Band gap tuning of a-Si:H from 1.55 eV to 2.10 eV by intentionally promoting structural relaxation

Abstract

Substrate temperature and sequential treatments are used to prepare a-Si:H films with band gaps ranging from 1.55 to ∼2.1 eV. Low band gap materials were prepared at higher substrate temperature using a sequential process involving the deposition of thin (≲5 nm) a-Si:H layers followed by an Argon radical (and/or ion) treatment. Larger band gap materials were prepared at lower substrate temperatures using a hydrogen chemical annealing process. The series was used to determine the relationship among the deposition conditions, the opto-electronic characteristics, and the atomic bonding structures in a-Si:H. The band gap is correlated to the total di-hydride content. The local silicon–silicon bonding environments, the hydrogen, and mono-hydride content and the mono- to di-hydride ratio are not well correlated to the band gap. Electronic transport is correlated with the local silicon–silicon bonding environment, but not the di-hydride content.