Properties of fluorinated glow-discharge amorphous silicon

Amorphous silicon films were prepared by plasma decomposition of SiF₄+SiF₂ gas. Structural analysis, electronic-transport-property measurements, optical-property measurements, and electron-spin-resonance measurements were performed as a function of deposition and annealing temperature. Hydrogenated amorphous silicon (a-Si:H) samples were prepared in a separate identical reactor under similar plasma conditions for reference. The results indicate that compensation of dangling bonds by fluorine alone can be obtained, yielding ESR values of the order of 10¹⁷ spins/cm³. The a-Si:F films can be doped. The dark conductivity of a-Si:F increases with spin density, but the photoconductivity is low and independent of the spin density. The differences between a-Si:F and a-Si:H are interpreted in terms of the different diffusivity and bond strength of fluorine and hydrogen in the a-Si matrix. These differences result in a larger density of tail states in a-Si:F relative to a-Si:H samples of equal spin densities.