Theoretical investigation of inter-surface diffusion on non-planar GaAs surfaces

Abstract

We investigate the Ga adatom inter-surface diffusion between GaAs(001)-(2×4) top and GaAs(111)B-(2×2) side surfaces theoretically, based on microscopic calculations and a statistical mechanical discussion. The calculated migration potential based on the microscopic calculations imply that Ga adatoms are predominantly adsorbed on (001) surfaces. The results indicate that Ga adatoms basically diffuse from the (111)B side surface to the (001) top surface, so long as both top and side surfaces are single-domain structures. However, around the critical As pressure of surface transition, where (2×2) and ( 19 × 19 ) structures coexist on the (111)B side surface, boundaries exist that are covered with neither (2×2) nor ( 19 × 19 ) units. Since these non-covered boundaries can contain very reactive Ga adsorption sites, Ga adatoms tend to diffuse from the (001) top to the (111)B side surface, so long as non-covered boundaries appear on the (111)B side surfaces. Our theoretical investigation implies that the direction of the inter-surface diffusion between the GaAs(001) top and the (111)B side surfaces is reversed twice with increasing As pressure, which is in good agreement with the recent experimental reports.