Positron transport studies at the Au - (InP:Fe) interface

Abstract

Positron mobility and lifetime measurements have been carried out on semiinsulating Fe-doped InP samples with Au contacts used for electric field application. The lifetime measurements, with electric fields directed towards the Au-InP:Fe interface, reveal no component associated with interfacial open-volume sites and thus give no evidence of any positron mobility. The mobility measurements, made using the Doppler-shifted annihilation radiation technique, however, reveal a temperature independent positron mobility of about 20 cm 2 V −1 s −1 in the range 150-300 K. These observations, together with results from I -V analysis, are discussed with reference to two possible band-bending schemes. The first, which requires an ionized shallow donor region adjacent to the Au-InP interface, seems less plausible on a number of grounds. In the second, however, an Fe 2+ negative space charge produces an adverse diffusion barrier for positrons approaching the interface together with a non-uniform electric field in the samples capable of explaining the observed mobility results.