Study of the transient response of microcompensated amorphous silicon detector in the near infrared range

A detailed investigation of the near infrared detection process of an hydrogenated amorphous silicon sensor is presented. Single junction devices with micro-compensated absorber layer show photocurrent response to radiation up to 2 μm at room temperature. This sensitivity is ascribed to both the high number of trap states existing in the absorber material and to the electric field distribution in the device. Results of transient and frequency responses under different bias voltage and illumination conditions confirm the existence of a conduction mechanism controlled by traps. In particular, the exponential increase of the signal current with forward applied voltage suggests the re-excitation of the injected carriers from shallow localized states into extended states. Finally, a preliminary optimization of the response of the device achieved by including it in a front-end circuit allows detection of modulated radiation up to 100 kHz