Energy distribution of interface states in the band gap of GaAs determined from x-ray photoelectron spectra under biases.

Abstract

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 \ensuremath{\sim}3.8 nm, from measurements of x-ray photoelectron spectra under biases. The energy distribution has a peaked structure with four peaks at \ensuremath{\sim}0.15, \ensuremath{\sim}0.5, \ensuremath{\sim}0.75, and \ensuremath{\sim}1.1 eV above the valence-band maximum (VBM). The 0.75-eV peak has the highest density of \ensuremath{\sim}1.9\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ 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\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 0.8\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, 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., \ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{eV}}^{\mathrm{\ensuremath{-}}1}$, it is shown that d\ensuremath{\varphi}/d${\mathrm{\ensuremath{\chi}}}_{\mathit{M}}$ (\ensuremath{\varphi}: barrier height in GaAs, ${\mathrm{\ensuremath{\chi}}}_{\mathit{M}}$: 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)\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ are present at the GaAs/oxide interface.