Growth and characterization of nonpolar a-plane ZnO films on perovskite oxides with thin homointerlayer

Nonpolar a-plane ZnO thin films were deposited on the single-crystal perovskite SrTiO3 (1 0 0) substrates at 750 °C by radio-frequency magnetron sputtering. The effects of ultrathin 30 nm-thick ZnO buffer layer grown at 300–600 °C on the physical properties of ZnO/SrTiO3(STO) thin films are investigated. A high growth temperature of ZnO buffer layer enhances not only the (1 1 0)-texture of ZnO/STO thin films but also the crystalline quality of the film. However, the ZnO/STO thin film without a ZnO buffer layer has a poor crystalline quality comparing to those with the ZnO buffer layer. Atomic force microscopy morphology studies reveal that the ZnO buffer layer largely decreases the surface roughness of the ZnO/STO thin films. This may be because of the thin ZnO buffer layer effectively decreases the stress between the ZnO and STO. The results of X-ray diffraction, high-resolution transmission electron microscopy, and photoluminescence spectra show that a high-quality epitaxial ZnO (1 1 0)/STO (1 0 0) thin film that emits UV light at room temperature can be formed with a thin ZnO buffer layer grown at 600 °C.

Research highlights▶ The 30 nm-thick ZnO buffer layer helps to release the lattice strain of thick ZnO film on the SrTiO3 substrate. ▶ A highly crystalline quality of (1 1 0)-oriented ZnO/SrTiO3 thin film can be grown at a sufficiently high growth temperature of the ZnO buffer layer. ▶ The orthogonal domain structure of the ZnO/SrTiO3 thin films plays an important role to release the lattice misfit strain.