Structures and electronic states of InAs (0 0 1) and (1 1 1)B surfaces passivated with sulfur studied by AES, LEED, UPS, XPS, and IPES

Abstract

Surface structures and electronic states of InAs(0 0 1) and (1 1 1)B passivated with sulfur have been studied by Auger electron spectroscopy, low-energy electron diffraction, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and inverse photoemission spectroscopy (IPES). The sulfur-adsorbed (0 0 1) surface is reconstructed into the (1×1) and (2×1) structures at about 230°C and 380°C, respectively. IPES spectra show that density of empty states at about 1.5 eV above the Fermi level ( E F) is decreased upon passivation. The binding energy of the In 4d 5/2 core-level for the (2×1) surface is shifted by +0.10 eV to a higher binding energy side. This indicates that E F of the (2×1) sample is located at 0.44 eV above the valence band maximum (VBM) and at 0.08 eV above the conduction band minimum (CBM), implying formation of an accumulation layer. For the clean (1 1 1)B-(1×1) surface, density of states at E F is not observed in a valence band spectrum. However, it is found for the sulfur-adsorbed (1 1 1)B-(1×1) surface. The binding energy of the In 4d 5/2 core-level for the surface is shifted by +0.26 eV. This indicates that E F of the sample is located at 0.60 eV above the VBM and at 0.24 eV above the CBM, also implying formation of the accumulation layer. The changes in electronic states by passivation and pinning of E F are discussed.