Effect of Bi doping level on optoelectronic functionality of CdO in Si-based heterojunctions

Abstract CdO and bismuth (Bi)-doped CdO (Bi:CdO) thin films were prepared on glass and p-Si substrates using a spin-coating technique. Energy-dispersive X-ray (EDX) spectra confirm the elemental composition of Bi-doped CdO films, revealing the presence of cadmium, oxygen, and bismuth in appropriate atomic percentages. Atomic force microscopy (AFM) analysis indicates that the surface roughness of CdO films can be effectively controlled through Bi doping. X-ray diffraction (XRD) measurements demonstrate that all CdO thin films possess a cubic CdO crystal structure. No diffraction peaks associated with Bi-related impurity phases are observed in the Bi-doped CdO patterns, indicating that Bi incorporation does not alter the CdO crystal structure. Furthermore, variations in the optical band gap ( E g ) are observed as a function of Bi doping concentration. The electrical characteristics of Al/Bi:CdO/p-Si heterojunctions with CdO thin films containing 0.0, 0.5, 1, and 2 wt% Bi were investigated using current–voltage ( I–V ) measurements under dark conditions and various illumination intensities. The results demonstrate that both the undoped and Bi-doped CdO/p-Si diodes exhibit good photodiode behavior. The photodetector achieves a detectivity of 1.15 × 10 9 Jones, while exhibiting a photoresponsivity in the 10⁻ 3 A/W range.