Photoconductivity of DLC film deposited by pulsed discharge plasma CVD

Abstract

DLC films were deposited by a new pulsed DC discharge plasma chemical vapour deposition (CVD) using hydrogen and methane gas mixture. When methane concentration (Cm) i.e. CH 4/(H 2 + CH 4) was increased from 3 to 40%, the graphitization of the carbon film increases as evident from Raman study. When Cm was increased to 30%, DLC film shows photoconducting property. The white light photoconductivity ( S = I l/ I d, where I l is light current and I d is dark current) measured with solar simulator under AM 1.5 condition was approximately 20 at room temperature. The photoconductivity was not clear when Cm was lower than 20%. ESR measurements also show that the electron spin density was slightly decreased with decreasing concentration of methane. Thus we can conclude here that at higher concentrations of methane at 30%, Sp 2 content of the film increases and the DLC film becomes photoconducting.