Surface segregation and ordering in III-V semiconductor alloys

Using the first-principles total-energy pseudopotential method, we have studied the formation energy of the (001) Ga1-xInxP alloy surface as a function of composition and reconstruction. The results are presented as T=0 surface stability diagrams that show the lowest energy reconstruction and cation occupation pattern as functions of the chemical potentials. Slightly different stability diagrams emanate depending on whether or not there is equilibrium between the surface and the bulk. The stability diagrams show a pronounced asymmetry between the Ga- and In-rich regions. The asymmetry is interpreted in terms of the size difference between In and Ga and the effect of this size difference on the bonding geometry. For surfaces in equilibrium with the bulk, we find a strong dependence of surface segregation on the surface reconstruction, and we predict a Ga enrichment of the surface in the moderate cation-rich limit and In enrichment in the anion-rich region. This result suggests a way to achieve abrupt interfaces in semiconductor heterostructures. For surfaces not in equilibrium with the bulk, we identify regions in the stability diagram where surface-induced CuPt ordering (both type A and type B) occurs. copyright 1996 The American Physical Society