Evaluation of Gap States in Hydrogen-Terminated Silicon Surfaces and Ultrathin SiO2/Si Interfaces by using Photoelectron Yield Spectroscopy

Abstract

ABSTRACTThe energy distributions of gap state densities for H-terminated Si surfaces and thermally-grown SiO2/c-Si interfaces have been evaluated by total photoelectron yield spectroscopy (PYS) with a dynamic range of eight orders of magnitude which is sufficient to detect the density of states as low as 1010cm−2eV−1. It is confirmed from the threshold energies for direct and indirect photo-excitations that, for monohydride-terminated Si(111) surfaces prepared by an NH4F treatment, no significant band-bending is observable. For H-terminated n-type sample, the gap state densities of the order of 1011cm−2eV−1 were estimated in the region within 0.4 eV from the valence band edge, which may be attributable to a very little oxidation in the sample preparation. It is also found that, for as-grown 2.5nm-thick SiO2/n+ Si, there exist interface states around midgap with densities as high as ∼1012cm−2eV−1.