Surface reaction probability in hydrogenated amorphous silicon growth

We deposit hydrogenated amorphous silicon (a-Si:H) on a novel ‘‘macroscopic’’ trench substrate using both remote hollow cathode (HC) silane discharges and reactive magnetron sputter (RMS) deposition sources. Both methods produce state of the art optoelectronic quality a-Si:H. We analyze the surface coverage profiles in terms of the surface reaction probability β, using a Monte Carlo simulation to correct for particle reflection and loss. We also measure the deposited film quality as a function of position in the trench. For low power silane HC deposition, we find β=0.28±0.05, whereas for the RMS case β=0.97±0.05. In contrast to the prevailing thinking in the a-Si:H field, this result demonstrates that β is not universally correlated with film quality. We discuss the role of energetic particle bombardment in RMS that permits high quality films to be deposited despite the high precursor reactivity.