Atomic and electronic structure of the GaAs/ZnSe(001) interface

We studied the atomic and electronic properties of the polar GaAs/ZnSe(001) interface using first-principles total-energy calculations. Binding energy, atomic relaxations, local electric fields, and valence-band offsets are calculated for a variety of different interface structures. The abrupt interface is found to be energetically unstable for large supercells, whereas structures with an interface consisting of one or two mixed layers are energetically more stable. Among these structures an interface consisting of one mixed layer and a c(2×2) structure is found to be the most stable. The valence-band offset is not explained by a single structure but in terms of a degeneracy in the interface energy with respect to polarity which results in a vanishing interface dipole moment even for polar interfaces. Based on the first-principle results we derive a simple model that explains the arrangement of atoms within the mixed layer and gives insight into the mechanisms stabilizing certain interface structures.