Observation of improved structural ordering in low H content, hot wire deposited a-Si:H

We present the results of X-ray diffraction measurements on a series of device quality hot wire (HW) deposited a-Si:H films in which we vary only the substrate temperature of the growing film, which decreases the bonded from H content in a systematic fashion. By increasing the substrate temperature to similar to 375 degrees C, where we deposit our low H content (C-H) HW films which exhibit a reduced Staebler-Wronski effect, the width of the first peak in the X-ray diffraction pattern narrows noticeably. We interpret this narrowing to be the first indication of improved medium range ordering in our low C-H, device quality HW a-Si:H. We note in addition that measurements of the bond angle deviation, obtained from Raman measurements of the half width of the Si-Si TO phonon mode on the same samples, do not show this same evidence of improved ordering as the substrate temperature is increased. We discuss these differences in the context of sample annealing experiments designed to effuse H from the region of the sample probed by the surface sensitive Raman technique, while leaving the bulk of the material, which is sampled by the X-ray beam, largely unaffected.