Abstract
The a-Si:H photodiode film is suitable for photoconversion in stacked-type image sensors. If a photocurrent in an a-Si:H p-i-n photodiode film is multiplied by the avalanche phenomenon, a highly sensitive image sensor can be realized. A photocurrent multiplication phenomenon was observed in a p-type hydrogenated amorphous silicon carbide (a-SiC:H)/i-type hydrogenated amorphous silicon (a-Si:H)/n-type crystalline silicon (c-Si) heterojunction p-i-n photodiode film. In this photodiode film, a maximum multiplication gain of photocurrent of 40 times was confirmed. To clarify the multiplication mechanism, the shot noise of the photocurrent in the a-Si:H p-i-n photodiode film was investigated. The measured shot noise in the multiplication region was larger than an ideal shot noise which was assumed to be free of excess noise. This indicates that the photocurrent was multiplied by avalanche process. The excess noise factor of our p-i-n photodiode film was also estimated.