Center for Quantum Devices - Most Downloaded Journal Articles

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14.	Radiative recombination of confined electrons at the MgZnO/ ZnO heterojunction interface Sumin Choi, David J. Rogers, Eric V. Sandana, Philippe Bove, Ferechteh H. Teherani, Christian Nenstiel, Axel Hoffmann, Ryan McClintock, Manijeh Razeghi, David Look, Angus Gentle, Matthew R. Phillips & Cuong Ton-That Nature Scientific Reports 7, pp. 7457-- August 7, 2017 ...[Visit Journal] We investigate the optical signature of the interface in a single MgZnO/ZnO heterojunction, which exhibits two orders of magnitude lower resistivity and 10 times higher electron mobility compared with the MgZnO/Al₂O₃ film grown under the same conditions. These impressive transport properties are attributed to increased mobility of electrons at the MgZnO/ZnO heterojunction interface. Depthresolved cathodoluminescence and photoluminescence studies reveal a 3.2 eV H-band optical emission from the heterointerface, which exhibits excitonic properties and a localization energy of 19.6 meV. The emission is attributed to band-bending due to the polarization discontinuity at the interface, which leads to formation of a triangular quantum well and localized excitons by electrostatic coupling. [reprint (PDF)]
14.	Demonstration of mid-wavelength infrared nBn photodetectors based on type-II InAs/InAs_1-xSb_x superlattice grown by metal-organic chemical vapor deposition Donghai Wu, Arash Dehzangi, and Manijeh Razeghi Appl. Phys. Lett. 115, 061102-- August 6, 2019 ...[Visit Journal] We report design, growth, and characterization of midwavelength infrared nBn photodetectors based on a type-II InAs/InAs_1-xSb_x superlattice on a GaSb substrate grown by metal-organic chemical vapor deposition. An InAs/AlAs_1-ySb_y/InAs/InAs_1-xSb_x superlattice design was used as the large bandgap electron barrier in the photodetectors. At 150 K, the photodetector exhibits a peak responsivity of 1.23 A/W, corresponding to a quantum efficiency of 41% at an applied bias voltage of −100 mV under front-side illumination, with a 50% cut-off wavelength of 4.6 μm. With an R × A of 356 Ω·cm² and a dark current density of 1.6 × 10⁻⁴ A/cm² under an applied bias of −100 mV at 150 K, the photodetector exhibits a specific detectivity of 1.4 × 10¹¹ cm·Hz^1/2/W. [reprint (PDF)]
14.	III-Nitride Optoelectronic Devices: From ultraviolet detectors and visible emitters towards terahertz intersubband devices M. Razeghi, C. Bayram, Z. Vashaei, E. Cicek and R. McClintock IEEE Photonics Society 23rd Annual Meeting, November 7-10, 2010, Denver, CO, Proceedings, p. 351-352-- January 20, 2011 ...[Visit Journal] III-nitride optoelectronic devices are discussed. Ultraviolet detectors and visible emitters towards terahertz intersubband devices are reported. Demonstration of single photon detection efficiencies of 33% in the ultraviolet regime, intersubband energy level as low as in the mid-infrared regime, and GaN-based resonant tunneling diodes with negative resistance of 67 Ω are demonstrated. [reprint (PDF)]
14.	Scaling in back-illuminated GaN avalanche photodiodes K. Minder, J.L. Pau, R. McClintock, P. Kung, C. Bayram, M. Razeghi and D. Silversmith Applied Physics Letters, Vol. 91, No. 7, p. 073513-1-- August 13, 2007 ...[Visit Journal] Avalanche p-i-n photodiodes of various mesa areas were fabricated on AlN templates for back illumination for enhanced performance through hole-initiated multiplication, and the effects of increased area on device performance were studied. Avalanche multiplication was observed in mesa sizes up to 14,063 µm^2 under linear mode operation. Uniform gain and a linear increase of the dark current with area were demonstrated. [reprint (PDF)]
14.	Photovoltaic MWIR type-II superlattice focal plane array on GaAs substrate E.K. Huang, P.Y. Delaunay, B.M. Nguyen, S. Abdoullahi-Pour, and M. Razeghi IEEE Journal of Quantum Electronics (JQE), Vol. 46, No. 12, p. 1704-1708-- December 1, 2010 ...[Visit Journal] Recent improvements in the performance of Type-II superlattice (T2SL) photodetectors has spurred interest in developing low cost and large format focal plane arrays (FPA) on this material system. Due to the limitations of size and cost of native GaSb substrates, GaAs is an attractive alternative with 8” wafers commercially available, but is 7.8% lattice mismatched to T2SL. In this paper, we present a photovoltaic T2SL 320 x 256 focal plane array (FPA) in the MWIR on GaAs substrate. The FPA attained a median noise equivalent temperature difference (NEDT) of 13 mK and 10mK (F#=2.3) with integration times of 10.02 ms and 19.06 ms respectively at 67 K. [reprint (PDF)]
