Photocapacitance of GaAs thin-film epitaxial structures

A simple analytical model for calculating the high-frequency barrier capacitance of GaAs thin-film epitaxial structures both in the dark and under extrinsic illumination is presented. The model accounts for the space charge region at the film–substrate interface. The model shows that the photocapacitance of these structures has the form of a narrow peak located at the bias voltage, at which the barrier capacitance drops abruptly with reverse bias. The underlying physical mechanism is discussed. A method for predicting the MESFET threshold voltage based on the measured photocapacitance is proposed and tested.