LOW-TEMPERATURE POSITRON TRANSPORT IN SEMIINSULATING GAAS

Positron diffusion and drift in semi-insulating (SI) GaAs in the tempe rature range of 50-309 K were studied by the slow-positron beam techni que. Both the temperature-dependent positron diffusion coefficient and positron mobility were measured independently using the method report ed recently [Y. Y. Shan et al., Phys. Rev. B 54, 1982 (1996)]. The exp erimental results are consistent with the Einstein relation. The diffu sion coefficient and mobility approximately follow D+(T) = 9400T(-beta ) cm(2) s(-1), and mu(+)(T) = 10(8) x T-sigma cm(2) V-1 s(-1), with be ta = 1.5+/-0.1, and sigma = 2.5+/-0.2, respectively in the temperature range of 50-300 K. The results are consistent with scattering from op tical-phonon modes as the dominant scattering process for positron tra nsport in GaAs (SI) in this temperature range. No trapped positron sta tes were observed to 50 K.