Structure changes by annealing and doping of a-Si:H prepared at high deposition rate studied by means of positron annihilation

Abstract

Doppler broadening measurements of γ-ray spectrum on the positron annihilation (DOBPA) have been applied to a-Si:H prepared at high deposition rate in order to explore vacancy-like microvoids. The influences of annealing and/or doping to the concentration of microvoids have been investigated. The lineshape parameters in DOBPA for the annealing show three regions for the annealing temperature. They are constant until 350 °C, slowly increasing from 350 °C to 500 °C, and then steeply decreasing until crystallization temperature. These correspond to the change in the concentration of microvoids. However, for boron-doped a-Si:H, the constant region disappears. The doping of boron itself increases the concentration of microvoids, but little dependence on the amount of boron is seen. Further, no definite evidence for positronium formation could be pointed out for these samples even in deconvoluted spectra, but the electron momentum distribution increases at about 2mc=2 × 10 −3 presumably resulting from the formation of Si-H 2 bonds near microvoids.