Published online by Cambridge University Press: 17 March 2011
Cross sectional transmission electron microscope (TEM) observation has been performed for specimens of ELO-GaN (ELO: epitaxial-lateral-overgrowth) in order to analyze the behavior of dislocations, with special reference to the effect of facet plane orientation and the size of mask. An ELO-GaN layer was grown overlying on a thick GaN layer with a patterned mask by MOVPE with a carrier gas of hydrogen (H2) under a low-ambient pressure. The growth temperature and the reactor-pressure were controlled in a two-step way during the growth of ELO-GaN layer in order to change the dominant facet-planes and the aspect ratio in growth rate. The experimental results revealed that (a+c)-type threading dislocations (TDs) show a 90-degree-bending in the specimen with slanting facets (2 1 1 2), but not in those with vertical ones (2110). a-type TDs run upward without bending irrespective of the orientation of the facet planes. Dislocations lying on (0001) planes, or horizontal dislocations (HDs), have been generated in the specimens with wide mask-terraces. It is thought that the formation of HDs relieved stresses in the ELO-GaN and then suppressed the bending of a-type TDs. In the specimens with narrow terraces, the both type TDs penetrate upward without bending and few HDs are generated. The behavior of dislocations is attributable to the fact that the small size of terrace generates small stresses and promotes a fast meeting of wings of ELO-GaN.