Reduced doping efficiency of aluminium in Al-doped ZnO film: role of excess aluminium and deposition rate

Abstract

This work addresses the role of excess Al and deposition rate in reducing the doping efficiency of Al+3 cations in Al-doped ZnO (AZO) films. In this regard, AZO films were deposited on the soda lime glass substrates using co-sputtering from ceramic AZO/ZnO and metallic Al targets. Whereas power to ZnO/AZO target was kept constant, power to Al target was varied to see the effect of varying Al concentration (and deposition rate) on its doping efficiency. Here, Al doping efficiency in ZnO is found to increase initially with increasing deposition rate and Al content, beyond which it decreased because of the formation of higher AlxOy in combination with increased trapped Al in the amorphous regions of these films. Moreover, a detailed discussion on the mechanism of the deposition rate and thereby induced variation in Al doping efficiency is discussed and then related to the optoelectronic properties of these films.