SCANNING TUNNELING SPECTROSCOPY AND FIRST-PRINCIPLES INVESTIGATION ONGAAS(001)(2X6)-S SURFACE FORMED BY MOLECULAR-BEAM EPITAXY

The surface reconstruction of, in situ prepared, S-terminated GaAs (00 1) is studied by scanning tunneling microscopy and a first-principles pseudopotential method. According to an electron counting model, in or der to form this (2 x 6)-S on GaAs (001) surface, one electron needs t o be transferred from each S dimer to the Ga dangling bonds on the mis sing dimer region. As a result of the first-principles investigation o n the S-S bond length of one S dimer, the separations are calculated a s 0.2370 nm and 0.3897 nm, with and without one electron transfer, res pectively. Experimental result agreed well with the former condition. This indicates that there may be a long-range electron transfer on thi s (2 x 6) structure. Moreover, the calculated electronic structure of this S dimer with one electron transfer shows a flat unoccupied band w hich is mainly caused by the antibonding band of the S-S bond. This re sult also agreed well with conductivity spectrum of this (2 x 6) surfa ce by scanning tunneling spectroscopy, which shows a peak on the condu ction band side.