Localized Vibrations of Lithium Complexes in Gallium Arsenide

Infrared spectroscopy is applied to the determination of the structure of point-defect configurations in GaAs involving lithium. Lithium is self-compensating in GaAs and may be used to compensate crystals of GaAs doped with either donor or acceptor impurities. The relatively light lithium ions introduce localized vibrational modes into the crystals, and an investigation of the localized-mode spectrum gives information about the environment of the lithium impurities. Localized-mode spectra occur which have been attributed to unassociated interstitial ${\mathrm{Li}}^{+}$ ions (donors), unassociated substitutional ${\mathrm{Li}}^{-}$ ions (acceptors), and ${\mathrm{Zn}}^{-}$-${\mathrm{Li}}^{+}$, ${\mathrm{Cd}}^{-}$-${\mathrm{Li}}^{+}$, and ${\mathrm{Te}}^{+}$-${\mathrm{Li}}^{-}$ pairs. Additional spectra have been observed for which tentative explanations are offered. The ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$-${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ vibrational isotope shift has been investigated.