Methane as a novel doping precursor for deposition of highly conductive ZnO thin films by magnetron sputtering

ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon and argon with methane as reactive gas. It is found that growth morphology and electronic properties of the films are strongly affected by adding of methane to argon during the deposition process. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band and quenching of deep level emission in the visible spectral range. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Unexpectedly, the analysis of the chemical composition showed no carbon incorporated from methane. Therefore, modification effects were assigned to hydrogen incorporation. However, the direct comparison of resistivity of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of the methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. This advantage of the methane is discussed and assigned to specific surface chemistry of Zn–O–C–H system that enhances the formation of shallow donor defects during plasma assisted deposition process.