FIELD-EFFECT ON POSITRON DIFFUSION IN SEMIINSULATING GAAS

An energy-tunable monoenergetic positron beam was used to study positr on diffusion in the space-charge region of an Au/GaAs(SI) (semi-insula ting) Schottky contact, where the electric field reaches similar to 10 (5) V cm(-1) by reverse biasing the diode. An analytical solution of t he time-dependent positron drift-diffusion model under an electric fie ld was obtained for the case of a semi-infinite body with a capturing boundary, and explains the experimental results well. A positron diffu sion coefficient of 1.8+/-0.2 cm(-2) s(-1), and a positron mobility of 70+/-10 cm(2) V-1 s(-1) in GaAs(SI) at 300 K, were obtained independe ntly. This result is consistent with the Einstein relation. The depend ence of the positron current density at the Au/GaAs interface on the e lectric field shows that GaAs(SI) is a possible candidate for the fabr ication of the field-assisted positron moderator.