Influence of Hf- and multi-rare earth introduction on the photo-transport properties of ZnO thin films deposited on Si by magnetron sputtering and post-annealed

Abstract

Emerging evidence suggests that doped ZnO is one of the serious candidates for next-generation electronic devices because of its abundance in Earth, its nontoxicity, biocompatibility, and affordability, thus motivating many research efforts. Progress includes yet-undiscovered potential in simultaneous codoping ZnO with two or even more elements. Multidoping ZnO with rare-earth (RE) elements and Hf can induce synergistic effects that exceed individual dopant contributions. The concurrent presence of RE3+ and Hf4+ likely establishes a self-compensating defect equilibrium that suppresses oxygen vacancies and zinc interstitials, improving crystallinity and minimizing nonradiative recombination. Using this approach, new pathways for exploration of novel optoelectronic properties and applications can be provided. Meanwhile, most existing studies focus on singly doped or codoped ZnO systems, suggesting that the broader potential of multidoping remains largely unexplored. Although codoping has demonstrated notable improvements in carrier mobility, optical transparency, and defect control through compensating mechanisms between donor and acceptor ions, multidoping introduces an additional degree of freedom in tailoring material properties. Therefore, a deeper investigation of multidoped ZnO could uncover new pathways to optimize its electronic, optical, and catalytic functionalities. In this study, we show that hafnium and multi-rare earth ion implantation and post-annealing of ZnO thin films deposited on Si by magnetron sputtering enables control over the photo-transport properties of the films. Thus, their electrical resistivity can be reduced by about 50 times by multidoping. Moreover, the photoluminescence (PL) and surface photovoltage (SPV) measurements of the films revealed that multiply ion-implanted doping using Hf and different rare-earth elements, such as Nd, Ho, Er, Sm, and Tm, is beneficial for enhancing the PL intensity, slowing down the SPV rise, and speeding up the SPV decay. The signatures of the oxygen and zinc vacancies as well as an ionized local energy level formed by Hf in the modified photo-transport properties of ZnO films are observed. These results are relevant for the development of advanced optoelectronic and photonic devices that utilize zinc and hafnium oxides. Particular emphasis was placed on exploring the potential of the multidoped ZnO layers for ultraviolet photodetection applications.