14.	Hybrid green LEDs with n-type ZnO substituted for N-type GaN in an inverted P-N junction F. Hosseini Teherani; M. Razeghi; D.J. Rogers; Can Bayram; R. McClintock LEOS Annual Meeting Conference Proceedings, LEOS '09. IEEE, [5343231] (2009) -- October 4, 2009 ...[Visit Journal] Recently, the GaN and ZnO materials systems have attracted considerable attention because of their use in a broad range of emerging applications including light-emitting diodes (LEDs) and solar cells. GaN and ZnO are similar materials with direct wide bandgaps, wurtzite crystal structure, high thermal stability and comparable thermal expansion coefficients, which makes them well suited for heterojunction fabrication. Two important advantages of GaN over ZnO are the reliable p-type doping and the mature know-how for bandgap engineering. Thus GaN-based LEDs can be made to emit from the deep UV right into the green through alloying with Al and In, respectively. The performance is not identical at all wavelengths, however, and the performance of InGaN-based green LEDs is still relatively poor. [reprint (PDF)]
14.	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)]
14.	Band edge tunability of M-structure for heterojunction design in Sb based Type-II superlattice photodiodes B.M. Nguyen, D. Hoffman, P.Y. Delaunay, E.K. Huang, M. Razeghi, and J. Pellegrino Applied Physics Letters, Vol. 93, No. 16, p. 163502-1-- October 20, 2008 ...[Visit Journal] We present theoretically and experimentally the effect of the band discontinuity in Type-II misaligned InAs/GaSb superlattice heterodiodes. Calculations using the empirical tight binding method have shown the great flexibility in tuning the energy levels of the band edge in M-structure superlattice as compared to the standard InAs/GaSb superlattice. Through the experimental realization of several p-pi-M-n photodiodes, the band discontinuity alignment between the standard binary-binary superlattice and the M-structured superlattice was investigated via optical characterization. The agreement between the theoretical predictions and the experimental measurement confirms the capability of controlling the M-structure band edges and suggests a way to exploit this advantage for the realization of heterostructures containing an M-structured superlattice without bias dependent operation. [reprint (PDF)]
14.	ZnO 3D flower-like nanostructure synthesized on GaN epitaxial layer by simple route hydrothermal process J.M. Jung, C.R. Kim, H. Ryu, M. Razeghi and W.G. Jung Journal of Alloys and Compounds-- September 15, 2007 ...[Visit Journal] The 3D type, flower-like ZnO nanostructures from particle to flower-like or chestnut bur are fabricated on the GaN epitaxial layer substrate through the simple-route hydrothermal process. Structural characterization was made for the ZnO 3D nanostructures synthesized in different pH ranging from 9.5 to 11.0. The growth model was proposed and discussed regarding the fabrication mechanism and morphology of ZnO 3D flower-like nanostructure. The flower-like ZnO is composed of many thin single crystals ZnO nanorods. Bigger and thicker ZnO structure is fabricated with the increase of pH in solution. The enhanced UV emission in the PL measurement and the spectra in the Raman spectroscopy for ZnO–GaN heterojunction material were discussed. [reprint (PDF)]
14.	High Quantum Efficiency Solar-Blind Photodetectors R. McClintock, A. Yasan, K. Mayes, D. Shiell, S. Darvish, P. Kung and M. Razeghi SPIE Conference, Jose, CA, Vol. 5359, pp. 434-- January 25, 2004 ...[Visit Journal] We report AlGaN-based back-illuminated solar-blind p-i-n photodetectors with a record peak responsivity of 150 mA/W at 280 nm, corresponding to a high external quantum efficiency of 68%, increasing to 74% under 5 volts reverse bias. Through optimization of the p-AlGaN layer, we were able to remove the out-of-band negative photoresponse originating from the Schottky-like p-type metal contact, and hence significantly improve the degree of solar-blindness [reprint (PDF)]
