Crystalline NiO films by hollow-cathode plasma-enhanced atomic layer deposition: Material properties and heterojunction device performance

This study investigates the deposition of crystalline nickel oxide (NiO) thin films using hollow-cathode plasma enhanced atomic layer deposition (HCP-ALD) with an Ar/O₂ plasma mixture and nickelocene as a cost-effective precursor. Saturation studies were performed to determine the optimal deposition parameters for the films. The deposition process was conducted on n-Si and soda-lime glass substrates within a temperature range of 100–250°C, yielding films with a thickness of approximately 25–30 nm after 800 ALD cycles. The growth per cycle values were found to range between 0.29 and 0.39 Å, depending on the temperature and Ar/O₂ plasma ratio. Optical analysis revealed a bandgap energy ranging from 2.99 to 3.20 eV, and X-ray diffraction patterns confirmed the crystalline nature of the films, with a predominant (200) orientation. The refractive index and extinction coefficient were also studied, showing that increasing the deposition temperature and altering plasma conditions significantly affected the optical properties , with the film deposited at 200°C under 0/20 sccm Ar/O₂ plasma exhibiting the lowest extinction coefficient and highest refractive index , suggesting improved crystal quality. Electrical characterization of p-NiO/n-Si junctions revealed that films deposited at 200°C exhibited the highest resistivity (42.15 Ωcm), which decreased with increasing oxygen flow rate, reaching 14.5 Ωcm at 50 sccm. Current-voltage (I-V) measurements showed rectifying behavior, with rectification ratios significantly improving at 200°C. The sample with the best rectification performance also exhibited the lowest ideality factor (2.05) and barrier height values ranging from 0.707 to 0.802 eV. These findings highlight the effectiveness of HCP-ALD in producing NiO films with optimized properties, tailored for use in electronic and optoelectronic applications , with the identified optimal growth conditions serving as a benchmark for future studies. • First use of HCP-ALD to deposit promising NiO thin films with nickelocene. • Cost-effective method to tailor optical, structural, and electrical properties of NiO films . • Optimization of deposition parameters leads to noteworthy film quality and electronic behavior. • NiO films exhibit a cubic crystal structure, high refractive index , and low energy dissipation. • Enhanced electrical properties in p-NiO/n-Si junctions for optoelectronic applications .