ENERGY-DISTRIBUTION OF INTERFACE STATES IN THE BAND-GAP OF GAAS DETERMINED FROM X-RAY PHOTOELECTRON-SPECTRA UNDER BIASES

The energy distribution of interface states in the GaAs band gap is determined for metal-oxide-semiconductor devices with an ultrathin thermal oxide layer of similar to 3.8 nm, from measurements of x-ray photoelectron spectra under biases. The energy distribution has a peaked structure with four peaks at similar to 0. 15, similar to 0.5, similar to 0.75, and similar to 1.1 eV above the valence-band maximum (VBM). The 0.75-eV peak has the highest density of similar to 1.9 x 10(12) cm(-2) and is attributed to a (+/0) transition of As-Ga antisite defects. The weak 0.5-eV peak is tentatively attributed to a (++/+) transition of the As-Ga antisite defects. The 0.15- and 1.1-eV peaks that have densities of 1.3 x 10(12) and 0.8 x 10(12) cm(-2), respectively, are attributed to Ga-As, antisite defects and Ga vacancy defects, respectively. The interface Fermi level of GaAs is located at 0.85 eV above the VBM, indicating that it is strongly affected by the As-Ga antisite defects. From the density of the interface states near the Fermi level, i.e., similar to 1 x 10(13) cm(-2) eV(-1), it is shown that d phi/d chi(M) (phi: barrier height in GaAs, chi(M): metal electronegativity) is 0.24, indicating that the Fermi level is pinned partly by the As-Ga antisite defects and that fixed oxide positive charges with a density of (2-3) x 10(12) cm(-2) are present at the GaAs/oxide interface.