Thermodynamic Stability of (AlAs)n(GaAs)n Superlattices and the Random Al0.5Ga0.5As Alloy

Abstract

We calculate the total energy of random ${\mathrm{Al}}_{0.5}{\mathrm{Ga}}_{0.5}\mathrm{As}$ alloys and ordered ${\left(\mathrm{AlAs}\right)}_n{\left(\mathrm{GaAs}\right)}_n$ superlattices through a series expansion in multi-atom interaction energies obtained from the local-density formalism. We find that the alloy is more stable than the monolayer ($n=1\mathrm{}$) superlattice at all temperatures, but it could order into longer-period ($n\ge 2$) superlattices below a critical temperature $T(n,\mathbf{G})$ calculated for various growth orientations $\mathbf{G}$.