Transient photocurrent response of three-color detectors based on amorphous silicon

Color detectors based on multilayers of amorphous-silicon alloys facilitate the detection of the three fundamental components of visible light in one single pixel of a sensor array. In order to achieve sensitivity for the blu e, green, and red components of light, three different bias voltages are ap plied to the device. By switching them sequentially the detector is read ou t. n-i-p-i-i-n structures with a controlled band gap and mobility-lifetime product exhibit excellent stationary properties, namely: good color separat ion and have dynamic behaviors above 95 dB. Besides the stationary behavior the transient response of a color detector is a further optimization crite rion. The experimentally found transient photocurrent response after switch ing on monochromatic light at different applied bias voltages showed reason able delay times in the range of tens of milliseconds before reaching stead y state. Numerical simulations have been carried out which reproduce this c haracteristic behavior and facilitate a study of time dependent processes w ithin the device, such as charge transport and storage in localized states. The delay times can be explained by the recharging of electrical defect st ates in the amorphous material. Consequently, the electrical potential with in the device changes, which remarkably affects the carrier transport. Base d on these results optimization criteria for the transient behavior of the color detectors are discussed. (C) 1999 American Institute of Physics. [S00 21-8979(99)03507-0].