Effect of Reduction Annealing on the Structural and Electrical Properties of α-MoO₃ Thin Films

Two-Dimensional Layered Molybdenum oxide (α-MoO₃) is gaining significant research interest due to its tuneable bandgap and diverse structural, chemical, electrical, and optical properties which are greatly influenced by the various growth parameters and synthesis. In this work, we report the effect of reduction-annealing on the structural and electrical properties of few layers of MoO₃ thin films on Si/SiO₂ substrate synthesized by Pulsed Laser Deposition method under a vacuum pressure of 10^-4 mbar. The structural properties of MoO₃ films were analysed under different annealing conditions using X-ray diffraction. The films have nanocrystalline structure with a preferred orientation along (0 2 0) direction. The sample annealed for 10 hours shows the formation of highly crystalline orthorhombic α-MoO₃ with prominent peak shifts indicating reduction in unit cell volume. Field emission scanning electron microscopy and energy disruptive spectroscopy provide a comparative analysis of the detailed microstructures of the films and their elemental composition. Raman spectroscopy revealed the formation of the orthorhombic α-MoO₃ layered structure, indicated by the characteristic peaks at 667, 820, and 995 cm^-1 for the O-Mo-O and the Mo=O stretch vibrational modes respectively. UV-Vis spectroscopy measurements indicated that the energy band gap of the MoO₃ films was approximately 3.25 eV. Reduction annealing introduced oxygen vacancies, leading to an increase in the electrical conductivity of MoO₃ to the order of 10^-4 Ω^-1 cm^-1. Nevertheless, preliminary FET characteristics measurements, including<i> I_DS</i> vs <i>V_DS</i> at various gate voltages, demonstrate that the samples retained their semiconducting behaviour.