Local Mode Absorption in Compensated Silicon-Doped Gallium Arsenide

Infrared-active localized vibrational modes in lithium- and copper-compensated silicon-doped GaAs are reported. A number of absorption peaks due to both Si and Li are seen at liquid-nitrogen temperature. The local mode of the Si donor, SiGa, occurs at ν=384 cm−1; the Si acceptor, SiAs, at 399 cm−1. Two bands at 374 and 393 cm−1, along with a component of the 384-cm−1 band, are tentatively identified as the SiGa bands split by a Li (or Cu) acceptor. The three corresponding Li bands are seen near 450 cm−1 with 7Li and near 480 cm−1 with 6Li. For Li(Cu)-Si-doped GaAs a weak coupling model between Si-Li or Si-Cu ion pairs is proposed. This model has been previously proposed for Li-B-doped Si. Si concentration studies indicate that the strengths of the SiGa 384-cm−1 and SiAs 399-cm−1 bands are related more closely to the total Si concentration than to the carrier concentration. A number of additional and, at present, unexplained peaks are also observed.