Transmission electron microscopy study of a defected zone in GaN on a SiC substrate grown by hydride vapor phase epitaxy

A defected zone (DZ) in the hydride vapor phase epitaxy (HVPE)-deposited GaN located near an interface with a SiC substrate was investigated by transmission electron microscopy for both plan-view and cross-section specimens. Predominant defects in the DZ are dislocations and stacking fault-type interfaces. Analysis of the defects by a moire contrast and high-resolution imaging has suggested that the interfaces resulted from the process of coalescence and overgrowth of three-dimensional nucleated islands. The islands differ by a translation with respect to the reference (substrate) lattice, and therefore their coalescence results in the formation of domains separated by stacking fault-type boundaries. For the HVPE process used in depositing the specimens studied, we infer that the islands adopted the shape of {11(2) over bar l}-faceted truncated pyramids. Continued coalescence and overgrowth of the nonequivalent by translation domains result in a substructure of connected (0001) and {11(2) over bar 0} stacking faults and threading dislocations. The density of these defects decreases with continued coalescence as the growth of GaN progresses, and thus determines the effective thickness of the DZ. We anticipate that the extent of such defected zones depends on the nucleation frequency and anisotropic growth rate of different crystallographic facets. (C) 2003 American Institute of Physics.