Electrical properties of ZnO thin films grown on a-plane sapphire substrates using catalytically generated high-energy H2O

•ZnO films were grown by CVD using reaction of high-energy H2O and dimethylzinc gas.•Films were grown on a-plane sapphire substrates at 773 K.•ZnO film at 2.8 µm thick exhibited a large electron mobility of 189 cm2/Vs at room temperature.•From the crystallinity and the electrical properties for various film thicknesses, the structure of the ZnO films was estimated.•The electron mobility and electron concentration of the upper layer were corrected according to a two-layer Hall-effect model.

The electrical properties of zinc oxide (ZnO) epitaxial films grown by chemical vapor deposition (CVD) using high-energy H2O generated by H2–O2 reactions on Pt nanoparticles were evaluated. High-energy ZnO precursors formed by the reaction between dimethylzinc gas molecules and H2O molecules were supplied to the substrate surface. The ZnO epitaxial films were grown directly on a-plane sapphire (a-Al2O3) substrates at 773 K without any buffer layer. The electron mobility (μH) at room temperature increased from 30 to 190 cm2V− 1 s− 1 with increasing film thickness from 100 nm to 2800 nm. The μH increased significantly with decreasing temperature to approximately 100–150 K, but it decreased at temperatures less than 100 K for films thicker than 500 nm. The μH of the ZnO film (189 cm2V− 1 s− 1) at 290 K increased to 660 cm2V− 1 s− 1 at 100 K. In contrast, μH hardly changed with temperature for films thinner than 500 nm. According to a two-layer Hall-effect model, the μH and electron concentration of the upper layer were corrected based on the above results, assuming that the degenerate layer had a thickness of 100 nm.