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

Abstract

The effects of growth temperatures (in a wide range from 100 to 800 degrees C) on properties of a-plane (11 (2) over bar0) ZnO films grown on r-plane (1 (1) over bar 02) sapphire substrates by plasma-assisted molecular beam epitaxy were investigated. The film was grown as polycrystalline at 100 degrees C, but grown as single crystalline at the temperatures from 200 to 800 degrees C without any mixture of c-plane (0001) ZnO and m-plane (10 (1) over bar0) 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 degrees C showed better crystal quality than others. It showed the smallest full width at half maximums of 0.450 degrees and 0.297 degrees for (11 (2) over bar0) x-ray omega rocking curves under the measuring configuration with the omega axis parallel and perpendicular to the < 0001 >(ZnO) and directions, respectively, and 0.387 degrees for (10 (1) over bar1) omega rocking curve. The threading dislocation and the stacking fault densities were determined to be similar to 3.7 x 10(10) cm(-2) and similar to 8.5 x 10(4) cm(-1) for the ZnO film grown at 400 degrees C.