Interface defects and their effect on the electrical properties of ZnSe/GaAs heterojunctions grown by MBE

We studied electrical properties of MBE-grown ZnSe/GaAs heterojunctions due to the interface states, by admittance spectroscopy. The capacitance-voltage characteristics show a hysteresis which can be related to an unusually slow capacitance transient. A large frequency dispersion of the capacitance and a broad peak in the conductance spectra are observed at high temperatures. These observations strongly suggest the presence of a continuum of defects in the interface between ZnSe and GaAs. The capacitance versus frequency data was analyzed in terms of Lehovec's model of an interface state continuum with a single time constant giving a density of interface states about 4X10(12) cm(-2) eV(-1) for typical both n- and p-type samples. We attribute the long time constant observed in the capacitance transients to slow changes in the electrical charge on the interface states. The presence of interface states may seriously affect the performance of ZnSe/GaAs based devices. The correlation between their behavior and the growth conditions is of prime importance and is presently under study.