For example, a light emitting diode (LED) made of a nitride semiconductor is usually constituted by sequentially laminating an n-type semiconductor layer, an active layer and a p-type semiconductor layer on a sapphire substrate. In this light emitting diode, emitted light is extracted from the side opposite the sapphire substrate or the side of the sapphire substrate, while light emitted from the active layer is also radiated in a direction opposite the light emission side. Therefore, it becomes necessary to improve external quantum efficiency by enabling light radiated in a direction opposite the light emission side to extract effectively from the light emission side.
For example, Patent Document 1 discloses that external quantum efficiency is improved by arranging a plurality of projections having truncated triangular pyramid-shaped on a sapphire substrate. Patent Document 1 also describes that generation of voids and deterioration of crystallinity can be suppressed by enabling crystal growth on a surface, on which projections having a truncated triangular pyramid shaped are formed, through the projections.
USPTO Backgrounds
USPTO Backgrounds