The effect of the flow of silane on the properties of a-Si:H deposited by concentric-electrode radio frequency glow-discharge

Abstract

High band gap, device-quality, hydrogenated amorphous silicon (a-Si:H) was deposited from silane at room temperature using concentric-electrode plasma-enhanced chemical vapor deposition (CE-PECVD). Increasing the flow of silane from 15 to 99 sccm resulted in a continuous increase of the optical band gap, Eopt, from 1.7 to 2.1 eV, and changed the dominant bonding configuration from Si-H to Si-H2. The total hydrogen concentration as determined from the integrated absorption of the SiHx stretching bond increased from 7% to 15%. As Eopt varied between 1.7 and 2.1 eV, the photoconductivity, σph, decreased from 10-5 to 10-7 Ω-1 cm-1 and the dark conductivity, σd, dropped from 10-10 to 10-14 Ω-1 cm-1 (σph and σd measured at room temperature after a 1 h anneal at 200°C). These results are superior to those obtained using a-SiC:H alloys deposited under comparable conditions (i.e., without hydrogen dilution). After annealing, three different conduction paths were identified and correlate with the silicon-hydrogen bonding configuration. The photosensitivity of high band gap a-Si:H films, σph/σd, follows Slobodin's rule for a-SiGe:H alloys. High band gap a-Si:H deposited by CE-PECVD has significant potential to challenge the role of a-SiC:H as the choice material for films with 1.7 ≲ Eopt ≲ 2.1 eV.