3 μm Quantum Cascade Lasers Grown by Gas-Source Molecular Beam Epitaxy S. Slivken, A. Matlis, A. Rybaltowski, Z. Wu and M. Razeghi Applied Physics Letters 74 (19)-- May 19, 1999 ...[Visit Journal] We report low-threshold 7.3 μm superlattice-based quantum cascade lasers. The threshold current density is 3.4 kA/cm² at 300 K and 1.25 kA/cm² at 79 K in pulsed mode for narrow (∼20 μm), 2 mm-long laser diodes. The characteristic temperature (T₀) is 210 K. The slope efficiencies are 153 and 650 mW/A at 300 and 100 K, respectively. Power output is in excess of 100 mW at 300 K. Laser far-field intensity measurements give divergence angles of 64° and 29° in the growth direction and in the plane of the quantum wells, respectively. Far-field simulations show excellent agreement with the measured results. [reprint (PDF)]
15.	Low pressure metalorganic chemical vapor deposition of high quality AlN and GaN thin films on sapphire and silicon substrates P. Kung, X. Zhang, E. Bigan, and M. Razeghi Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal] High quality AlN and GaN epilayers have been grown on basal plane sapphire by low pressure metalorganic chemical vapor deposition. The X-ray rocking curve linewidth of the AlN and GaN films were about 100 and 30 arcsecs respectively. Sharp absorption edges were determined at 6.1 and 3.4 eV respectively. Successful donor-bound excitonic luminescence emissions were detected for GaN films grown on sapphire and silicon. Two additional lines at 3.37 and 3.31 eV were observed on GaN on sapphire and assumed to be impurity-related. Doping of GaN layers was achieved with magnesium. Mg-related photoluminescence emissions were successfully detected on as-grown samples, without any post-growth treatment. [reprint (PDF)]
15.	High performance terahertz quantum cascade laser sources based on intracavity difference frequency generation Q.Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi Optics Express, Vol. 21, No. 1, p. 968-- January 14, 2013 ...[Visit Journal] We demonstrate high power, room temperature, single-mode THz emissions based on intracavity difference frequency generation from mid-infrared quantum cascade lasers. Dual active regions both featuring giant nonlinear susceptibilities are used to enhance the THz power and conversion efficiency. The THz frequency is lithographically tuned by integrated dual-period distributed feedback gratings with different grating periods. Single mode emissions from 3.3 to 4.6 THz with side-mode suppression ratio and output power up to 40 dB and 65 µW are obtained, with a narrow linewidth of 5 GHz. [reprint (PDF)]
15.	Review of high power frequency comb sources based on InP From MIR to THZ at CQD Manijeh Razeghi, Quanyong Lu, Donghai Wu, Steven Slivken Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States-- September 14, 2018 ...[Visit Journal] We present the recent development of high performance compact frequency comb sources based on mid-infrared quantum cascade lasers. Significant performance improvements of our frequency combs with respect to the continuous wave power output, spectral bandwidth, and beatnote linewidth are achieved by systematic optimization of the device's active region, group velocity dispersion, and waveguide design. To date, we have demonstrated the most efficient, high power frequency comb operation from a free-running room temperature continuous wave (RT CW) dispersion engineered QCL at λ~5-9 μm. In terms of bandwidth, the comb covered a broad spectral range of 120 cm⁻¹ with a radio-frequency intermode beatnote spectral linewidth of 40 Hz and a total power output of 880 mW at 8 μm and 1 W at ~5.0 μm. The developing characteristics show the potential for fast detection of various gas molecules. Furthermore, THz comb sources based on difference frequency generation in a mid-IR QCL combs could be potentially developed. [reprint (PDF)]
15.	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)]
15.	TEG IN LP-MO CVD Ga 0 4 7 ln 0 S3 As-lnP SUPERLATTICE M. RAZEGHIM. A. POISSONJ. P. LARIVAINB. de CREMOUXJ. P. DUCHEMIN ELECTRONICS LETTERs, 1982 ,Vol. 18-- April 15, 1982 ...[Visit Journal] We report the first successful growth of Ga o .4. 7 In 0 . J3 As-InPsuperlattice by the low-pressure metalorganic chemicalvapour deposition technique, and evidence for TEG proper-ties in these structures. [reprint (PDF)]
15.	Growth and Optimization of GaInAsP/InP Material System for Quantum Well Infrared Photodetector Applications M. Erdtmann, J. Jiang, A. Matlis, A. Tahraoui, C. Jelen, M. Razeghi, and G. Brown SPIE Conference, San Jose, CA, -- January 26, 2000 ...[Visit Journal] Multi-quantum well structures of Ga_xIn_1-xAs_yP_1-y were grown by metalorganic chemical vapor deposition for the fabrication of quantum well IR photodetectors. The thickness and composition of the wells was determined by high-resolution x-ray diffraction and photoluminescence experiments. The intersubband absorption spectrum of the Ga_0.47In_0.53As/InP, Ga_0.38In_0.62As_0.80P_0.20 (1.55 μm)/InP, and Ga_0.27In_0.73As_0.57P_0.43 (1.3 μm))/InP quantum wells are found to have cutoff wavelengths of 9.3 μm, 10.7 micrometers , and 14.2 μm respectively. These wavelengths are consistent with a conduction band offset to bandgap ratio of approximately 0.32. Facet coupled illumination responsivity and detectivity are reported for each composition. [reprint (PDF)]
