Epitaxial Growth for Solar-Blind AlGaN Photodetector Imaging Arrays by Metalorganic Chemical Vapor Deposition
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Epitaxial Growth for Solar-Blind AlGaN Photodetector Imaging Arrays by Metalorganic Chemical Vapor Deposition Uttiya Chowdhury; Charles J. Collins; Michael M. Wong; Ting Gang Zhu; Jonathan C. Denyszyn; Jin Ho Choi; Bo Yang; Joe C. Campbell; and Russell D. Dupuis 10100 Burnet Road, Building 160, Austin, TX 78758 USA Phone: +1-512-471-0537, Fax: +1-512-471-0957, e-mail: [email protected] ABSTRACT Solar-blind imaging arrays based on AlGaN p-i-n structures are of high interest for defense applications. We have studied the material issues involved in development of such imaging arrays and have developed discrete photodetector devices with a high external quantum efficiency (EQE) and imaging arrays of high operability. For the discrete devices, a record EQE of 58.1% peaking at 274 nm under zero volt bias was obtained without using an anti-reflecting (AR) coating. The EQE was seen to have a slight voltage dependence: going up to 64.5% at –5V reverse bias. The responsivity had a drop-off by one order of magnitude for a wavelength change of 4 nm on both the shorter and longer wavelength side. The material quality and uniformity was found to be very good leading to the development of 256 × 256 arrays. A high yield along with uniform, high EQE was obtained for the detector devices in the array leading to a high operability of 99.8%. INTRODUCTION The solar-blind spectrum ranging from ~290 nm to shorter wavelength is of interest from a variety of applications. This spectral region is called solar-blind because due to absorption in the terrestrial ozone layer, solar radiation obtained near Earth’s surface contains very little radiation of this wavelength range. As a result, a solar-blind photodetector (SBD), sensitive to light of wavelength shorter than ~290 nm, but insensitive to longer-wavelength radiation will be able to operate near the Earth’s surface without a large background signal from the solar radiation. As a result, if it is intended to image some object emitting light of wavelength shorter than ~290 nm, a solar-blind photodetector can provide a much higher signal-to-noise ratio compared to photodetectors operating at other spectral ranges. This is very useful for a number of defense applications including missile detection from the radiation of the exhaust plume. Accordingly, there has been a high interest in the defense industry in fabrication of solar-blind imaging arrays. Semiconductor-based SBDs are of particular interest due to the ease of fabrication into imaging arrays, their compact size, and low voltage operation. Particularly, for convenience of integration, it is desired to flip-chip mount the imaging array on Si based read-out integrated circuit (ROIC). As a result, it is desired to have back-illuminated SBDs capable of operating at low bias voltages. Operability at low bias voltages allows driving of the photodetectors using the same power supply as the one used for the ROIC, obviating the need of additional bulky power supplies. In the present work, we report on development of high external
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