Derivation of growth mechanism of nano-defects in GaN from TEM data

Transmission electron microscopy (TEM) has been used to describe 'hollow' defects, e.g. nanotubes and pinholes (empty inside) formed in GaN hetero- and homoepitaxial layers. These defects are believed to be formed due to the presence of impurities and dopants. These defects appear to be even more deleterious than dislocations for the application of GaN in devices because their formation interrupts two-dimensional growth of quantum wells, and therefore will influence electrical and optical properties of the material. Experimental observations show that both these defects start from V-shaped indentations delineated by (1011) planes, and their density increases with higher concentrations of impurities or dopants. These 'hollow' defects are often found to be attached to dislocations, but the frequently observed termination of these defects inside the crystal eliminates dislocations as the source of these defects. Theoretical predictions also do not suggest that dislocations would have large-diameter empty cores like these of nanotubes and pinholes.