Theoretical aspects and microstructural investigations on V-pit defects in HVPE grown GaN

In this work typical V-pits in gallium nitride (GaN) grown by hydride vapour phase epitaxy (HVPE) were investigated by different electron microscopy techniques. Based on this experimental analysis the origin of V-pits is theoretically motivated and discussed. The considerations are compared to the findings on open core dislocations in the case of SiC. The V-pits observed can be divided into two general cases which we call the ""intrinsic"" induced and ""extrinsic"" provoked V-pits. The origin for intrinsic V-pits appear to be super screw dislocations, which tend to form an inner surface, due to energetic reason that will be explained in detail. Contrary to SiC it is energetically more favourable for GaN to create pyramidal facets. Therefore GaN rather forms V-pits instead of micro pipes like they appear in SiC. The reasons for so called ""extrinsic V-pits"" can be various as discussed in the paper. Complementary microstructural investigations carried out with different electron microscopy techniques show, that the theoretical considerations can be proven by microstructural features observed in different GaN samples. The general conclusions from the findings with regard to crystal growth of bulk crystals like the strong tendency for faceting, stability of the growing crystal interface or the diameter reduction is discussed.