The microstructure and optical properties of crystallized hydrogenated silicon films prepared by very high frequency glow discharge

A series of nc-Si:H films with different crystalline volume fractions have been deposited by very high frequency glow discharge in a plasma with a silane concentration [SiH4]/([SiH4] + [H-2]) varying from 2% to 10%. The nc-Si:H films have been characterized by Raman spectroscopy, XRD diffraction, and UV-vis-near infrared spectrophotometer. The deposition rate increases nearly linear with increasing the silane concentration while the crystalline volume fraction decrease from 58% to 12%. The refractive index and the absorption of the samples were obtained through a modified four-layer-medium transmission model based on the envelope method. It was found that the refractive indices and absorption coefficient increase with increasing silane concentration. Compared to the films deposited using conventional RF-PECVD with excitation frequency of 13.56 MHz, the samples prepared by very high frequency glow discharge have higher absorption coefficients, which is due to its better compactness and lower defect density. (C) 2011 Elsevier B. V. All rights reserved.