Enhancement of Hopping Transport in Polycrystalline WS₂ via Gate-Induced Oxygen Diffusion from Laser Digital Annealing

Polycrystalline WS₂, as a transition metal dichalcogenide, possesses unique optoelectronic properties, making it well-suited for thin-film electronic devices. However, precise control of the material's electrical properties remains challenging due to the structural limitations of thin WS₂ films, and traditional methods such as thermal annealing and chemical doping often face difficulties achieving uniform and damage-free modification.
In this study, we propose a novel approach to enhance the electrical properties of polycrystalline WS₂ through the deposition of Al₂O₃, serving as the gate dielectric for top-gated WS₂-based transistors, followed by continuous wave laser annealing on the top gate area. The laser annealing process induces controlled oxygen diffusion from the Al₂O₃ top layer into the WS₂ film, effectively substituting sulfur vacancies without causing structural damage. This laser digital annealing technique significantly increases carrier concentration and dramatically reduces channel resistance from 2485.6 GΩ to 25.4 GΩ, achieving a 98.98% reduction. This improvement surpasses the limitations of conventional annealing and doping methods by providing a more targeted and uniform doping process.
To further understand the mechanism behind the observed reduction in channel resistance, low-temperature measurements (113 K – 293 K) were conducted on polycrystalline WS₂ thin-film transistors. Our analysis reveals that oxygen diffusion modifies the thermally activated hopping transport mechanism by decreasing activation energy and the density of localized states near the Fermi level, while increasing the hopping distance. This leads to a substantial enhancement in device performance and reliability.
Compared to existing doping techniques, the proposed laser annealing method offers a CMOS-compatible, non-destructive, and scalable solution for enhancing the performance of WS₂-based devices. These results suggest that continuous wave laser annealing is a promising and straightforward technique to improve the performance and longevity of WS₂ thin-film transistors, making it suitable for large-scale electronic and optoelectronic applications.

Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT) (2022M3D1A2083618) and by the Ministry of Education (2020R1A6A1A03040516).