High-Bandgap a-SI:H Deposited by Concentric-Electrode rf Glow Discharge

Abstract

ABSTRACTHydrogenated amorphous silicon (a-Si:H) with Tauc's optical bandgap (Eopt) between 1.7 and 2.1 eV was deposited at room-temperature by concentric-electrode plasma-enhanced chemical vapor deposition (CE-PECVD). The variation of Eopt was achieved by varying the flow of silane, without hydrogen dilution. The increase in Eopt results from an increase in the hydrogen concentration in the film from 7 to 15%. The photoconductivity shows a monotonie decrease with increasing Eopt and is 10'-7 Scnr-1 for the 2.1 eV sample. The Urbach energy (Eu) is observed to increase sharply with increasing Eopt, while the subgap defect (Ns) density remains approximately constant.