Exploring the synergistic effects of aluminum and hydrogen impurities on high-electron-mobility sputtered-ZnO thin films

This study investigated the influence of aluminum (Al) impurity on the lattice structure, electrical, and optical properties of ZnO thin films, which were sputtered under a high vacuum environment using argon and hydrogen gases. The results revealed high electron mobility (mu) alongside a significant increase in carrier concentration (n), which deviates from the behavior typically observed in semiconductor materials. Particularly in conventional semiconductors, within the n range of 1020 cm-3, the mu exhibits a dramatic decrease with even a small increase in n. Interestingly, in this study, despite the increase in n from 2 to 3.8 x 1020 cm-3, the mu remains consistently high at around 53 cm2/Vs. Additionally, this study reveals that at an appropriate concentration, Al serves not only as a substitute for Zn to generate electrons but also as a defect passivator, similar to hydrogen. The synergistic effect of Al and hydrogen also relaxes the crystal structure, minimizing deformation and enhancing electron mobility. These effects contribute to low resistivity alongside the inherent high optical transmittance of ZnO thin films, resulting in a significantly improved figure of merit.