FABRICATION OF NARROW-BAND-GAP HYDROGENATED AMORPHOUS-SILICON BY CHEMICAL ANNEALING

Hydrogenated amorphous silicon films with optical band gaps narrower t han 1.7 eV have been prepared by a chemical annealing process involvin g the sequential deposition of 10-30 Angstrom of amorphous silicon fol lowed by a plasma treatment, hydrogen and hydrogen-argon plasma treatm ents were investigated. Thick homogeneous films were built up by repea ting the sequence many times, The formation of microcrystalline struct ure could be completely suppressed by the proper choice of the substra te temperature and hydrogen-argon mixture. Argon radical impingement r esults in hydrogen abstraction from the growth surface resulting in fi lms with hydrogen contents as low as 3 at. %. These low hydrogen conte nt films had a correspondingly low optical band gap of similar to 1.6 eV. Raman spectra analysis indicates that the silicon-silicon bonding environment is independent of the optical band gap. However, the optic al band gap is very sensitive to the content and type of hydrogenated structure present in the material. Analysis of the electronic transpor t indicates that these films have uniformly good transport properties. (C) 1998 American Institute of Physics.