Hydrogen roles approaching ideal electrical and optical properties for undoped and Al doped ZnO thin films

This paper distinguished hydrogen roles to improve electron mobility and carrier concentration in ZnO and Al doped ZnO sputtered films. By combining experimental evidences and theoretical results, we find out that hydrogen located at oxygen vacancy sites (H-O) is the main factor gives rise to increase simultaneously mobility and carrier concentration which has not been mentioned before. Introducing appropriate hydrogen content during sputtering not only results in crystalline relaxation but also supports doping Al into ZnO, increasing carrier concentration and electron mobility in the film. First principles calculations confirmed hydrogen substitutional stability for oxygen vacancy, significantly reducing electron conductivity effective mass and hence increasing electron mobility. In particular, 0.8% hydrogen partial pressure ratio achieved 61 cm(2)V(-1)s(-1) maximum electron mobility, optical transmittance above 82% in visible and near-infrared regions, and 2 x 10(20) cm(-3) carrier concentrations for H-Al co-doped ZnO film. These values approach ideal electrical and optical properties for transparent conducting oxide films. The presence of one maximum electron mobility was attributed to competition between increasing mobility due to restoring effective electron mass and hydrogen passivation of native defects, and decreased electron mobility due to electron-phonon scattering. (C) 2021 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.

Automated summary

This study distinguishes the roles of hydrogen in improving electron mobility and carrier concentration in ZnO and Al doped ZnO sputtered films. The experimental and theoretical results show that hydrogen located at oxygen vacancy sites is the main factor contributing to the simultaneous increase in mobility and carrier concentration. Introducing appropriate hydrogen content during sputtering not only relaxes the crystal structure, but also supports aluminum doping, resulting in increased carrier concentration and electron mobility in the film.