Structural stability of lattice-matched heterovalent semiconductor superlattices

Lattice-matched heterovalent alloys and superlattices have some unique physical properties. For example, their band gap can change by a large amount without significant change in their lattice constants, thus they have great potential for optelectronic applications. Using first-principles total energy calculation and Monte Carlo simulation as well as lattice harmonic expansion, we systematically study the stability of the heterovalent superlattices. We show that the chemical trend of stability of lattice-matched heterovalent superlattices is significantly different from lattice-mismatched isovalent superlattices, because for lattice-mismatched isovalent superlattices the stability is mostly determined by strain, whereas for lattice-matched nonisovalent superlattices the interfacial energy depend not only on the bond energy but also on the Coulomb energy derived from donor- and acceptor-like wrong bonds. In the short-period heterovalent superlattices, the abrupt [111] interface has the lowest energy even though it is polar, whereas for the long-period heterovalent superlattices, the [110] interface has the lowest energy. On the contrary, [201] superlattices are usually the most stable for lattice-mismatched isovalent superlattices.