Recent developments in hot wire amorphous silicon

We present measurements of low temperature internal friction (Q(-1)) of amorphous silicon (a-Si) films designed to probe how their structure and formation affect low temperature vibrational properties. All a-Si films, whether produced by e-beam evaporation, sputtering, Si self-ion implantation, or chemical vapor deposition (CVD) show the well-known temperature-independent plateau (Q(0)(-1)) common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H) with about 1 at.% H produced by hot wire CVD; however, the internal friction is nearly three orders of magnitude less than any known amorphous material. For this material we find that Q(-1) depends on H concentration (C(H)), and on deposition conditions. For C(H) > 2 at.%, both a peak and a sharp transitional feature appear in Q(-1) between 5 and 40 K. We identify the feature as H(2), presumably in microvoids, undergoing a phase transition at the freezing point. (C) 1998 Elsevier Science B.V. All rights reserved.