Properties of fluorinated glow-discharge amorphous silicon

Abstract

Amorphous silicon films were prepared by plasma decomposition of ${\mathrm{SiF}}_{4}$+${\mathrm{SiF}}_{2}$ 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 ${10}^{17}$ spins/${\mathrm{cm}}^{3}$. 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.