Scanning tunneling spectroscopy and first-principles investigation on GaAs(0 0 1)(2 × 6)-S surface formed by molecular beam epitaxy

Abstract

The surface reconstruction of, in situ prepared, S-terminated GaAs (0 0 1) is studied by scanning tunneling microscopy and a first-principles pseudopotential method. According to an electron counting model, in order to form this (2 × 6)-S on GaAs (0 0 1) surface, one electron needs to be transferred from each S dimer to the Ga dangling bonds on the missing dimer region. As a result of the first-principles investigation on the SS bond length of one S dimer, the separations are calculated as 0.2370 nm and 0.3897 nm, with and without one electron transfer, respectively. Experimental result agreed well with the former condition. This indicates that there may be a long-range electron transfer on this (2 × 6) structure. Moreover, the calculated electronic structure of this S dimer with one electron transfer shows a flat unoccupied band which is mainly caused by the antibonding band of the SS bond. This result also agreed well with conductivity spectrum of this (2 × 6) surface by scanning tunneling spectroscopy, which shows a peak on the conduction band side.