Positron mobility in Si at 300 K

Positron motion in an electric field is studied experimentally by measuring the drift length of positrons in the space-charge region of a Au-Si surface-barrier diode. An electric field of the order of 104 V/cm gives rise to a drift length from 2 to 3 m. The drift-diffusion approximation can explain positron transport up to an electric-field strength of 3×104 V/cm. At 300 K we get a positron mobility of 120±10 cm2/V s in Czochralski-grown Si ([P]=7.4×1014 cm-3), and the diffusion coefficient calculated from the Einstein relation is 3.0±0.25 cm2/s. Positron diffusion was measured without preparing a metal-semiconductor contact in high-purity floating-zone Si (104 cm) assuming the electric field can be neglected. The diffusion coefficient is 3.10±0.20 cm2/s, in good agreement with that based upon the positron mobility measured under an electric field.