We analyze the internal quantum efficiency (IQE) of whole-composition-range AlGaN multiquantum wells (MQWs) on AlGaN with various dislocation densities (DDs) by excitation-density-dependent photoluminescence measurement. IQEs of deep ultraviolet/ultraviolet (DUV/UV) MQWs are strongly dependent on the DD. IQE with an excess carrier density of 1×1018 cm-3 changes from 4 to 64% when the DD changes from 6×109 to 2×108 cm-2. This trend is almost the same for DUV/UV MQWs with emission wavelength ranging from 230 to 350 nm. Thus, the reduction of the DD is very important for the realization of a high-IQE DUV/UV active layer.

Using the epitaxial lateral growth technique, we compared the crystallinity and relaxation ratio of 3-µm- and 200-nm-thick Al0.5Ga0.5N on an AlN template and AlN grown by epitaxial lateral overgrowth (ELO-AlN), both of which were grown on a sapphire substrate. Although the relaxation ratios of 3-µm-thick Al0.5Ga0.5N were almost the same, the misfit dislocation density at the interface and the density of threading dislocations reaching the surface of Al0.5Ga0.5N were significantly different. Also, the increase in the density of newly generated misfit dislocations was found to be highly dependent on the quality of the AlN underlying layer. We also discuss the difference in the initial growth mode of each Al0.5Ga0.5N sample.