Atomic Layer Deposition of Transparent p-Type Semiconducting Nickel Oxide Using Ni(DAD)₂ and Ozone

A novel atomic layer deposition (ALD) process for nickel oxide (NiO) is developed using a recently reported diazadienyl complex, Ni(DAD)₂, and ozone. A window of constant growth per cycle is found between 185 and 200 °C at 0.12 nm/cycle, among the highest reported for ALD NiO. For films deposited at 200 °C, grazing-incidence X-ray diffraction indicates a randomly oriented polycrystalline cubic NiO phase. X-ray photoelectron spectroscopy shows good agreement with bulk NiO reference spectra and no detectable impurities. Atomic force microscopy reveals low root mean square roughness of 0.6 nm for an 18 nm thick film. The refractive index of 2.36 and an electronic bandgap of 3.78 eV, as determined by variable angle spectroscopic ellipsometry, are close to reported values for bulk and thin film NiO. Finally, fabricated Ag/NiO/n-Si/In heterojunction diodes show a current-voltage asymmetry of 1.27 × 10⁴ at 2.3 V and an ideality factor of 3.5, confirming the intrinsic p-type semiconducting behavior of transparent NiO.