Abstract
The recent experimental results and current knowledge on the positron annihilation studies for a-Si and a-Si: H are reviewed. Positron annihilation measurements have been proved as useful and powerful methods to investigate vacancy-type defects and microvoids in solids, even for amorphous semiconductors. Randomness of the structure and hydrogenation for Si increase the size and the concentration of microvoids. In particular, the quadrivacancy-like microvoids can be seen in a-Si and the formation of positronium has been observed in sputtered a-Si: H. For a-Si: H prepared at high deposition rate, the substrate temperature is one of the important factors on the concentration of microvoids. The boron doping, however, scarcely affect the concentration of microvoids and spin density. Furthermore, the annealing temperature dependence of line shape parameters are different from undoped a-Si. These influences of boron doping can be attributed to the elimination of hydrogens from the structure.
