FET photodetectors: A combined study using optical and electron-beam stimulation

The photosensitivity of GaAs FET\´s has been studied using both optical and electron-beam (e-beam) stimulation at various signal frequencies up to 1.3 GHz. The results indicate that, at high frequencies, the photoconductive mechanism which usually gives a small current gain is the dominant process, whereas at low frequencies photovoltaic mechanisms, which lead to "phototransistor" action are responsible for the observed high photosensitivity and current gain in the device.