Microstructure and Strain of ZnO Molecular-Beam Epitaxial Layers on Sapphire

Strains and crystalline perfection of ZnO epitaxial layers on sapphire grown by molecular-beam epitaxy were studied using high-resolution X-ray diffractometry. The strain state of samples was determined by curvature measurements. The structural quality of layers was analyzed by diffraction measurements in the Bragg and Laue geometry using theta and (theta-2 theta) scanning modes. It was found that the grown layers (Zn/O > 1) are subject to biaxial tensile stresses, while stresses are absent for Zn/O < 1. The density and depth of different dislocations were calculated from the diffraction peak broadening.