GaN grown in polar and non-polar directions

In this paper; defects formed in GaN grown by different methods are reviewed. thin GaN films were grown on c-, m- and a-planes on a number of substrates and typical defects as characterized by transmission electron microscopy are described. For polar epilayers grown on c-plane sapphire the typical defects are dislocations (edge, screw and mixed). The lowest dislocation density was obtained for homoepitaxial growth using molecular beam epitaxy (MBE) or hydride vapour phase epitaxy (HVPE). In these cases, the core structure of screw dislocations were studies in detail. In both cases, the cores are full. In the layers grown by HVPE the dislocations are decorated by pinholes stacked on top of each other. These pinholes are empty inside and their formation is attributed to impurities (oxygen) present in these layers. In these layers Ga-rich cores have been found. These were not observed in the layers grown by MBE on the top of the HVPE templates. Epilayers grown in non-polar directions (m- or a-plane) have a high density of planar defects (stacking faults) terminated by partial dislocations. Only low energy faults were found. The majority of these faults are formed at the interface with the substrate and propagate to the sample surface.