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 {~}20 A{}. 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.
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He et al. (1986) studied this question.
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