High-gain p-i-n infrared photosensors with Bragg reflectors on amorphous silicon–germanium alloy

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Abstract
An amorphous silicon–germanium alloy (α-SiGe:H) infrared photosensor with a Bragg reflector to obtain high optical gain and responsivity is demonstrated. The Bragg reflector containing α-Si:H and α-SiGe:H layers was grown on the top of p-i-n structure with an amorphous silicon/germanium alloy. All of the amorphous silicon and amorphous silicon–germanium layers were deposited by a low-temperature plasma enhanced chemical vapor phase deposition system. The experimental results of the new structures exhibit a much superior performance to that of conventional p-i-n avalanchephotosensor structures. That is, the structure with a Bragg reflector shows a significant improvement in optical gain from 80 to 328 under the incident optical power of 1 μW, and the full width at half maximum can be reduced from 250 to 150 nm.