Charge transfer and electronic screening at the As/Si(100)-(2×1) and As/Si(111)-(1×1) surfaces

As and Si Auger parameters for As terminated Si(100) and Si(111) surfaces have been measured and analyzed in terms of ground state charge transfer across the interfaces and core hole screening efficiency. Our results indicate a small electron transfer ({~}0.05 electrons per atom) from Si to As at these interfaces. We find that for the As/Si(100) system core holes in atoms in the interface layers are much better screened than in bulk Si, due to high polarizability in the As-As bond. The screening is more bulklike at the As terminated Si(111) surface, consistent with the unreconstructed ``bulk-terminated'' surface structure of this system.