The Growth Characteristics of a GaN Layer on a Cone-Shaped Patterned Sapphire Substrate by TEM Observation

Abstract

The growth characteristics of a GaN layer deposited on a cone-shaped patterned sapphire substrate (PSS) by using metalorganic chemical vapor deposition (MOVCD) were observed by transmission electron microscope (TEM) to investigate the influence of cone-shaped PSS on the GaN layer. The GaN/sapphire interfaces were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron diffraction (CBED), and the residual strain was evaluated by measuring the variation of the lattice parameters quantitatively. From the TEM images, a large number of threading dislocations were found above the flat region of the GaN/sapphire interface. In contrast, only a few threading dislocations were identified above the cone-shaped region. The HOLZ pattern analysis revealed that the lattice parameter of the GaN layer was lower above the flat region of the GaN/sapphire interface compared with the cone-shaped region, and the difference was estimated to be about 0.1 %. This may be attributed to the formation of a GaN layer by the lateral overgrowth above the cone-shaped region, resulting in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate.