High-resolution infrared study of the neutralization of silicon donors in gallium arsenide

Abstract

High-resolution infrared spectroscopy has been used to study the effects of hydrogen and deuterium plasma passivation of silicon donors in epitaxial layers of GaAs grown by metalorganic chemical-vapor deposition (MOCVD). In addition to the lines at 896 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (1-H) and 647 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (1-D) reported by Jalil et al. two new infrared absorption lines at 1717 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (2-H) and 1248 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (2-D) which show isotope shifts from paired $^{28}\mathrm{Si}$, $^{29}\mathrm{Si}$, and $^{30}\mathrm{Si}$ are found in samples passivated by hydrogen and deuterium, respectively. It is proposed that a bond between an interstitial H atom and a ${\mathrm{Si}}_{\mathrm{Ga}{}^{+}}$ impurity is formed which includes the donor electron, creating a pair defect with ${C}_{3v}$ point-group symmetry. Line 1-H is ascribed to a doubly degenerate transverse mode and line 2-H to a nondegenerate longitudinal stretching mode of the paired hydrogen. Neutralization of the ${\mathrm{Si}}_{\mathrm{Ga}}$ donors is indicated by a reduction of the carrier concentration from 4\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ to about ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, and a corresponding reduction is observed in the strength of the localized vibrational mode (LVM) line due to isolated ${\mathrm{Si}}_{\mathrm{Ga}}$ at 384 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Two new vibrational modes of the paired silicon are predicted with a small isotope shift when H is replaced by D. So far, one mode has been observed from ${\mathrm{Si}}_{\mathrm{Ga}}$-H at 409.95 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathrm{Si}}_{\mathrm{Ga}}$-D at 409.45 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.