Redox-Driven Modulation of Optoelectronic Performance in Dy-Doped MoO₃ Thin Films

Molybdenum trioxide (MoO₃) thin films have been gaining interest in research for its optoelectronic and photocatalytic applications. It is mainly because of their tunable bandgap and structural versatility. In this study we analyze the structural, optical and electrical properties of 5% Dysprosium (Dy)-doped MoO₃ thin films. The films were synthesized through Pulsed Laser Deposition (PLD) technique under a vacuum pressure of 10⁻⁴ mbar on Si/SiO₂ substrates. The films were annealed in H₂/Ar (5%/95%) atmosphere for different durations (20 min, 40 min, 2 h). Orthorhombic α-MoO₃ phase was confirmed by X-ray diffraction (XRD) analysis. It also revealed reducing crystallite sizes due to Dy incorporation inducing lattice distortion. Longer annealing time shifted the XRD peaks, which indicates unit cell contraction because of Oxygen vacancy formation. Raman spectroscopy identified characteristic Mo-O vibrational stretching  modes at 666 cm⁻¹ and bending modes at 818 cm⁻¹. Intensity reductions were observed due to oxygen deficiency. UV-Vis spectroscopy demonstrated bandgap reduction from 3.25 eV to 2.85 eV after 2 h annealing. Reduction annealing facilitates the formation of oxygen vacancies, thereby modulating carrier concentration and resulting in a significant improvement in electrical conductivity by several orders of magnitude. Despite this notable increase in conductivity, preliminary field-effect transistor (FET) measurements indicate the material retains its semiconducting behavior and further investigations are underway. Photoluminescence spectra revealed Dy³⁺-related emissions at 480 nm and 575 nm, with quenching effects observed at longer annealing times due to non-radiative recombination at defect sites. These findings demonstrate that controlled reduction annealing enables precise tuning of MoO₃:Dy's optoelectronic properties for applications in nanoelectronics and optoelectronic applications.