The reduction of threading dislocations in GaN using a GaN nanocolumn interlayer

Epitaxial lateral overgrowth (ELO) has been used to reduce threading dislocation (TD) densities in GaN. This paper reports transmission and scanning electron microscopy studies of TDs in GaN films grown by ELO on GaN nanocolumns produced either during growth by MBE (method 1), or by self-organised patterning on a uniform layer grown by MOCVD (method 2). In method 1, isolated nanocolumns grew without TDs, but some TDs formed when nanocolumns coalesced. Although some of these TDs extended through the overlayer, extensive lateral migration of others, depending on the dislocation type, led to dislocation annihilation, lowering the overall TD density. In method 2, a similar process of lateral migration of TDs was observed during ELO, resulting in a continuous GaN overlayer with TD densities less than 10⁸ cm^-2.