Layer-dependent evolution in the physical properties of spin-coated cadmium oxide thin films and performance evaluation of p-Si/n-CdO/Al heterojunction diodes

This work provides a detailed investigation on the physical characteristics of spin-coated CdO thin films and the transport phenomena in p-Si/n-CdO/Al heterojunction diodes based on the number of layers. The GI-XRD studies clearly depicted the presence of the cubic CdO structure with (111) preferred orientation, signifying an improvement in crystallinity. FESEM and AFM observations disclosed that although the films were homogeneous at lower deposited layers, surface agglomeration and roughness were evident in higher deposited layers. Optical analysis depicted a marginal reduction in the band gap value up to 12 layers, followed by a slight increase, indicating modifications in the electronic structure. The XPS measurements indicated a variation in Cd²⁺ concentration, thereby indicating the presence of oxygen vacancies. The electrical analysis using the thermionic emission and Cheung models revealed that the barrier height values increased with an increased number of layers. A rectification ratio of three orders is obtained in the device at 10 layers. The results clearly signify that optimising the layers can significantly improve the performance of metal oxide-based heterojunction diodes in electronic and optoelectronic devices.