Post-deposition annealed MoO₃ film based high performance MSM UV photodetector fabricated on Si (100)

Molybdenum oxide (MoO₃) films were prepared on Si (100) at room temperature using radiofrequency (RF) magnetron sputtering technique. The films were annealed in the presence of air at different temperatures from 100 to 550 °C. The as-prepared films were amorphous as revealed by the X-ray diffraction analysis. Post-deposition annealing of MoO₃ film enhanced its crystalline structure, showing β-MoO₃ phase at 100 °C and a mixture of α-MoO₃ and β-MoO₃ phases at 300 °C. The crystallinity of α-MoO₃ improved with increasing the annealing temperature to 500 °C, however, the β-MoO₃ phase became amorphous. The film was dissolved at 550 °C as no diffraction peak of MoO₃ was detected at this temperature. The band gap of MoO₃ was evaluated through ultraviolet–visible spectroscopy. The results showed a decrease in the band gap from 3.70 to 3.39 eV with increasing the annealing temperature to 500 °C. The film with optimum crystalline quality was used to fabricate a metal-semiconductor-metal (MSM) photodetector device. The photo-detection characteristics of the film were studied after the deposition of Nickel contacts on MoO₃ using a metal mask having interdigitated electrodes. The fabricated device exhibited a high current gain and sensitivity under 365 nm UV illumination. The responsivity of the device under UV light was 0.41 A/W at 7 V. The rise and decay time of UV photodetector were 0.32 and 0.23 s respectively. These findings suggested that the MoO₃ film with dominant orthorhombic α-phase can potentially be used for the photodetector application.