DISTRIBUTION OF ELECTRONIC GAP STATES IN A-SI-C-H WITH LOW-CARBON CONTENT

Measurements of steady-state photo-induced absorption (PA) were carried out on a series of a-Si:C:H samples with low carbon content at room temperature and at 50 K. Room-temperature data reveal the influence of carbon on deep defects (dangling bonds) in the energy gap as well as the energy positions of these states. At 50 K, band tails play an important role for samples with carbon concentrations below roughly 5 at. %. From these measurements the Urbach-tail parameter E(o) is determined. The resulting values can be compared with those obtained from constant photocurrent measurements (CPM) on co-deposited samples.