Development of the Na/GaAs(111)A-(2 x 2) interface at room and low temperature

The alkali-metal/III-V semiconductor interface is a model system with which to study overlayer metallization and Schottky barrier development. Until now, typically the cleaved (110) surfaces of the semiconductor have been utilized in this respect, though in this work we have used the Ga-vacancy (2 X 2) reconstructed surface of GaAs(111)A as the starting surface. This surface is known to exhibit many similarities with the cleaved (110) surface, due to the separation of empty and filled dangling bonds onto the Ga and As surface atoms respectively. We have found through using soft X-ray photoemission from both core-level and valence-band features that the interface is remarkably unreactive, with almost no change in the Ga 3d lineshape with Na deposition at low temperatures. With regard to the growth-mode, work-function variation and band-bending however, the behaviour is close to that found for the cleaved surface. The onset of the Na LVV Auger transition only occurs after metallization begins and is consistent with ionic bonding to the substrate, though the substrate core-level development points to a reduced charge transfer with respect to the (110) surface.