Molarity-induced interfacial barrier engineering of HfO2 thin films for high-performance Cu/HfO2/n-Si MIS Schottky photodiodes

High-performance metal–insulator–semiconductor (MIS) photodiodes require dielectric interfacial layers with excellent structural quality, low defect density and efficient carrier transport. In this work, hafnium dioxide ( HfO 2 ) high-k dielectric thin films were deposited on n-type silicon substrates using the low-cost Jet Nebulizer Spray Pyrolysis (JNSP) technique by systematically varying the precursor molarity from 0.1 to 0.4 M. The influence of precursor concentration on the structural, morphological, optical, compositional and electrical properties of the HfO 2 thin films was comprehensively investigated to establish the relationship between interfacial layer quality and photodiode performance. X-ray diffraction analysis confirmed the formation of monoclinic HfO 2 with improved crystallinity and preferred (111) orientation at higher precursor molarities. Field-emission scanning electron microscopy and atomic force microscopy revealed enhanced grain growth, improved surface compactness and controlled surface roughness with increasing precursor concentration, although localized microcracks were observed at the highest molarity. X-ray photoelectron spectroscopy verified the formation of Hf–O chemical bonds together with a small contribution from surface hydroxyl species, while energy-dispersive X-ray spectroscopy confirmed successful incorporation of hafnium and oxygen within the deposited films. Optical studies revealed effective optical bandgap values ranging from 3.78 to 3.90 eV, attributed to defect-related localized states commonly observed in solution-processed oxide thin films. Electrical characterization of the fabricated Cu/ HfO 2 /n-Si MIS Schottky photodiodes demonstrated significant enhancement in interfacial barrier engineering, with the barrier height increasing to 0.70 eV and a substantial reduction in saturation current for the optimized device. Under ultraviolet illumination, the optimized photodiode exhibited a photosensitivity of 385.91% and a specific detectivity approaching 1 × 10 12 Jones, indicating excellent ultraviolet photodetection capability. The improved device performance is attributed to enhanced interface quality, reduced defect-assisted recombination and optimized carrier transport resulting from precursor molarity engineering. These findings demonstrate that precursor molarity provides an effective and scalable approach for tailoring Hf O 2 interfacial layers for high-performance MIS photodiodes and other solution-processed optoelectronic devices.