15.	AlGaN ultraviolet photoconductors grown on sapphire D. Walker, X. Zhang, P. Kung, A. Saxler, S. Javadpour, J. Xu, and M. Razeghi Applied Physics Letters 68 (15)-- April 8, 1996 ...[Visit Journal] Al_xGa_1−xN (0≤x≤0.50) ultraviolet photoconductors with a minimum cutoff wavelength shorter than 260 nm have been fabricated and characterized. The AlGaN active layers were grown on (00⋅1) sapphire substrates by metalorganic chemical vapor deposition (MOCVD). The spectral responsivity of the GaN detector at 360 nm is about 1 A/W biased at 8 V at room temperature. The carrier lifetime derived from the voltage‐dependent responsivity is 0.13–0.36 ms. [reprint (PDF)]
15.	Hole-initiated multiplication in back-illuminated GaN avalanche photodiodes R. McClintock, J.L. Pau, K. Minder, C. Bayram, P. Kung and M. Razeghi Applied Physics Letters, Vol. 90 No. 14, p. 141112-1-- April 2, 2007 ...[Visit Journal] Avalanche p-i-n photodiodes were fabricated on AlN templates for back illumination. Structures with different intrinsic layer thicknesses were tested. A critical electric field of 2.73 MV/cm was estimated from the variation of the breakdown voltage with thickness. From the device response under back and front illumination and the consequent selective injection of holes and electrons in the junction, ionization coefficients were obtained for GaN. The hole ionization coefficient was found to be higher than the electron ionization coefficient as predicted by theory. Excess multiplication noise factors were also calculated for back and front illumination, and indicated a higher noise contribution for electron injection. [reprint (PDF)]
15.	Optimized structure for InGaAsP/GaAs 808nm high power lasers H. Yi, J. Diaz, L.J. Wang, I. Eliashevich, S. Kim, R. Williams, M. Erdtmann, X. He, E. Kolev and M. Razeghi Applied Physics Letters 66 (24)-- June 12, 1995 ...[Visit Journal] The optimized structure for the InGaAsP/GaAs quaternary material lasers (λ=0.808 μm) is investigated for the most efficient high‐power operation through an experiment and theoretical study. A comparative study is performed of threshold current density J_th and differential efficiency η_d dependence on cavity length (L) for two different laser structures with different active layer thickness (150 and 300 Å) as well as for laser structures with different multiple quantum well structures. A theoretical model with a more accurate formulation for minority leakage phenomenon provides explanation for the experimental results and sets general optimization rules for other lasers with similar restrictions on the band gap and refractive index difference between the active layer and the cladding layers. [reprint (PDF)]
15.	EPR Investigations of a Structural Phase Change in Lead Phosphate M. RAZEG M. RAZEGHI: EPR Investigations of a Structural Phase Change, phys. stat. sol. (b) 108, 175 (1981)-- April 10, 2010 ...[Visit Journal] The temperature dependence of the EPR line width of the Mn2+ and Gd3+ in Pb,(PO,), is investigated from -270 to 500 "C. At the first-order ferroelastic transition point (180 "C), an abrupt change in the fine-structure splitting as well as in the resonance line width is observed. Various contributions to fine structure D and E parameters of Mn2+ and Gd3+ are computed, using a point-multipole model. For temperatures near to Tc the correlation time of the fluctuations is estimated to be greater than Die Temperaturabhangigkeit der EPR-Linienbreite von Mn2+,'und Gd3+ in Pb,(PO,), wird zwischen -270 und 500 "C untersucht. Am ferroelastischen vbergangspunkt erster Ordnung (180 "C) wird eine abrupte Anderung der Feinstrukturaufspaltung sowie der Linienbreite der Resonanzlinien beobachtet. Verschiedene Beitrage zu den Feinstrukturparametern D und E von Mn2+ und Gd3+ werden mittels eines Punkt-Multipol-Modells berechnet. Fur Temperaturen in der Nahe von T, wird die Korrelationszeit der Fluktuationen eu groI3er als s. s bestimmt. [reprint (PDF)]
15.	Development of Quantum Cascade Lasers for High Peak Output Power and Low Threshold Current Density S. Slivken and M. Razeghi Solid State Electronics 46-- January 1, 2002 ...[Visit Journal] Design and material optimization are used to both decrease the threshold current density and increase the output power for quantum cascade lasers. Waveguides are designed to try and minimize free-carrier and surface-plasmon absorption. Excellent material characterization is also presented, showing excellent control over layer thickness, interface quality, and doping level. Experiments are done to both optimize the injector doping level and to maximize the output power from a single aperture. At 300 K, a threshold current density as low as 1.8 kA/cm² is reported, along with peak powers of approximately 2.5 W. Strain-balanced lasers are also demonstrated at λnot, vert, similar5 μm, exhibiting threshold current densities<300 A/cm² at 80 K. These values represent the state-of-the-art for mid-infrared lasers with λ>4 μm [reprint (PDF)]
