Mobility improvement of Zn1-xMgxO:Al prepared under room temperature by co-sputtering through optimizations of Al and Mg contents

Abstract

ZnO:Al (AZO) and (Zn,Mg)O:Al (AZMO) films with several Al and Mg contents were deposited by radio frequency co-sputtering process under a room temperature (25 °C). The effects of Al and Mg contents on optical and electrical properties of the AZO and AZMO films were investigated for the suitability of the transparent conductive oxide (TCO) application in optoelectronic devices, requiring low resistivity and high transparency through the enhanced mobility. It is determined that Hall mobility of the AZO is increased, and its carrier concentration is decreased with an almost constant resistivity under the decreased Al content from about 1.7 to 0.3 at.%. The AZO film with the decreased Al content to about 0.6 at.% possesses the enhanced Hall mobility to 32.1 cm2/Vs and the reduced free-carrier absorption, which is suitable for the TCO application with its low resistivity of 5.6 × 10−4 Ω cm. It is also noted that optical bandgap energy (Eg) of the AZO films is increased with the increased Al content due to a Burstein-Moss shift. Moreover, the Mg addition into the AZMO films yields the increase in their Eg and the decrease in the free-carrier absorption under the same Al content. The resistivity of about 2.5 × 10−3 Ω cm by enhancing Hall mobility is consequently obtained in the AZMO films with the Mg content range of 0.06–0.10 with the decreased free-carrier absorption for the TCO application.