Dislocation propagation in GaN films formed by epitaxial lateral overgrowth

We have investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) the relationship between surface morphological evolution and dislocation propagation in GaN films formed by epitaxial lateral overgrowth (ELO) in hydride vapour phase epitaxy. The SEM observations revealed that step and terrace structures were formed on (0001) surfaces of the films both in the earlier and the later stages of growth, suggesting the occurrence of step-flow growth during ELO. Bending dislocations with laterally propagated segments were frequently observed in the ELO films and their morphology led to a reduction in threading dislocation density in the film surface regions. Systematic TEM observations were performed to reveal the detailed structure of the bending dislocations. Comparison between the SEM and the TEM results showed that the lateral propagation of the dislocation was closely related to the appearance of the [1101) facets. A mechanism for dislocation propagation is discussed that explains the observed dislocation structure and surface step morphology.