Photocapacitance of GaAs thin-film structures fabricated on a semi-insulating compensated substrate

The results of analytical and numerical calculations of the low-frequency and the high-frequency barrier capacitance of GaAs epitaxial and ion-implanted structures fabricated on a semi-insulating compensated substrate are presented. The calculations are done for the samples in the dark and under extrinsic illumination. It is shown that the high-frequency photocapacitance of these structures exhibits a narrow peak, and the low-frequency photocapacitance has a positive peak followed by a negative valley. The underlying physical mechanisms are discussed. Methods for predicting the MESFET threshold voltage and extracting the concentration of vacant deep traps in the vicinity of the film-substrate interface and the epitaxial film thickness using capacitance-voltage measurements under extrinsic illumination are proposed.