Surface and bulk density of states of a-Si:H determined by CPM and total-yield photoelectron spectroscopy

The density of states (DOS) of a-Si:H and the influence of light soaking were studied with the constant photocurrent method (CPM) and total-yield photoelectron spectroscopy for films prepared at substrate temperatures between 100°C and 400°C. While by the first method information about the bulk is obtained the other yields the DOS in the surface-near region. At the surface we observed a relative to the bulk enhanced density of states as well as an enhanced influence of light soaking. In addition changes of the DOS of fresh films occur upon annealing at 190°C which can be significantly larger than the light induced effects.