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 ∼3.8 nm, from measurements of x-ray photoelectron spectra under biases. The energy distribution has a peaked structure with four peaks at ∼0.15, ∼0.5, ∼0.75, and ∼1.1 eV above the valence-band maximum (VBM). The 0.75-eV peak has the highest density of ∼1.9×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$ and is attributed to a (+/0) transition of ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. The weak 0.5-eV peak is tentatively attributed to a (++/+) transition of the ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. The 0.15- and 1.1-eV peaks that have densities of 1.3×${10}^{12}$ and 0.8×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$, respectively, are attributed to ${\mathrm{Ga}}_{\mathrm{As}}$ 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 ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. From the density of the interface states near the Fermi level, i.e., ∼1×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{eV}}^{\mathrm{-}1}$, it is shown that dφ/d${\mathrm{\chi }}_{\mathit{M}}$ (φ: barrier height in GaAs, ${\mathrm{\chi }}_{\mathit{M}}$: metal electronegativity) is 0.24, indicating that the Fermi level is pinned partly by the ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects and that fixed oxide positive charges with a density of (2–3)×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$ are present at the GaAs/oxide interface.