Utilization of Photoconductive Gain in a-Si:H Devices for Radiation Detection

The photoconductive gain mechanism in a-Si:H was investigated in connection with applications to radiation detection. Various device types such as p-i-n, n-i-n and n-i-p-i-n structures were fabricated and tested. Photoconductive gain was measured in two time scales: one for short pulses of visible light (< 1 μsec) which simulates the transit of an energetic charged particle, and the other for rather long pulses of light (1 msec) which simulates x-ray exposure in medical imaging. We used two definitions of photoconductive gain: current gain and charge gain which is an integration of the current gain. We found typical charge gains of 3 ∼ 9 for short pulses and a few hundred for long pulses at a dark current level of 10 mA/cm2. Various gain results are discussed in terms of the device structure, applied bias and dark current.