Infra-red absorption and Raman scattering studies were made of the localized vibrational modes, which were due to defects that incorporated Si impurities, in p-type Si-doped GaAs. The latter had been grown by liquid phase epitaxy onto (001) planes, or by molecular beam epitaxy onto (111)A and (311)A planes. An analysis of a closely compensated liquid phase epitaxial sample indicated that an existing calibration factor for the SiAs localized vibrational mode (399/cm), which related the integrated absorption coefficient to the SiAs concentration, should be increased by 40%. Thus, an integrated absorption coefficient of 1/cm2 corresponded to a SiAs concentration of 7 x 1016/cm3. The SiAs localized vibrational mode appeared as a Fano dip in the hole absorption continuum at about 395/cm in highly doped p-type material. This was some 4/cm lower in frequency than its normal position in compensated GaAs. The electron irradiation of samples led to the progressive removal of the Fano dip and to a shift; with the emergence of the expected SiAs localized vibrational mode absorption line at 399/cm. In the case of molecular beam epitaxial material, the irradiation also generated SiGa donors, but site-switching was not detected in liquid phase epitaxial material. On the other hand, the Raman spectra of as-grown p-type samples exhibited a symmetrical peak at 395/cm, which also shifted towards 399/cm as the free carriers were removed. Molecular beam epitaxial (111)A Si-doped GaAs which was compensated by SnGa donors had the SiAs localized vibrational mode at its normal position. Following the hydrogenation of molecular beam epitaxial and liquid phase epitaxial samples, only the stretch modes which were due to H-SiAs were observed. Passivated molecular beam epitaxial (111)A GaAs which was co-doped with Si and Be exhibited stretch modes which were due to both shallow acceptors. It was concluded that only one type of acceptor (SiAs) was present in p-type Si-doped GaAs, contrary to previous suggestions. There was no evidence for the presence of SiAs pairs, or larger clusters.

M.J.Ashwin, M.R.Fahy, R.C.Newman, J.Wagner, D.A.Robbie, M.J.L.Sangster, I.Silier, E.Bauser, W.Braun, K.Ploog: Journal of Applied Physics, 1994, 76[12], 7839-49