On the nature of doping effect of methane in ZnO thin films deposited by RF-magnetron sputtering

A comparative study of the effects of methane and hydrogen as reactive agents on the structural, optical, and electrical properties of ZnO thin films deposited by magnetron sputtering has been performed. The research was aimed at the identification of the nature of the previously reported strong n-type doping effect of methane. To that end, the impact of carbon and hydrogen released by the plasma decomposition of methane on the properties of ZnO films was compared with the impact of molecular hydrogen intentionally added to argon. Both methane and hydrogen caused strong enhancement of n-type conductivity in ZnO films; however, the doping effect of methane was found to be about one order of magnitude larger. The main structural effect of methane was the loss of preferential orientation and a decrease in the size of ZnO crystallites. Room-temperature photoluminescence of these films exhibited a strongly reduced green-yellow emission band in the visible spectral range accompanied by the development of a specific blue emission band. The hydrogen concentration in the ZnO films deposited using methane examined by secondary ion mass spectroscopy was found to be significantly larger than that in the films deposited using pure molecular hydrogen, which is suggested to be one of the reasons for the superior n-type doping efficiency of methane in comparison with molecular hydrogen. The enhanced structural disorder caused by methane is suggested as another contribution to the doping effect of methane.

Automated summary

A study comparing the effects of methane and hydrogen on the properties of ZnO thin films deposited by magnetron sputtering has revealed that methane has a significantly larger n-type doping effect than hydrogen. Methane causes changes in the film's structure, including the loss of preferential orientation and a decrease in crystallite size. The photoluminescence of these films also shows a decrease in the green-yellow emission band and the development of a specific blue emission band.