The role of hydrogen and boron in a-SiH : B—Electronic and optical properties

Measurements of electrical conductivity and optical constants of thin films of a-SiH : B produced with varying hydrogen concentration (C_H = 0–30 at%) and boron concentration (C_B = 0.1–10 at%) are used to investigate the effects of increasing hydrogenation and doping on the density of states (DOS) of the a-Si network. There exist strong and abnormal dependences of electronic properties on C_H and C_B which correlate with increasing topological disorder of the a-Si network. For undoped films, concentrations of hydrogen up to 15 at% lead to a general decrease in the density of defect and band-tail states, a redistribution of valence band states, and a widening of the optical gap. A hydrogen content > 15 at% leads to increasing density of localized dangling-bond type states and deep-lying valence band states suggesting substantial topological disorder.