ESR and electrical properties of P-doped microcrystalline Si

Abstract

The dependences on phosphorus doping of ESR, conductivity, X-ray diffraction and hydrogen vibrational spectra have been investigated for microcrystalline Si films prepared by a new glow-discharge decomposition method where the substrate is placed in a heated plasma gas. The results are compared with those for amorphous Si : H and polycrystalline Si films. A higher deposition rate of 80–160 Å min⁻¹ and larger crystallite sizes of 150–250 Å have been found than in other methods of preparation. The morphology of an amorphous phase in the microcrystalline film is different from that in an amorphous Si : H film, and the width of the conduction band tail-states in the amorphous phase portion is considerably narrower. A large conductivity in the P-doped microcrystalline films is interpreted as arising from an enhanced upward shift of the Fermi level permitted by the reduction in the tail-state width. A strong correlation between the conductivity and hydrogen bonded in SiH₂ groups was found, the conductivity being smaller in films with high hydrogen contents. The conductivity of microcrystalline films with low hydrogen contents is analysed in terms of a random mixture of crystallites and amorphous phase regions. From ESR measurements, the electron mobility in the crystallites was found to be similar to that in single-crystal Si.