Sulfur passivated InP(100): surface gaps and electron counting

The atomic and electronic structures of the sulfur passivated InP(100) surface have been studied with electron diffraction, photoemission and inverse photoemission spectroscopies. The InP(100) surfaces were passivated using a wet chemical treatment. In agreement with previous studies, we find that the unannealed surface has the 1 × 1 symmetry of the bulk lattice, which transforms to a 2 × 1 pattern upon annealing to temperatures in the range 350–500°C. Photoemission and inverse photoemission studies of the electronic states in the vicinity of the valence band maximum and conduction band minimum demonstrate that the passivation process removes states from the region of the fundamental gap of InP. No bands cross the Fermi level. The dispersion of several two-dimensional states has been measured. These states show a strong similarity to surface states of the Ge(100)-S(1 ML)(1 × 1) system. By applying electron counting rules, we demonstrate that several of the surface structural models that have been proposed to date are inconsistent with our experimental results, since they should result in partially filled surface bands crossing the Fermi level.