Photoemission and photoyield of amorphous Si films

We have studied the electronic structure of in situ sputtered amorphous Si (a-Si) and hydrogenated amorphous Si (a-Si: H) films with the use of angle-integrated photoemission with synchrotron radiation. The valence-band emission gives evidence for the presence of Si---H---H---Si broken-bond configurations in the film. Combining Si $2p$ core-level photoemission measurements with photoabsorption (photoyield) studies of the Si $2p$ edge, we have also followed the evolution of the band gap with sample preparation and annealing. The band gap decreases with higher annealing temperatures, and the hydrogenated films initially have a 0.3-eV-larger band gap than does a-Si.