Oxygen effects on hopping transport in polycrystalline tungsten disulfide transistors via laser-assisted doping

Abstract

Tungsten disulfide (WS2), a transition metal dichalcogenide (TMD), is known for its unique optoelectronic properties, making it ideal for thin-film electronics. However, achieving the necessary improvements for practical applications requires precise control over the material's electrical properties. Annealing and chemical doping are crucial in manufacturing electronic devices to modify material properties and enhance performance, though controlled doping in TMDs is challenging. This study demonstrates controlled oxygen doping of WS₂ thin films via continuous wave laser annealing through an aluminum oxide (Al2O3) top layer, which also serves as the gate dielectric for WS₂-based top-gated transistors. The WS2 thin film was synthesized using radio-frequency sputtering and sulfurization in chemical vapor deposition, forming a tri-layer structure. Electrical characteristics of the WS₂-based thin-film transistor were assessed before and after laser annealing. X-ray photoelectron spectroscopy indicated a gradual increase in oxygen content within the WS₂ film and a corresponding decline in the Al2O3 layer, suggesting oxygen diffusion from Al2O3 into WS2 during laser processing. Post-treatment analysis revealed an increase in carrier concentration and a substantial reduction in channel resistance from 2485.6 GΩ to 25.4 GΩ (a 98.98 % decrease). Furthermore, systematic transport studies demonstrated that oxygen transfer from Al2O3 to WS2 film reduces the activation energy for hopping and facilitates the thermally activated hopping motion. Continuous wave laser annealing proves to be a promising, straightforward technique to enhance the performance and longevity of fully fabricated WS2-based devices, ensuring reliable and efficient operation. © 2025 Elsevier B.V.