Electron-Paramagnetic-Resonance Study of Clean and Oxygen-Exposed Surfaces of GaAs, AlSb, and Other III-V Compounds

Abstract

Clean surfaces of $p$-type GaP, GaAs, GaSb, and InAs and $n$-type GaAs, AlSb, and GaSb have been prepared by crushing in ultrahigh vacuum (${10}^{-9\mathrm{}}$ Torr) and measured by the electron-paramagnetic-resonance technique at room temperature and 77°K. A small clean-surface signal was found. When oxygen was adsorbed at 77°K, a new signal was found, due to $\mathrm{O}_2^{}{}_{}{}^{-}$ ions. In the case of AlSb, hyperfine structure was resolved. A complete analysis was carried out without the usual restriction of setting the $\overleftrightarrow{\mathrm{A}}$ (hyperfine) and $\overleftrightarrow{\mathrm{g}}$ tensors parallel. Parameters were checked by computer simulations of the spectra. About 5% of the wave function of the unpaired electron on the $\mathrm{O}_2^{}{}_{}{}^{-}$ molecule is localized on the Al atom. The unfilled (dangling) orbital of this surface atom is found to be over 90% $p$ type. This provides, apparently, the first experimental determination of a clean-semiconductor-surface wave function. A model of the (110) surface of a III-V compound semiconductor is proposed. The group-V atom dangling bond contains an electron pair in a $p$ orbital, while the group-III atom dangling bond is a largely empty $p$ orbital. In-surface bonds are largely $s{p}^2$. Parameters for the clean-surface signal on GaAs and GaSb are $g=2.0038\mathrm{}\pm 0.0004$, width 10 ± 1 G, corresponding to about 4 × ${10}^{11}$ spins ${\mathrm{cm}}^{-2\mathrm{}}$, reduced by about 30% after exposure to air. For the $\mathrm{O}_2^{}{}_{}{}^{-}$ signal on GaAs $g_{\parallel }=2.036\mathrm{}$, $g_{\perp }=2.007\mathrm{}$, and on AlSb $g_{\parallel }=2.041\mathrm{}$, $g_{\perp }=2.005\mathrm{}$.