The joining of defect-free AlN stripes is observed to trigger the generation of a large density of threading dislocations in the vicinity of the coalescence point. The AlN structure was grown by pulsed lateral epitaxy on shallow-grooved sapphire substrates. In the precoalescence stage, the dislocation density in the lateral epitaxial region (< 108 cm-2) is over two orders of magnitude less than in standard c -plane epitaxy. Basal-plane dislocations (b=a= 1 3 <11 2- 0>) are generated at the coalescence point as a result of relaxation of compressive stress that develops due to temperature gradients during growth. They bend toward the surface during the postcoalescence growth stage, leading to a high density of pure-edge threading dislocations in the lateral growth regions. Some threading dislocations form loops on prismatic planes in the crystal and the basal segments are observed to glide in the  direction under the electron beam in the microscope.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)