Graded silicon based PECVD thin film for photovoltaic applications - art. no. 66740A

Silicon based thin film alloys are deposited using plasma enhanced chemical vapor deposition (PECVD) with silane, ammonia, and nitrous oxide as precursors with different partial pressure ratios. Numerous deposition conditions have been considered to produce films with a wide range of refractive indices. The optical properties of the films are mostly affected by hydrogen content and stoichiometry, which are characterized by means of Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) respectively. The results of spectroscopic ellipsometry measurement of the refractive index are correlated with stoichiometry extracted using XPS to enable the prediction of optical properties from process conditions. Based on the film characterization results, a graded index film is deposited to minimize the reflection loss. The optical properties of the film to be used as anti-reflection coating (ARC), i.e. the transmittance and reflectance, are measured using an optical spectrophotometer. In spite of the optical absorption in the high refractive index part of the film, it is shown that by employing a very thin layer of amorphous silicon, it is possible to reduce reflection below conventional graded index films consisting of silicon oxynitride, and still maintain the transmittance required for solar cell applications.