Recent progress in group-III nitride light-emitting diodes

We review the recent progress of nitride-based light-emitting diodes (LEDs) and discuss the dislocation issue and luminous efficiency. First, candela-class blue LEDs have been developed. InGaN layer was used for nitride LEDs instead of GaN active layer. The quantum-well-structure InGaN active layer dramatically improved the external quantum efficiency. There are a number of threading dislocations in epitaxial layer of nitride-based LEDs. InGaN-LEDs, however, have quite high external quantum efficiency. With regard to this, it is thought that the fluctuation of indium mole fraction is strongly related to the high external quantum efficiency. We also discuss the method to improve the external quantum efficiency of nitride-based LEDs.