Electrical and optical properties of amorphous hydrogenated silicon prepared by reactive ion beam sputtering

Abstract

Amorphous hydrogenated silicon (a-Si:H) films have been prepared by a reactive ion beam sputtering technique under different conditions of substrate temperature (300-623 K) and hydrogen to argon flow ratios (0-12/1). Infrared absorption spectra of the films show that monohydride (Si-H) bonding is preferred at low deposition temperatures and increasing temperature leads to the formation of both mono- and dihydride configurations. Electrical and optical properties of the films are sensitively dependent on deposition parameters. Deposition conditions have been optimized to obtain films with low conductivity (10^-10 Ω^-1cm^-1) and high activation energy (0.7 eV) exhibiting extended state transport over a wide temperature range and a large gain in photoconductivity. The optical gap can be varied from 1.4 to 1.9 eV on changing the deposition conditions. A mixed extended state and hopping conduction is observed in high conductivity (10^-5 Ω^-1cm^-1) hydrogen rich (≥20 at.%) films deposited at lower temperatures (500 K) and those with less hydrogen (≤4 at.%) deposited at 573 K. These observations are attributed to the large gap state density originating from Si:H complexes in H₂ rich films and unsaturated bonds in poorly hydrogenated material.