First, a p/i/n thin-film photodiode (TFPD) is evaluated, and it is found that the photoinduced current (I photo ) is relatively large. Next, a p/n TFPD is evaluated, and it is found that the I photo is independent of the applied voltage (V apply ). However, it is difficult to simultaneously achieve a large and independent I photo . Therefore, a p/i/n thin-film phototransistor (TFPT) is developed, and it is found that the I photo can be both relatively large and independent of the V apply by optimizing the gate voltage. These characteristics are obtained because the depletion layer is formed in the entire intrinsic region and the electric field is always high. It is expected that these characteristics are preferable for some types of photosensor application such as artificial retina.
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.
The color sensitivity of a thin-film phototransistor using a polycrystalline-silicon film with a p/i/n structure has been evaluated. First, the illuminance and voltage dependences of the detected current for white, red, green, and blue light are measured. It is found that the photoinduced current is proportional to the illuminance and that the detected current is slightly dependent on the applied voltage. Next, the conversion efficiencies from the colored light to the photoinduced current are calculated. It is found that the illuminance efficiency is considerably different for the different colors, whereas the quantum efficiency is similar for the different colors. The quantum efficiency is on the order of 0.1 but lower for the red light and higher for the blue light. This suggests that the electron–hole pairs generated by the red light have lower energy and tend to be recombined and disappear, whereas those generated by the blue light have higher energy and tend to be separated and contribute to the photoinduced current. The color sensitivity must be considered when the thin-film phototransistor is used in actual photosensor applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.