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

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 cm^-1 (1-H) and 647 cm^-1 (1-D) reported by Jalil et al. two new infrared absorption lines at 1717 cm^-1 (2-H) and 1248 cm^-1 (2-D) which show isotope shifts from paired ²⁸Si, ²⁹Si, and ³⁰Si are found in samples passivated by hydrogen and deuterium, respectively. It is proposed that a bond between an interstitial H atom and a Si_Ga⁺ impurity is formed which includes the donor electron, creating a pair defect with C₃ᵥ 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 SiGa donors is indicated by a reduction of the carrier concentration from 4×{}10¹⁸ cm^-3 to about 10¹⁷ cm^-3, and a corresponding reduction is observed in the strength of the localized vibrational mode (LVM) line due to isolated SiGa at 384 cm^-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 SiGa-H at 409.95 cm^-1 and SiGa-D at 409.45 cm^-1.