Light-induced structural changes and their correlation to metastable defect creation in intrinsic hydrogenated amorphous silicon films

Abstract

Device-quality intrinsic a-Si:H films were prepared by three methods, hot-wire (HW) chemical vapor deposition (CVD), and glow-discharge (GD) CVD with and without H dilution, and show varied light-induced metastable defect creation [Staebler-Wronski effect (SWE)]. We found the following: (a) In addition to the nonuniform H distribution, the a-Si network is inhomogeneous, and the film prepared by GD is more homogeneous than the HW film. (b) The light-induced increase of Si-H stretching absorption at $\ensuremath{\sim}2000 {\mathrm{cm}}^{\ensuremath{-}1}$ is on the order of ${10}^{\ensuremath{-}2}$ in all the films, and an additional decrease at $\ensuremath{\sim}2025 {\mathrm{cm}}^{\ensuremath{-}1}$ is found in films with larger SWE. (c) The change of the compressive stress is on the order of ${10}^{\ensuremath{-}4}$ of the initial value in the HW films, which is the same order of magnitude as in GD films. Both the initial stress and light-induced volume expansion decrease with decreasing Si-H concentration. No simple correlation between the light-induced structural changes and the conductivity changes was found in the HW a-Si:H films. We describe the light-induced structural changes in conjunction with the creation of metastable defects by a two-phase model.