Charge collection in a-Si:H/a-Si(sub 1-x)C(sub x) multilayers photodetectors

摘要

Amorphous semiconductors have been used as thin film transistor(TFT), solar cell, phototransistors. In this paper we study the charge collected properties of a-Si:H/a-Si(sub 1-x)C:H(sub x) multilayer PIN photodiode. In a-Si:H PIN photodiode, the photogenerated carriers can be totally collected under strong electric field under reverse bias. However, our measurements show that in the a-Si:H/a-Si(sub l-x)C:H(sub x) multilayer pin photodiode photogenerated electrons and holes drift toward the electrodes under a certain bias, the total collected charge shows no saturation with bias and exhibits a continuous increase with reverse bias. We classify that the device works at two regions. In Region 1, the device behaves like a photodiode. This charge collection efficiency drop from theoretical value may indicate charge capture or confinement at the interfaces and trapping at the a-Si:H potential wells. These charges trapped or confined can be released at the interface and quantum well at higher electric field. In Region 2, above a critical bias voltage, the device works as a breakdown diode with a series photosensitive resistor which contributes higher collection efficiency, namely optical gain greater than unity.