Fabrication of narrow-band-gap hydrogenated amorphous silicon by chemical annealing

Abstract

Hydrogenated amorphous silicon films with optical band gaps narrower than 1.7 eV have been prepared by a chemical annealing process involving the sequential deposition of 10–30 Å of amorphous silicon followed by a plasma treatment, hydrogen and hydrogen–argon plasma treatments were investigated. Thick homogeneous films were built up by repeating the sequence many times. The formation of microcrystalline structure could be completely suppressed by the proper choice of the substrate temperature and hydrogen–argon mixture. Argon radical impingement results in hydrogen abstraction from the growth surface resulting in films with hydrogen contents as low as 3 at. %. These low hydrogen content films had a correspondingly low optical band gap of ∼1.6 eV. Raman spectra analysis indicates that the silicon–silicon bonding environment is independent of the optical band gap. However, the optical band gap is very sensitive to the content and type of hydrogenated structure present in the material. Analysis of the electronic transport indicates that these films have uniformly good transport properties.