The capacitance of p-n heterojunctions including the effects of interface states

The theoretical capacitance of abrupt p-n heterojunctions including the effects of interface states is examined. The interface effects depend on the bulk impurity concentrations and their ratio, as well as the density and distribution of interface states. In the Ge-GaAs junctions studied, the impurity concentrations and density of interface states are such that interface effects have only a negligible influence on the capacitance of these devices. Interface states have a considerable effect on the capacitance of the Ge-Si junctions studied, however. They affect the apparent diffusion voltages obtained by extrapolating 1/C²to zero and add a significant frequency-dependent term on many diodes. The frequency-dependent term is due to the rate limited charging and discharging of interface states.