Interface states at ZnSe/Ge heterojunctions: the role of atomic interdiffusion and disorder

The origin of electronic states localized at ZnSe/Ge 110 interface is investigated by means of ab initio pseudopotential calculations. Some selected interface configurations are considered, one corresponding to the abrupt interface and others corresponding to partially disordered interfaces, with Zn-Ge or Se-Ge swaps. Remarkably, the existence of interface electronic states within the heterojunction band gap critically depends on the atomic-scale morphology of the interface: unlike the abrupt case, disordered interfaces exhibit localized states extending over the whole interface Brillouin zone. The presence of interfacial density of states, experimentally detectable, is therefore an indication of disorder and atomic interdiffusion.