High-temperature positron diffusion in Si, GaAs, and Ge

Positron diffusion coefficients have been determined in Si, GaAs, and Ge in the temperature range 130–1000 K using the positron-beam technique. The diffusion coefficients at 300 K in Si, GaAs, and Ge are 2.3(2), 1.6(2), and 1–2 ${\mathrm{cm}}^2$/s, respectively. In Si, the diffusion coefficient has the temperature dependence ${\mathit{T}}^{\mathrm{-}1/2}$ from 30 to 500 K [combined with the experiment of Mäkinen et al., Phys. Rev. B 43, 12 114 (1991)], consistent with positron scattering from longitudinal acoustic phonons. At T>500 K the diffusion coefficients are lower than extrapolated from the ${\mathit{T}}^{\mathrm{-}1/2}$ dependence indicating the onset of optical-phonon scattering. The first-order optical deformation-potential parameter is estimated to be 11 eV. Positron scattering from ionized impurities is observed in heavily doped n-type Si. In Ge, the temperature dependence of the diffusion coefficient is ${\mathit{T}}^{\mathrm{-}1/2}$ above 500 K. At room temperature the experiment yields an abnormally high diffusion length which is attributed to space-charge effects. In GaAs the diffusion coefficient is only weakly dependent on temperature from 300 to 800 K, which is interpreted to be due to positron scattering from both acoustic- and polar-optical-phonon modes. The agreement with theory is good using the theoretical deformation-potential parameters and the positron effective masses ${\mathit{m}}^{\mathrm{*}}$=1.3${\mathit{m}}_{\mathit{e}}$-1.6${\mathit{m}}_{\mathit{e}}$ in Si, GaAs, and Ge.