Reduction of threading dislocations in epitaxial ZnO films grown on sapphire (0001)

Transmission electron microscopy was used to investigate epitaxial ZnO films on c-sapphire, produced by a two-step method. Firstly, pulsed laser deposition provided a continuous buffer ZnO, with thickness about 80 nm and a predominant alignment of (0001)(ZnO)//(0001)(sapphire) and [11-20](ZnO)//[10-10](sapphire). On the top of buffer layer there was a high density of c-aligned nanorods, which revealed few, if any, threading dislocations (TDs), in contrast with the buffer layer where TD density was about 10(11)/cm(2). Subsequent treatments by either chemical vapour deposition or hydrothermal growth caused the nanorods to grow laterally and form continuous films. Subgrain boundary dislocations were generated as nanorods coalesced, but these new TDs were also annihilated in dislocation reactions, giving to a substantial reduction ill the total TD density.