SCANNING-TUNNELING-MICROSCOPY SIGNATURES AND CHEMICAL IDENTIFICATIONSOF THE (110) SURFACE OF SI-DOPED GAAS

The electronic properties of the (1 10) surface of both pure and Si-do ped bulk GaAs are studied using first-principles total-energy calculat ions within the local-density functional and pseudopotential approxima tions. The wave functions of the relaxed configurations are used to ge nerate theoretical scanning-tunneling-microscopy (STM) images. For the clean surface, the buckling angle of the surface Ga-As bond is found to be 26-degrees and the theoretically generated STM images are in goo d agreement with those obtained from experiment. For the Si-doped GaAs (l 10) surface, the extra electron of the Si substitutional at a Ga si te on the surface is found to be well-localized around the Si atom. In addition, dangling-bond states of surface As atoms bordering the Si s ubstitutional are found to be altered due to the distinctively differe nt chemical property of the Si substitutionals. These features should act as a signature for the location of the substitutional surface Si a toms via either voltage-dependent STM imaging or current-voltage (I-V) measurements of various positions on the surface.