Nature and densities of gap states in a-Si:H and a-SiC:H obtained from the quantitative analysis of photoconductivity

The nature, distribution, and densities of midgap states in solar-cell-grade intrinsic hydrogenated amorphous silicon (a-Si:H) and hydrogenated silicon carbide (a-SiC:H) have been investigated using sub-bandgap photoconductivity and steady-state photoconductivity measurements. The sub-bandgap optical absorption was obtained by both constant photocurrent-method (CPM) and dual beam photoconductivity (DBP) techniques, and the experimental results were analyzed using detailed numerical modeling based on the Rose-Simmons-Taylor theory. The densities, energy distribution, and carrier capture cross-sections of midgap states were obtained from iterative procedure for the best fits of both sub-bandgap absorption and photoconductivities for the a-Si:H and a-SiC:H materials