Structural properties of hot wire a-Si : H films deposited at rates in excess of 100 A/s

The structure of a-Si:H, deposited at rates in excess of 100 Angstrom /s by the hot wire chemical vapor deposition technique, has been examined by x-r ay diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ra y scattering (SAXS). The films examined in this study were chosen to have r oughly the same bonded H content C-H as probed by infrared spectroscopy. As the film deposition rate R-d is increased from 5 to > 140 Angstrom /s, we find that the short range order (from Raman), the medium range order (from XRD), and the peak position of the H evolution peak are invariant with resp ect to deposition rate, and exhibit structure consistent with a state-of-th e-art, compact a-Si:H material deposited at low deposition rates. The only exception to this behavior is the SAXS signal, which increases by a factor of similar to 100 over that for our best, low H content films deposited at similar to5 Angstrom /s. We discuss the invariance of the short and medium range order in terms of growth models available in the literature, and rela te changes in the film electronic structure (Urbach edge, as-grown defect d ensity) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus R-d, measured after light soaking, and discuss possible reasons why the increase in the microvoid density apparen tly does not play a role in the Staebler-Wronski effect for this type of ma terial. (C) 2001 American Institute of Physics.