Effect of Depletion Region Width on Self-Powered UV–Visible Photoresponse of Cu2O-In2O3 Planar p–n Junction Photodetectors

Self-powered photodetectors have garnered significant attention due to their potential applications in optical communication, remote sensing, and imaging. This work presents p-Cu2O/n-In2O3 type-II heterojunction photodetectors via sputtering, achieving self-powered photodetection across the ultraviolet-visible spectrum. Here, Cu2O-In2O3 planar p–n junction thin films are developed with different depletion region widths (DRWs) of 1.5, 3.0, and 4.5 mm. Optical studies confirm that the In2O3 film exhibits strong ultraviolet (UV) absorbance and a wide bandgap of 3.35 eV. In contrast, the Cu2O film exhibits strong UV–visible absorbance with a narrow bandgap of 2.25 eV. Among the devices, the device with a DRW of 3.0 mm achieves higher photodetector performance, attributed to a stronger electric field and reduced charge-carrier recombination in the depletion region. Consequently, the device with a 3.0 mm DRW shows the highest responsivity (Rλ) of 4.8 mA/W, 9.4 mA/W, 13.8 mA/W, and 4.4 mA/W and detectivity (D*) of 2.14 × 1010 Jones, 4.19 × 1010 Jones, 6.15 × 1010 Jones, and 1.98 × 1010 Jones at 380, 460, 530, and 630 nm illuminations, respectively, even at lower incident optical power densities. Although the fabricated Cu2O-In2O3 p–n junction self-powered photodetector devices exhibit relatively modest figures of merit, they offer distinct advantages: self-powered operation, a broad spectral response in the UV–visible region, and stable photoresponse, highlighting their potential for low-power optoelectronic applications.