A Transmission Electron Microscopy Investigation of Gan Grown on Patterned, Step-free 4h-sic Mesas

The development of GaN-based vertical devices with low-leakage currents deposited on SiC represents an important technological challenge for power applications. Threading screw dislocations have been identified as defects that contribute to such leakage [1]. Through the use of patterned SiC substrates that have regions that are free of surface steps, we have previously reported the growth of high-quality GaN heteroepitaxial films with threading dislocation densities on the order of 107/cm2[2]. In addition to the lowdefect densities, we have observed a defect substructure in which lateral a-type dislocations annihilate run parallel to the heterointerface both in the nucleation layer and early in the subsequent GaN growth [2], [3]. Conversely, regions that have surface steps also have accompanying threading dislocations with screw-components in the GaN layer.