Optimizing the thermal annealing temperature: technological route for tuning the photo-detecting property of p-CuO thin films grown by chemical bath deposition method

In the current work, CuO thin films (~ 110 nm) are grown by employing chemical bath deposition (CBD) method on Si substrate for fabricating the p-CuO/n-Si heterojunction photodetectors. The as-grown films are annealed at 250, 550 and 850 °C for 10 min in Ar ambient for tuning optoelectronic properties of the as-grown CuO thin films. Comparative study on systematic annealing of the film within 250–550 °C indicates a morphological change of the as-grown CuO film to nano-fiber type with its chemical composition remaining unchanged. A variation of refractive index and dielectric constant in the range of 2.65–2.93 and 7.2–9.7, and a change of absorption coefficient and bandgap from 1.33 × 10⁵ to 6.06 × 10⁵ cm^− 1 and 1.5 to 2.16 eV have been observed. The current–voltage characteristics both in dark and illuminated conditions suggest that the annealing of CuO film at 550 °C provides the best performance in terms of photo-to-dark current ratio and photoresponsivity. A respective enhancement of 5.07 and 10% for the photo-to-dark ratio and photoresponsivity has been observed for the 550 °C annealed sample.