Effect of Hydrogen Dilution on the Nanostructural and Electrooptical Characteristics of Hydrogenated Nanocrystalline Silicon Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition

Abstract

Nanocrystalline hydrogenated amorphous silicon (nc-Si:H) thin films were deposited on silicon wafers and glass by plasma-enhanced chemical vapor deposition. The hydrogen dilution in the precursor gases, [SiH4/H2], were varied from 1 to 0.01 with the other deposition factors kept constant. The nanocrystallite size and volume fraction increased steadily with increasing hydrogen dilution ratio in the gas from 1 to 0.01. The mean size of the nanocrystallites ranged from ∼1 to ∼7 nm. The band gap of the films varied according to the hydrogen dilution, indicating the nanostructural features of the films. Film resistivity was dependent on the crystallite size and volume fraction in the films. In particular, the resistivity of a simple P–I–N type device decreased with increasing nanocrystallite size. The increased crystallinity can be explained by the predominance of Si–H bonds in the films.