Electrical conduction by interface states in semiconductor heterojunctions

Electrical conduction in semiconductor heterojunctions containing defect st ates in the interface region is studied. As the classical drift-diffusion m echanism cannot in any case explain electrical conduction in semiconductor heterojunctions, tunnelling involving interface states is often considered as a possible conduction path. A theoretical treatment is made where defect states in the interface region with a continuous energy distribution are i ncluded. Electrical conduction through this defect band then allows the tra nsit of electrons from the conduction band of one semiconductor to the vale nce band of the second component. The analysis is initiated by electrical m easurements on n-CdS/p-CdTe heterojunctions obtained by chemical vapour dep osition of CdS on (111) oriented CdTe single crystals, for which current-vo ltage and capacitance-frequency results are shown. The theoretical analysis is based on the numerical resolution of Poisson's equation and the continu ity equations of electrons, holes and defect states, where a current compon ent corresponding to the defect band conduction is explicitly included. Com parison with the experimental curves shows that this formalism yields an ef ficient tool to model the conduction process through the interface region. It also allows us to determine critical values of the physical parameters w hen a particular step in the conduction mechanism becomes dominant.