Ab initio simulation of Si-doped GaAs(110) cross-sectional surfaces

We study different configurations of the (110) cross-sectional surface of Si-doped GaAs, from the isolated Si donor up to an entire donor-acceptor Si bilayer embedded along the (001) growth direction. Electronic potentials, density of electronic states, cross-sectional scanning tunneling microscopy (XSTM) images are calculated using first-principles numerical simulations. Doping configurations with compensating Si impurities in cationic and anionic sites, such as the donor-acceptor bilayer, are characterized by XSTM images with bright signal at negative bias, strongly attenuated when the bias is reversed. These features are characteristic of real samples above the onset of self-compensation. The comparison of the experimental images with the numerical simulations allows to shed light on the microscopic picture of self compensation hitherto associated to a variety of mechanisms - including the formation of complexes of Si with native defects - and to uniquely attribute the observed experimental features to Si donor-acceptor configurations. (c) 2005 Elsevier B.V All rights reserved.