14.	Monolithic integration of a short‐length GaInAs photoconductor with a GaAs/GaAlAs optical waveguide on a GaAs semi‐insulating substrate F. Mallecot; J. F. Vinchant; M. Razeghi; D. Vandermoere; J. P. Vilcot; D. Decoster Appl. Phys. Lett. 53, 2522–2524 (1988)-- December 19, 1988 ...[Visit Journal] We report the first fabrication of a GaO. 47 Inn. 53 As planar photoconductive detector, associated with a GaAs/GaAIAs rib waveguide grown on a semi-insulating GaAs substrate, which needs a short-length absorbing layer to detect the optical signal. Because of the GaAIAs epilayer, a GalnAs length of about 100 tl1n only is needed to detect 90% of the opticai signal, accordingly to results predicted using a four-layer model with complex refractive indices in each layer. [reprint (PDF)]
14.	Infrared Imaging Arrays Using Advanced III-V Materials and technology M. Razeghi, J.D. Kim, C. Jelen, S. Slivken, E. Michel, H. Mohseni, J.J. Lee, J. Wojkowski, K.S. Kim, H.I. Jeon, and J. X IEEE Proceedings, Advanced Workshop on Frontiers in Electronics (WOFE), Tenerife, Spain;-- January 6, 1997 ...[Visit Journal] Photodetectors operating in the 3-5 and 8-12 μm atmospheric windows are of great importance for applications in infrared (IR) thermal imaging. HgCdTe has been the dominant material system for these applications. However, it suffers from instability and non-uniformity problems over large areas due to high Hg vapor pressure during the material, growth. There has been a lot of interest in the use of heteroepitaxially grown Sb-based alloys, its strained layer superlattices, and GaAs based quantum wells as alternatives to MCT. This interest has been driven by the advanced material growth and processing technology available for the III-V material system [reprint (PDF)]
14.	Comprehensive study of blue and green multi-quantum-well light-emitting diodes grown on conventional and lateral epitaxial overgrowth GaN C. Bayram, J.L. Pau, R. McClintock and M. Razeghi Applied Physics B: Lasers and Optics, Vol. 95, p. 307-314-- November 29, 2008 ...[Visit Journal] Growths of blue and green multi-quantum wells (MQWs) and light-emitting diodes (LEDs) are realized on lateral epitaxial overgrowth (LEO) GaN, and compared with identical structures grown on conventional GaN. Atomic force microscopy is used to confirm the significant reduction of dislocations in the wing region of our LEO samples before active-region growth. Differences between surface morphologies of blue and green MQWs are analyzed. These MQWs are integrated into LEDs. All devices show a blue shift in the electroluminescence (EL) peak and narrowing in EL spectra with increasing injection current, both characteristics attributed to the band-gap renormalization. Green LEDs show a larger EL peak shift and a broader EL spectrum due to larger piezoelectric field and more indium segregation in the MQWs, respectively. Blue LEDs on LEO GaN show a higher performance than those on conventional GaN; however, no performance difference is observed for green LEDs on LEO GaN versus conventional GaN. The performance of the green LEDs is shown to be primarily limited by the active layer growth quality. [reprint (PDF)]
14.	Demonstration of negative differential resistance in GaN/AlN resonant tunneling didoes at room temperature Z. Vashaei, C. Bayram and M. Razeghi Journal of Applied Physics, Vol. 107, No. 8, p. 083505-- April 15, 2010 ...[Visit Journal] GaN/AlN resonant tunneling diodes (RTD) were grown by metal-organic chemical vapor deposition (MOCVD) and negative differential resistance with peak-to-valley ratios as high as 2.15 at room temperature was demonstrated. Effect of material quality on RTDs’ performance was investigated by growing RTD structures on AlN, GaN, and lateral epitaxial overgrowth GaN templates. Our results reveal that negative differential resistance characteristics of RTDs are very sensitive to material quality (such as surface roughness) and MOCVD is a suitable technique for III-nitride-based quantum devices. [reprint (PDF)]
