Structural Changes in a-Si:H Films Deposited on the Edge of Crystallinity

Using infrared, H evolution and x-ray diffraction (XRD), the structure of high H dilution, glow discharge deposited a-Si:H films 'on the edge of crystallinity' is examined. From the Si-H wag mode peak frequency and the XRD results, we postulate the existence of very small Si crystallites contained within the amorphous matrix, with the vast majority of the bonded H located on these crystallitesurfaces. Upon annealing at ramp rates of 8-15?C/min, a H evolution peak at -400?C appears, and film crystallization is observed at temperatures as low as 5OO?C,; both of which are far below those observed for a-Si:H films grown without H dilution using similar ramp rates. While the crystallite volume fraction is too small to be etected by XRD in the as-grown films, these crystallites catalyzethe crystallization of the remainder of the amorphous matrix upon moderate annealing, thus explaining the existence of the low temperature H evolution peak.