Defect structure of epitaxial ZnO films on (0001) sapphire studied by transmission electron microscopy

Defects and structural characteristics (threading dislocations and angles o f rotational disorder in the subgrain) of wurtzite-type ZnO films grown by electron cyclotron resonance-assisted molecular beam epitaxy on (0001) c-pl ane sapphire have been investigated extensively using conventional transmis sion electron microscopy and high-resolution electron microscopy (HREM). Th rough the cross-sectional and plan-view observations, the existence of thre ading dislocations in the ZnO film and the basic crystallographic orientati on relationship of (0001)(ZnO)\ \ (0001)(sapphire) and [2 (1) over bar(1) o ver bar0](ZnO)\ \ (1 (1) over bar 00)(sapphire) were clarified. The line di rections of most threading dislocations were found to be normal to the inte rface. The density of the threading dislocations in ZnO film was estimated to be 1.9x 10(11) cm(-2) and the subgrains being accompanied by the threadi ng dislocations and Burgers vectors of 1/3(11 (2) over bar0) were clearly o bserved. It was found that the size of the subgrains ranges from 15 to 150 nm and the subgrains are rotated by 1 degrees -5 degrees with respect to th e ZnO film. The overlapping manner of the ZnO film and the sapphire substra te in the subgrains was discussed taking into account the moire fringes of HREM images. (C) 2001 American Vacuum Society.