Broadband oxide-based photodetectors have attracted considerable attention owing to their stability, low cost, and potential for optoelectronic applications. In this work, a SnO \(_{2}\) /Co \(_{3}\) O \(_{4}\) /Si n-p-n heterojunction photodetector was fabricated using chemically synthesized Co \(_{3}\) O \(_{4}\) and SnO \(_{2}\) nanostructures. The novelty of this work lies in the development of a SnO \(_{2}\) /Co \(_{3}\) O \(_{4}\) /Si n-p-n heterojunction that combines n-type SnO \(_{2}\) and p-type Co \(_{3}\) O \(_{4}\) to promote efficient carrier separation and broadband visible-infrared photodetection. The X-ray diffraction patterns confirmed that the Co \(_{3}\) O \(_{4}\) nanoparticles possessed a cubic spinel structure, whereas SnO \(_{2}\) exhibited a tetragonal crystal system, with crystallite sizes of 29 and 27 nm, respectively. SEM observations revealed rod-like Co \(_{3}\) O \(_{4}\) agglomerates together with uniformly distributed SnO \(_{2}\) nanoparticles, confirming the successful formation of the oxide layers. UV–Vis spectroscopy revealed optical band gaps of 2.70 and 3.75 eV for Co \(_{3}\) O \(_{4}\) and SnO \(_{2}\) , respectively, which are larger than those of the corresponding bulk materials, confirming successful nanostructure formation. FTIR spectra showed O-H, C=O, and C-H bands in addition to the characteristic Co-O/O-Co-O and Sn-O-Sn vibrational modes. The current–voltage (I-V) characteristics of the SnO \(_{2}\) /Co \(_{3}\) O \(_{4}\) /Si heterojunction were evaluated under dark and illuminated conditions in both forward and reverse bias. The fabricated photodetector exhibited responsivities of 0.27 and 0.56 A/W in the visible and infrared regions, respectively. The external quantum efficiency and specific detectivity followed the same trend as the spectral responsivity, reaching 75.62% and 3.92 10 \(^{12}\) Jones at 450 nm, respectively. At longer wavelengths, enhanced absorption in the silicon substrate increased these values to 82.06% and 8.04 \(\times \) 10 \(^{12}\) Jones, respectively, at 850 nm. The enhanced photodetection performance is attributed to the effective SnO \(_{2}\) /Co \(_{3}\) O \(_{4}\) heterointerface, which promotes carrier separation and transport. These findings demonstrate that the proposed SnO \(_{2}\) /Co \(_{3}\) O \(_{4}\) /Si heterojunction is a promising candidate for broadband visible-infrared optoelectronic applications.
