Theory of Sb-induced triple-period ordering in GaInP

During organo-metallic vapor phase epitaxy (OMVPE) of GaInP (001) layers, the structure of the growth surface has a profound influence on the microstructure, and the optical and electrical properties of the resulting bulk material. The β2(2×4) surface, terminated with P dimers, provides a thermodynamic driving force for CuPtB ordering. Recently, surfactants such as Sb have been used to reduce this driving force. The use of surfactants to control the surface structure during growth has allowed for band-gap tailoring and the fabrication of heterostructures with no change in solid composition across the interface. Another exciting discovery was that high coverages of Sb induced a bulk triple period ordering. To further our understanding of these phenomena, the P terminated GAP(001) surface was studied via first principles calculations based on the Kohn-Sham density functional theory within the local density approximation (LDA). It was determined that under increasingly P-rich conditions, the β2(2×4) and then the c(4×4) reconstructions are stable. When the surface is covered with Sb, several different reconstructions are found to be stable in the allowable range of chemical potentials. Under lower group-V coverages the β2(2×4) is stable, while at high Sb coverage, (4×3) and (2×3) reconstructions are stable. We propose that these (×3) reconstructions explain the triple period ordering seen in GaInP grown with Sb as a surfactant. Total-energy calculations confirm that (×3) reconstructions provide a thermodynamic driving force for A-variant triple period ordering.