Dissociation of As4 molecules during molecular beam epitaxy of GaAsP on (n11)A and (n11)B GaAs substrates

We investigated substrate orientation and As species dependence of GaAsxP1−x layers grown on (100), (n11)A, and (n11)B GaAs substrates (n=3, 4, and 5) by molecular beam epitaxy at a substrate temperature of 535 °C. When GaAsP layers were grown using As2 and P2 molecular beams, the As content of the layers were almost independent of the substrate orientation and were 0.92–0.94. When As4 and P2 molecular beams were supplied, the As contents of (100) and (n11)B GaAsP layers were almost constant (x∼0.88), while (n11)A GaAsP layers had smaller As contents. The (411)A GaAsP layer had the smallest As content of 0.75. Based on the process in which As4 molecules dissociate into 2As2 or vaporize on the surface, the results indicate that dissociation and vaporization of As4 is strongly dependent on the substrate orientation, while the incorporation process of As2 is almost independent of the substrate orientation. The results also strongly suggest that the B-step edges provide the effective sites for the dissociatio...