Positron-annihilation study of voids in<i>a</i>-Si and<i>a</i>-Si:H

Abstract

Angular correlation of positron-electron annihilation radiation (ACAR) experiments and positron-lifetime measurements have been performed in a-Si and a-Si:H films as a function of temperature. Positronium formation in microvoids is observed in a-Si:H, but not in a-Si. From the width of the narrow positronium ACAR components we estimate the average diameter of the microvoids to be \ensuremath{\sim}20 A\r{}. A complex temperature dependence of the positron and positronium lifetimes is obtained and is discussed in terms of temperature-dependent positron trapping in various sites and in terms of hydrogen detrapping from dangling bonds.