Identification of P dopants at nonequivalent lattice sites of theSi(111)−(2×1)surface

Abstract

Substitutional phosphorus atoms at the $\mathrm{Si}(111)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface have been studied with scanning tunneling microscopy at $8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Four different types of the P-induced contrast pattern are distinguished due to their voltage-dependent contrast. Three of them are identified as substitutional P atoms on distinct lattice sites by their spatial symmetry and by comparison with ab initio calculations of the local density of electronic states of substitutional P atoms. The fourth pattern of a P-induced contrast cannot be attributed to the remaining fourth site of the $\ensuremath{\pi}$-bonded chain. This raises questions not only on the origin of this pattern but also on the absence of substitutional P atoms on one lattice position in this surface.