Hydrogen Dilution of Silane: Correlation Between the Structure and Optical Band Gap in Gd a-Si:H Films

The influence of diluting SiH4 with H2 on the optical and structural properties of a-Si:H has been investigated. The major effects of the dilution are a pronounced decrease of the amount of (Si-H2)n-chains, an increase of the macroscopic density, and a decrease of the total amount of incorporated hydrogen in the films. Different models for the structure as a function of the hydrogen concentration are deduced. We also present new data on the dependence of the optical band gap Eg on the hydrogen concentration and density of the films. An important result from this work is that Eg appears to correlate with the distance between the silicon atoms, rather than with the overall hydrogen concentration.