Microstructural analysis of InGaN/GaN epitaxial layers of metal organic chemical vapor deposition on c-plane of convex patterned sapphire substrate

The microstructures of the P-GaN (250 nm)/GaN cap (~35 nm)/7 pairs of InGaN/GaN MQWs (multi-quantum wells)/n-GaN (3 μm)/HT (high temperature)-GaN (3 μm)/LT (low temperature)-GaN buffer (5 nm) on c-plane convex patterned sapphire substrate were analyzed using transmission electronmicroscopy (TEM). High density of dislocations in the LT-GaN buffer layer at both flat and convex patterned regionswas observed to form. At the flat region, some of high dislocations formed at LT-GaN buffer grew over, bended to from stair-like dislocations extended along the edge of the convex pattern and then transformed to TDs (threading dislocations) extending through the InGaN/GaN epitaxial layers. However, few TDs reached the top of the epitaxial layers. Quantitative analysis revealed that the dislocation density has been drastically reduced to ~10⁶ cm^-2, reducing formation of V-defects at the 7 pairs of multi-quantum-wells near the surface.