We investigate the electronic properties of the (110) cross-sectional surface of Si-doped GaAs using first-principles techniques. We focus on doping configurations with an equal concentration of Si impurities in cationic and anionic sites, such as occurring in a self-compensating doping regime. In particular we study a bilayer of Si atoms uniformly distributed over two consecutive (001) atomic layers. The simulated cross-sectional scanning tunneling microscopy images show a bright signal at negative bias, which is strongly attenuated when the bias is reversed. This scenario is consistent with experimental results which had been attributed to hitherto unidentified Si complexes.
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The (110) slab geometry is obtained by applying periodic boundary conditions in the , (110) and (001) directions. The former is used to describe repeated parallel slabs (containing nine atomic planes perpendicular to the direction in our case), separated by a vacuum region (of about in our case) large enough to guarantee a sufficient separation of two adjacent surfaces. The last two periodic boundary conditions are used to describe the infinite surface; the surface unit cell for the doped configurations has to be large enough (up to 20 atoms in the present cases) in order to guarantee a sufficient separation between periodic images of the impurities.
