Contactless capacitance–voltage and photoluminescence characterization of ultrathin oxide–silicon interfaces formed on hydrogen terminated (111) surfaces

Abstract

Electronic properties of the interfaces between Si and ultrathin (≲10 Å) oxides formed by various low-temperature processes were characterized in contactless fashion, using contactless capacitance–voltage and photoluminescence surface state spectroscopy techniques together with x-ray photoelectron spectroscopy measurement. Hydrogen (H) terminated Si(111) surfaces were used as the initial surface. Ultrathin oxides were formed at low temperatures by chemical oxidation processes (hot HNO3, H2SO4+H2O2), long-time air exposure, and low-temperature oxidation processes below 350 °C. The initial H-terminated surfaces showed presence of Fermi-level pinning at E0=EV+0.65 eV due to high density of amphoteric discrete state probably originating from Si dangling bonds. On the other hand, all the ultrathin oxide–Si interfaces exhibited very limited capacitance variations with voltage at low capacitance levels similar to GaAs metal–insulator–semiconductor systems, and indicated that the Fermi level is pinned near the hybrid orbital charge neutrality level EHO due to presence of interface states with narrow U-shaped continuous distributions. Low-temperature oxidation at 350 °C slightly weakens such pinning. The present work indicates difficulty of realizing unpinned ultrathin oxide–silicon interface by low-temperature processes.