Zinc vacancy-induced high-TC ferromagnetism and photoluminescence in group-1 alkali-metal substituted p-type ZnO thin films

Abstract

Here, we report the cation vacancy-induced room-temperature ferromagnetism (RTFM), photoluminescence (PL) and electrical properties of different group-IA alkali-metal (Li, Na, K)-doped ZnO thin films fabricated by pulse laser deposition. The experimental evidence indicates that the Zn vacancies are responsible for the visible green luminescence and RTFM in the alkali-doped ZnO films. The alkali-metal ions are found to have a crucial role in the formation and stabilization of the Zn vacancies and also to introduce the p-type conductivity to mediate the long-range ferromagnetic interaction in the films. The Li-doped ZnO films are found to exhibit the most intense green luminescence due to the presence of a large concentration of Zn vacancies and consequently, they exhibited the strongest RTFM with the highest saturation moment (M_S) and Curie temperature (T_C). The concentration of the Zn vacancy as well as the carrier (hole) density of the alkali-doped ZnO films decrease gradually when the alkali-dopants are varied from Li to Na, then to K, resulting in a decrease in both the M_S and T_C. This study demonstrates that the alkali elements are promising dopants to stabilize and tune high temperature FM in ZnO which can be an exciting way to prepare a new class of ZnO-based magnetic semiconductors.