Positron mobility in semi-insulating 4H-SiC

Abstract

Recently, as a result of the observation of positron re-emission from crystalline 6H-SiC, it has been suggested that SiC may be a promising material for a field assisted positron moderator [1]. In this paper an attempt is made to more deeply analyze this potential application of SiC, by presenting data on the low field positron electric field drift in semi-insulating 4H-SiC as obtained using the Doppler shifted annihilation radiation technique. A low positron mobility value 3.5±3.0cm 2V -1 s -1 is found, which must be compared with values in the range 5-30cm 2V -1 s -1 obtained from positron diffusion length data. While these ranges are not incompatible, the higher values obtained from diffusion length data may indicate incomplete positron thermalization. An alternative possibility is that screening by micropipes or other defects could somehow be lowering the electric field seen by positrons in the mobility experiment.