14.	Room temperature operation of 8-12 μm InSbBi infrared photodetectors on GaAs substrates J.J. Lee, J.D. Kim, and M. Razeghi Applied Physics Letters 73 (5)-- August 3, 1998 ...[Visit Journal] We report the room temperature operation of 8–12 μm InSbBi long-wavelength infrared photodetectors. The InSbBi/InSb heterostructures were grown on semi-insulating GaAs (001) substrates by low pressure metalorganic chemical vapor deposition. The voltage responsivity at 10.6 μm was about 1.9 mV/W at room temperature and the corresponding Johnson noise limited detectivity was estimated to be about 1.2×10⁶ cm·Hz^½/W. The carrier lifetime derived from the voltage dependent responsivity measurements was about 0.7 ns. [reprint (PDF)]
14.	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)]
14.	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)]
14.	InGaAs/InGaP Quantum-Dot Photodetector with a High Detectivity H. Lim, S. Tsao, M. Taguchi, W. Zhang, A. Quivy and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270N-- January 23, 2006 ...[Visit Journal] Quantum-dot infrared photodetectors (QDIPs) have recently been considered as strong candidates for numerous applications such as night vision, space communication, gas analysis and medical diagnosis involving middle and long wavelength infrared (MWIR and LWIR respectively) operation. This is due to their unique properties arising from their 3-dimensional confinement potential that provides a discrete density of states. They are expected to outperform quantum-well infrared photodetectors (QWIPs) as a consequence of their natural sensitivity to normal incident radiation, their higher responsivity and their higher-temperature operation. So far, most of the QDIPs reported in the literature were based on the InAs/GaAs system and were grown by molecular beam epitaxy (MBE). Here, we report on the growth of a high detectivity InGaAs/InGaP QDIP grown on a GaAs substrate using low-pressure metalorganic chemical vapor deposition (MOCVD). [reprint (PDF)]
14.	Investigations on the substrate dependence of the properties in nominally-undoped β-Ga2O3 thin films grown by PLD F. H. Teherani ; D. J. Rogers ; V. E. Sandana ; P. Bove ; C. Ton-That ; L. L. C. Lem ; E. Chikoidze ; M. Neumann-Spallart ; Y. Dumont ; T. Huynh ; M. R. Phillips ; P. Chapon ; R. McClintock ; M. Razeghi Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 101051R-OLD-- March 23, 2017 ...[Visit Journal] Nominally-undoped Ga₂O₃ layers were deposited on a-, c- and r-plane sapphire substrates using pulsed laser deposition. Conventional x-ray diffraction analysis for films grown on a- and c-plane sapphire showed the layers to be in the β-Ga₂O₃ phase with preferential orientation of the (-201) axis along the growth direction. Pole figures revealed the film grown on r-plane sapphire to also be in the β-Ga₂O₃ phase but with epitaxial offsets of 29.5°, 38.5° and 64° from the growth direction for the (-201) axis. Optical transmission spectroscopy indicated that the bandgap was ~5.2eV, for all the layers and that the transparency was > 80% in the visible wavelength range. Four point collinear resistivity and Van der Pauw based Hall measurements revealed the β-Ga₂O₃ layer on r-plane sapphire to be 4 orders of magnitude more conducting than layers grown on a- and c-plane sapphire under similar conditions. The absolute values of conductivity, carrier mobility and carrier concentration for the β-Ga₂O₃ layer on r-sapphire (at 20Ω-1.cm^-1, 6 cm²/Vs and 1.7 x 10¹⁹ cm^-3, respectively) all exceeded values found in the literature for nominally-undoped β-Ga₂O₃ thin films by at least an order of magnitude. Gas discharge optical emission spectroscopy compositional depth profiling for common shallow donor impurities (Cl, F, Si and Sn) did not indicate any discernable increase in their concentrations compared to background levels in the sapphire substrate. It is proposed that the fundamentally anisotropic conductivity in β-Ga₂O₃ combined with the epitaxial offset of the (-201) axis observed for the layer grown on r-plane sapphire may explain the much larger carrier concentration, electrical conductivity and mobility compared with layers having the (-201) axis aligned along the growth direction. [reprint (PDF)]
