A study of hydrogenated amorphous silicon deposited by rf glow discharge in silane-hydrogen mixtures

Abstract

The rf glow discharge deposition of hydrogenated amorphous silicon from silane-hydrogen mixtures has been studied as a function of silane fraction. Discharge processes were investigated using optical emission spectroscopy and mass spectrometry. The deposited films were characterized using UV and IR spectroscopy, dark conductivity, and photoconductivity. The dilution of silane in hydrogen resulted in an increase in deposition rate by as much as an order of magnitude over the rate for pure silane, for constant values of total flow rate, pressure, substrate temperature, and rf power. The dependence of deposition rate on silane fraction is attributed to changes in the electron energy distribution in the plasma. The hydrogen content and optical gap of the films are independent of the silane fraction. Photoconductivity values, corrected for slight variations of the Fermi level, increase with silane dilution.