Composition-driven defect and interface engineering in Cu1−xZnxFe2O4 nano-interlayers for high-performance Cu/p-Si MIS Schottky ultraviolet photodiodes

Engineering defect chemistry and interface quality in nano-interlayers is an effective strategy for improving carrier transport in metal–insulator–semiconductor (MIS) photodiodes; however, the influence of composition-controlled defect engineering in ferrite nano-interlayers remains insufficiently explored. In this work, Cu 1−x Zn x Fe 2 O 4 (x = 0.2–0.8) nano-interlayers were synthesized by chemical bath deposition and employed as interfacial insulating layers in Cu/p-Si MIS Schottky photodiodes. Zn substitution was utilized as a composition-driven defect and interface engineering approach to systematically tailor the structural, optical and electronic properties of the ferrite layer. Structural and morphological analyses reveal progressive crystallinity enhancement, grain growth and reduced lattice strain with increasing Zn concentration, while optical studies demonstrate band-gap narrowing from 3.68 to 3.50 eV, promoting enhanced ultraviolet light absorption. X-ray photoelectron spectroscopy confirms oxygen-vacancy-related defect states and mixed valence species that facilitate charge transfer and improve interface quality. These interconnected structural and electronic modifications reduce carrier trapping and recombination, leading to lower ideality factors and enhanced barrier homogeneity. Consequently, the optimized Cu/ Cu 0.2 Zn 0.8 Fe 2 O 4 /p-Si photodiode exhibits a responsivity of 65.9 mA W⁻¹, quantum efficiency of 25.5% and detectivity of 2.41 × 10¹¹ Jones under ultraviolet illumination. The present work establishes a comprehensive structure–defect–interface–performance relationship, demonstrating that composition-controlled defect engineering offers a practical design strategy for high-performance ferrite-based silicon photodiodes and other optoelectronic devices.