Ryo Inomoto

InGaN-Based Light-Emitting Diodes Fabricated on Nano Patterned Sapphire Substrates with Pillar Height of More than 600 nm by Nanoimprint Lithography

GaN-based light-emitting diodes (LEDs) were fabricated on nano patterned sapphire substrates (nano-PSSs) by nanoimprint (NIP) lithography. A nano-PSS with a pillar height of more than 600 nm was achieved. The surface emission of the LEDs was strongly affected by pillar height, and the surface emission intensity was highest at a pillar height of 250 nm. In contrast, the external quantum efficiency of the LEDs on the nano-PSSs with diameters of 100 and 450 nm was approximately 30% higher than that on a flat sapphire substrate, which is similar to that on a conventional PSS.

Direct observation of inclined a -type threading dislocation with a -type screw dislocation in GaN

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 sc...