An investigation was made of the characteristics of dislocations in ZnO layers grown onto sapphire by plasma-assisted molecular beam epitaxy under various Zn/O flux ratios. The ZnO layers were characterized by means of transmission electron microscopy and high-resolution X-ray diffraction. The transmission electron microscopic and high-resolution X-ray diffraction experiments revealed that the main threading dislocations in the ZnO layers were edge dislocations running along the c-axis, with a Burgers vector of 1/3<11▪0>. The threading dislocation densities were found to be 6.9 x 109, 2.8 x 109 and 2.7 x 109/cm2 for O-rich, stoichiometric and Zn-rich ZnO, respectively. Contrary to O-rich ZnO where the dislocations ran along the c-axis, several dislocations in stoichiometric and Zn-rich ZnO were inclined by 20° to 30° from the c-axis. By considering the slip system in the wurtzite-structured ZnO, the glide planes of the dislocations were found to be close to (10▪0) for O-rich ZnO and close to (10▪1) for stoichiometric and Zn-rich ZnO. The thickness of the interface dislocations in O-rich ZnO was much less than in stoichiometric and Zn-rich ZnO.

Characteristics of Dislocations in ZnO Layers Grown by Plasma-Assisted Molecular Beam Epitaxy under Different Zn/O Flux Ratios. A.Setiawan, Z.Vashaei, M.W.Cho, T.Yao, H.Kato, M.Sano, K.Miyamoto, I.Yonenaga, H.J.Ko: Journal of Applied Physics, 2004, 96[7], 3763-8