14.	Demonstration of high performance bias-selectable dual-band short-/mid-wavelength infrared photodetectors based on type-II InAs/GaSb/AlSb superlattices A.M. Hoang, G. Chen, A. Haddadi and M. Razeghi Applied Physics Letters, Vol. 102, No. 1, p. 011108-1-- January 7, 2013 ...[Visit Journal] High performance bias-selectable dual-band short-/mid-wavelength infrared photodetector based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm and 4 μm was demonstrated. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0 × 10⁻⁹ A/cm² at −50 mV bias voltage, providing an associated shot noise detectivity of 3.0 × 10¹³ Jones. The mid-wavelength channel exhibited a quantum efficiency of 33% and a dark current density of 2.6 × 10⁻⁵ A/cm² at 300 mV bias voltage, resulting in a detectivity of 4.0 × 10¹¹ Jones. The spectral cross-talk between the two channels was also discussed for further optimization. [reprint (PDF)]
14.	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)]
14.	Overview of Quantum Cascade Laser Research at the Center for Quantum Devices S. Slivken, A. Evans, J. Nguyen, Y. Bai, P. Sung, S.R. Darvish, W. Zhang and M. Razeghi SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 69000B-1-8.-- February 1, 2008 ...[Visit Journal] Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. In the past year alone, the efficiency and power of our short wavelength lasers (~4.8 µm) has doubled. In continuous wave at room temperature, we have now separately demonstrated ~10% wallplug efficiency and ~700 mW of output power. Up to now, we have been able to show that room temperature continuous wave operation with > 100 mW output power in the 3.8 < λ < 11.5 µm wavelength range is possible. [reprint (PDF)]
14.	High-Performance Focal Plane Arrays Based on InAs-GaSb Superlattices with a 10-micron Cutoff Wavelegth P.Y. Delaunay, B.M. Nguyen, D. Hoffman and M. Razeghi IEEE Journal of Quantum Electronics, Vol. 44, No. 5, p. 462-467-- May 1, 2008 ...[Visit Journal] We report on the demonstration of a focal plane array based on Type-II InAs/GaSb superlattices grown on N-type GaSb substrate with a 50%-cutoff wavelength at 10 μm. The surface leakage occurring after flip-chip bonding and underfill in the Type-II devices was suppressed using a double heterostructure design. The R₀A of diodes passivated with SiO₂ was 23 Ω·cm² after underfill. A focal plane array hybridized to an Indigo readout integrated circuit demonstrated a noise equivalent temperature difference of 33 mK at 81 K, with an integration time of 0.23 ms. [reprint (PDF)]
14.	Optical Investigations of GaAs-GaInP Quantum Wells and Superlattices Grown by Metalorganic Chemical Vapor Deposition Omnes F., and Razeghi M. Applied Physics Letters 59 (9), p. 1034-- May 28, 1991 ...[Visit Journal] Recent experimental results on the photoluminescence and photoluminescence excitation of GaAs‐Ga_0.51In_0.49P lattice‐matched quantum wells and superlattices are discussed. The full width at half maximum of a 10‐period GaAs‐GaInP superlattice with Lz=90 Å and LB=100 Å is 4 meV at 4 K. The photoluminescence excitation exhibits very sharp peaks attributed to the electron to light‐hole and electron to heavy‐hole transitions. The GaInP‐GaAs interface suffers from memory effect of In, rather than P or As elements. [reprint (PDF)]
14.	Solar-Blind Al_xGa_1-xN p-i-n Photodetectors grown on LEO and non-LEO GaN P. Sandvik, D. Walker, P. Kung, K. Mi, F. Shahedipour, V. Kumar, X. Zhang, J. Diaz, C. Jelen, and M. Razeghi SPIE Conference, San Jose, CA, Vol. 3948, pp. 265 -- January 26, 2000 ...[Visit Journal] The III-Nitride material system is an excellent candidate for UV photodetector applications due to its wide, direct bandgaps and robust material nature. However, despite many inherent material advantages, the III-Nitride material system typically suffers from a large number of extended defects which degrade material quality and device performance. One technique aimed at reducing defect densities in these materials is lateral epitaxial overgrowth (LEO). In this work, we present a preliminary comparison between AlGaN UV, solar-blind p-i-n photodiodes fabricated form LEO GaN and non-LEO GaN. Improvements in both responsivity and rejection ratio are observed, however, further device improvements are necessary. For these, we focus on the optimization of the p- i-n structure and a reduction in contact resistivity to p- GaN and p-AlGaN layers. By improving the structure of the device, GaN p-i-n photodiodes were fabricated and demonstrate 86 percent internal quantum efficiency at 362 nm and a peak to visible rejection ratio of 105. Contact treatments have reduced the contact resistivity to p-GaN and p-AlGaN by over one order of magnitude form our previous results. [reprint (PDF)]

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