No abstract

We investigated both the atomic arrangements in the core structure of threading dislocations (TDs) and their behaviors in unintentionally doped c-plane-GaN layers grown by metalorganic vapor phase epitaxy and hydride vapor phase epitaxy using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The extra image contrast near the core was attributed to an extra displacement in a-type TDs in addition to the core structures revealed in previous reports; we used the notation “with displacement” to describe the new core structure. We found that TDs incline towards both the m- and a-directions from the c-direction. The transition of a-type TDs from the conventional core structure to the structure with displacement was deduced from its relationship to the TD inclination. We also found similarities between a-type screw dislocations and a-type TDs with displacement in the atomic-scale HAADF-STEM images. We concluded that a-type TDs could incline towards the a-direction via a-type screw dislocations, and that these inclined a-type TDs are observed as the core structure with displacement.

We achieve low threading dislocation (TD) density in the order of 104–105 cm−2 over the whole surface of hydride‐vapor‐phase‐epitaxy (HVPE)‐grown GaN, using a facet controlling technique. The SiO2‐striped mask patterns used in this method have 10 μm masking regions and 200 μm‐wide windows for selective area growth. Although this GaN layer was grown using patterned masks, no concentration of dislocations was observed over the whole surface of the GaN layer. We also visualized the unique dislocation behavior over the entire selectively grown GaN layer area. Three‐dimensional distributions of dislocation densities for both the threading and in‐plane dislocations of the HVPE‐grown GaN were obtained by the three dimensional cathodoluminescence imaging using inclined polished specimens.

The effective and uniform reduction of threading dislocation (TD) density using epitaxial lateral overgrowth is an ongoing research challenge. Matsubara et al. (article no. http://doi.wiley.com/10.1002/pssb.201600716) achieved low TD densities on the order of 104–105 cm−2 over the whole surface of hydride vapor phase epitaxy grown GaN using a facet controlling technique and embedded growth. This method involves SiO2 striped mask patterns with 10 μm small masks and 200 μm wide windows for selective area growth. From the three‐directional dark spot density maps, TDs were gathered to the center of the facet growth region by bent TDs and in‐plane dislocations, and likely annihilate or react with each other with a high probability. The residual dislocations in the center of the facet growth region were spread out by bent TDs and in‐plane dislocations to the lateral direction, and no concentration of dislocations at the GaN layer surface was found. The authors visualize this unique dislocation behavior over the entire selectively grown GaN layer area. Three‐dimensional distributions of the dislocation densities of both TDs and in‐plane dislocations were also recorded using cathodoluminescence imaging with inclined‐polished GaN specimens.