Positron diffusion was measured in undoped and Si-doped samples, at 20 to 290K, by using positron beam techniques. The experimentally determined diffusion lengths were strongly affected by positron trapping at vacancies and negative ions in the samples. After subtracting trapping effects, the diffusion coefficient for free positrons in the lattice was obtained. The diffusion coefficient was equal to 14cm2/s at 20K and equal to 1.6cm2/s at 295K. At temperatures below 80K, it followed a T-½ law due to scattering from acoustic phonons. The diffusion coefficient between 80 and 300K decreased strongly with increasing temperature, and suggested that positron scattering from polar-optical phonons was occurring.

Low-Temperature Positron Diffusion in GaAs. T.Laine, K.Saarinen, P.Hautojärvi: Physical Review B, 2000, 62[12], 8058-63