The detection of light at ultraviolet (UV) wavelengths is important for many military, medical and environmental applications. Applications such as biological agent detection and non-line-of-sight communications require the detection of scattered UV light. Currently, photomultiplier tubes operated as single photon counters are used to detect these low light levels, but they have many unfavorable characteristics for such applications. SiC based avalanche photodiodes (APDs) operated in Geiger mode could potentially meet the needs of these applications. Our first results, using SiC Geiger mode single photon counting avalanche photodiodes (SPADs), showed prohibitively high dark counts, due to a large tunneling current component in the multiplied dark current. Here we show the results of two p-i-n structures with 260μm and 480μm i-regions, which reduced the primary dark current by two orders of magnitude, operated under gated quenching conditions at 325nm. The lower dark current resulted in a dark count rate of 28kHz at 3.6% single photon detection efficiency (SPDE) in a 100μm diameter device. This is a three order reduction in the dark count rate over our previous results using a p-n junction SPAD.
This paper surveys recent work in several photodetector areas including high-speed, low-noise avalanche photodiodes, high-power photodiodes, solar-blind ultra-violet PIN photodiodes, and quantum dot infrared photodetectors (QDIPs).
This paper surveys recent work in several photodetector areas including high-speed, low-noise avalanche photodiodes, solar-blind ultra-violet PIN photodiodes, and quantum dot infrared photodetectors (QDIPs).
The detection of light in the ultraviolet (UV) portion of the electromagnetic spectrum is critical to a number of commercial and military applications. Until very recently, the primary means of light detection in the UV was with either silicon photodiodes or photomultiplier tubes, both of which have serious drawbacks. With the advent of optoelectronic devices fabricated in the ternary alloy of AlGaN, the possibility exists to produce high- performance solid-state photodetector arrays that are sensitive to the visible-blind and solar-blind regions of the spectrum. In this paper, we discuss recent advances in the area of ultraviolet photodetectors fabricated on GaN and AlGaN.
We report on the improved quantum efficiency of both GaN homojunction and AlxGa1-xN/GaN heterojunction photodiodes using a recessed window device structure. A very high quantum efficiency of 77 percent at 357 nm and also a much improved quantum efficiency at the solar blind wavelengths were achieved. A spatial non-uniformity problem on the large area devices was observed with 2D raster scan photocurrent measurements. The spatial non-uniformity is attributed to an electric field crowding effect that is primarily caused by the high resistivity of the p-GaN layer with the aid of Medici simulations.
The detection of light in the UV portion of the electromagnetic spectrum is critical to a number of applications. Until very recently, the primary means of light detection in the UV was with either silicon photodiodes or photomultiplier tubes, both of which have serious drawbacks. With the advent of optoelectronic devices fabricated in the ternary alloy of AlGaN, the possibility exists to produce high-performance solid-state photodetector arrays sensitive to the visible-blind and solar-blind regions of the spectrum. In this paper, we discuss recent advances in the area of UV photodetectors fabricated on GaN and AlGaN. Various device structures are presented, and their peculiar characteristics discussed in terms of responsivity, dark current, gain, temporal response, and frequency response. Models describing the current transport mechanisms and the quantum efficiencies of these photodiodes are discussed. Special emphasis is given to novel device structures that improve on the temporal, spectral, and electrical characteristics of AlGaN-based photodiodes. Specifically, results for a transparent recessed-window p-i- n device, and a semi-transparent electrode device structure are described. Finally, the results of a separate absorption, charge, and multiplication avalanche photodetector are presented. This device structure resulted in a stable gain of > 10 at a reverse bias of approximately 40 V.
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