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.