Properties of (11–20) a-plane ZnO films on sapphire substrates grown at different temperatures by plasma-assisted molecular beam epitaxy

The effects of growth temperatures (in a wide range from 100 to 800 °C) on properties of a-plane (11 2 ¯ 0) ZnO films grown on r-plane (1 1 ¯ 02) sapphire substrates by plasma-assisted molecular beam epitaxy were investigated. The film was grown as polycrystalline at 100 °C, but grown as single crystalline at the temperatures from 200 to 800 °C without any mixture of c-plane (0001) ZnO and m-plane (10 1 ¯ 0) ZnO. The single crystalline ZnO films showed anisotropic surface morphology with the conglomerated granules or striations along the [0001] ZnO direction. The ZnO film grown at 400 °C showed better crystal quality than others. It showed the smallest full width at half maximums of 0.450° and 0.297° for (11 2 ¯ 0) x-ray omega rocking curves under the measuring configuration with the omega axis parallel and perpendicular to the ZnO and directions, respectively, and 0.387° for (10 1 ¯ 1) omega rocking curve. The threading dislocation and the stacking fault densities were determined to be ~ 3.7 × 10 10 cm −2 and ~ 8.5 × 10 4 cm −1 for the ZnO film grown at 400 °C.