Defect characterization in ZnO layers grown by plasma-enhanced molecular-beam epitaxy on (0001) sapphire substrates

The structural properties of high-quality $(0001)ZnO/Al2O3$ films grown by plasma-enhanced molecular-beam epitaxy are investigated by x-ray diffraction and transmission electron microscopy. The only defects encountered are threading dislocations with a density of $1010–4×1010 cm−2.$ Most numerous dislocations are pure-edge dislocations (Burgers vector of $1/3〈112̄0〉),$ which accommodate slight in-plane misorientations between subgrains. The oxygen polarity of these films is also established.