15.	Dark current reduction in microjunction-based double electron barrier type-II InAs/InAsSb superlattice long-wavelength infrared photodetectors Romain Chevallier, Abbas Haddadi, & Manijeh Razeghi Scientific Reports 7, Article number: 12617-- October 3, 2017 ...[Visit Journal] Microjunction InAs/InAsSb type-II superlattice-based long-wavelength infrared photodetectors with reduced dark current density were demonstrated. A double electron barrier design was employed to reduce both bulk and surface dark currents. The photodetectors exhibited low surface leakage after passivation with SiO2, allowing the use of very small size features without degradation of the dark current. Fabricating microjunction photodetectors (25 × 25 µm² diodes with 10 × 10 µm² microjunctions) in combination with the double electron barrier design results in a dark current density of 6.3 × 10⁻⁶ A/cm² at 77 K. The device has an 8 µm cut-off wavelength at 77 K and exhibits a quantum efficiency of 31% for a 2 µm-thick absorption region, which results in a specific detectivity value of 1.2 × 10¹² cm·Hz^½/W. [reprint (PDF)]
15.	Comparison of Gain and Threshold Current Density for InGaAsP/GaAs λ = 808 nm) Lasers with Different Quantum-Well Thickness H.J. Yi, J. Diaz, I. Eliashevich, G. Lukas, S. Kim, D. Wu, M. Erdtmann, C. Jelen, S. Slivken, L.J. Wang, and M. Razeghi Journal of Applied Physics 79 (11)-- July 1, 1996 ...[Visit Journal] We investigated the quantum‐size effects of quantum well (QW) on gain and threshold current density for InGaAsP/GaAs (λ=808 nm) laser diodes. In this work, a comparison is made of lasers with different QW thickness while keeping the optical confinement factors constant. We found that the threshold current density and differential efficiency were not affected by narrowing the QW thickness. The theoretical model taking into account the mixing of the valence bands and momentum relaxation for InGaAsP/GaAs lasers with spontaneous emission (optically pumped) measurement shows that the absence of difference between these structures can be attributed to the high relaxation rate. [reprint (PDF)]
15.	High-performance InAs quantum-dot infrared photodetectors grown on InP substrate operating at room temperature H. Lim, S. Tsao, W. Zhang, and M. Razeghi Applied Physics Letters, Vol. 90, No. 13, p. 131112-1-- March 26, 2007 ...[Visit Journal] The authors report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metal-organic chemical vapor deposition. The detectivity was 2.8×10¹¹ cm·Hz^1/2/W at 120 K and a bias of −5 V with a peak detection wavelength around 4.1 μm and a quantum efficiency of 35%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature, which gives a detectivity of 6.7×10⁷ cm·Hz^1/2/W. [reprint (PDF)]
15.	High speed type-II superlattice based photodetectors transferred on sapphire Arash Dehzangi, Ryan McClintock, Donghai Wu, Jiakai Li, Stephen Johnson, Emily Dial and Manijeh Razeghi Applied Physics Express, Volume 12, Number 11-- October 3, 2019 ...[Visit Journal] We report the substrate transfer of InAs/GaSb/AlSb based type-II superlattice (T2SL) e-SWIR photodetector from native GaSb substrates to low loss sapphire substrate in order to enhance the frequency response of the device. We have demonstrated the damage-free transfer of T2SL-based thin-films to sapphire substrate using top–down processing and a chemical epilayer release technique. After transfer the −3 dB cut-off frequency increased from 6.4 GHz to 17.2 GHz, for 8 μm diameter circular mesas under -15 V applied bias. We also investigated the cut-off frequency verses applied bias and lateral scaling to assess the limitations for even higher frequency performance. Direct Link [reprint (PDF)]
15.	Investigation of MgZnO/ZnO heterostructures grown on c-sapphire substrates by pulsed laser deposition D. J. Rogers ; F. Hosseini Teherani ; P. Bove ; A. Lusson ; M. Razeghi Proc. SPIE 8626, Oxide-based Materials and Devices IV, 86261X (March 18, 2013)-- March 18, 2013 ...[Visit Journal] MgZnO thin films were grown on c-sapphire and ZnO-coated c-sapphire substrates by pulsed laser deposition from a ZnMgO target with 4 at% Mg. The MgZnO grown on the ZnO underlayer showed significantly better crystal quality than that grown directly on sapphire. AFM studies revealed a significant deterioration in surface morphology for the MgZnO layers compared with the ZnO underlayer. Optical transmission studies indicated a MgZnO bandgap of 3.61eV (compared with 3.34eV for the ZnO), which corresponds to a Mg content of about 16.1 at%. The MgZnO/ZnO heterojunction showed an anomalously low resistivity, which was more than two orders of magnitude less than the MgZnO layer and an order of magnitude lower than that for the ZnO layer. It was suggested that this may be attributable to the presence of a 2D electron gas at the ZnMgO/ZnO heterointerface. [reprint (PDF)]

Page 13 of 30: Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 >> Next (738 Items)