Color sensitivity of thin-film phototransistor using polycrystalline- silicon film with p/i/n structure

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. Copyright © 2010 The Japan Society of Applied Physics.