A Comparison of Lattice-Matched GaInNAs and Metamorphic InGaAs Photodetector Devices
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A Comparison of Lattice-Matched GaInNAs and Metamorphic InGaAs Photodetector Devices David B. Jackrel, Homan B. Yuen, Seth R. Bank, Mark A. Wistey, Xiaojun Yu, Junxian Fu, Zhilong Rao, and James S. Harris, Jr. Stanford University, Solid State Research Lab, 420 Via Palou, Stanford, CA 94305-4070, U.S.A. ABSTRACT The dilute-nitride GaInNAs shows great promise in becoming the next choice for 1 eV photodetector and multi-junction photovoltaic applications due to the ability for it to be grown lattice-matched on GaAs substrates. This paper will present results from high-power photodetector devices fabricated from high-quality thick GaInNAs and metamorphic InGaAs materials grown by MBE. The internal quantum efficiency of rear-illuminated PIN photodiodes with thick GaInNAs films as the intrinsic region (roughly 62% at 1064 nm) is somewhat lower than comparable metamorphic InGaAs devices (roughly 75% at 1064 nm). However, the dark current density of the GaInNAs devices is also somewhat lower (roughly 3 µA/cm2 at 2x104 V/cm bias) than the InGaAs devices (roughly 20 µA/cm2 at 2x104 V/cm bias), while the breakdown voltages (beyond -20 V) are comparable. Materials characterization of each structure, including x-ray diffraction and room-temperature as well as temperature-dependent photoluminescence studies will be presented in order to explain the characteristics observed in the devices composed of the two different material systems. INTRODUCTION The dilute-nitride GaInNAs shows great promise in becoming the next choice for 1 eV photodetector and multi-junction photovoltaic applications due to the ability for it to be grown lattice-matched on GaAs substrates. GaAs-based photodetector devices have several advantages over InP-based devices, such as substrate cost, convenience of processing, and heterojunction energy band engineering parameters. The current world record photovoltaic cell, produced by Spectrolab, is a triple junction structure composed of GaInP/GaAs/Ge with a power conversion efficiency of over 37% [1]. In order to further maximize the power conversion of the solar spectrum 4- and 5-junction cells with a 1.0 eV sub-cell lattice-matched to GaAs and Ge , such as a sub-cell composed of GaInNAs, must be developed [2]. Metamorphic InGaAs is the current choice for 1 eV materials grown on GaAs substrates. Historically, however, higher threading dislocation densities and rough interfaces plague these devices due to the large concentration of misfit dislocations inherent to metamorphic structures [3]. In order to create photodetectors capable of absorbing large amounts of laser power, and photovoltaic devices capable of withstanding high solar concentration ratios, rear-illuminated device architectures were developed. The absorbing layers of the rear-illuminated devices are directly adjacent to the heat sink thereby enhancing the thermal conductivity by orders of magnitude over conventional front-illuminated detectors. This results in devices with excellent linearity and very high damage thresholds. The most detrimen
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