Differences and similarities between structural properties of GaN grown by different growth methods

In this paper, defects formed in GaN grown by different methods are reviewed. The crystal growth direction and growth rate play important roles. For bulk crystals grown under high pressure the highest growth rates are for planes perpendicular to the c-axis. Only planar defects formed on c-planes are observed in these crystals. There are no threading dislocations or nanotubes in the c-direction. However, polarity of the growth direction plays a role in the surface roughness and the distribution of planar defects. For the growth of homo-epitaxial and hetero-epitaxial layers, the growth is forced to take place in the much slower c-direction. As a result, defects related to the purity of constituents used for the growth are formed such as nanotubes and pinholes. In addition, threading dislocations and dislocations that accommodate lattice and thermal expansion mismatch are formed.