Evaluation of thin‐film photodevices and application to an artificial retina

Abstract

Abstract— First, conventional poly‐Si thin‐film photodevices, p‐i‐n thin‐film photodiodes (TFPDs) and p‐n TFPDs, were evaluated. It was found that the photo‐induced current ( Iphoto ) is not simultaneously relatively high and independent of the applied voltage ( Vapply ). Next, a novel poly‐Si thin‐film photodevice, p‐i‐n thin‐film phototransistor (TFPT), is proposed. It is found that the Iphoto is simultaneously relatively high and independent of the Vapply because the depletion layer is formed in the entire intrinsic region and the electric field is always high. These characteristics are preferable for photosensor applications. Finally, the p‐i‐n TFPT was applied to an artificial retina. The photo‐illuminance profile is correctly detected and the output voltage profile is correspondingly outputted. This artificial retina is expected to be suitable for human beings because it can potentially be fabricated on a flexible, harmless, plastic, and organic substrate.