1. Field of the Invention
The present Invention relates to a sapphire substrate for a nitride semiconductor light emitting element and a method for manufacturing the same and a nitride semiconductor light emitting element.
2. Description of Related Art
Generally, a light emitting diode (LED) made of a nitride semiconductor is constituted by laminating on a sapphire substrate an n-type semiconductor layer, an active layer and a p-type semiconductor layer in this order. Light generated in this light emitting diode at the active layer is extracted from a side opposite to the sapphire substrate or from the sapphire substrate side, while the generated light is also radiated to a direction opposite to a light exiting side. Therefore, it is necessary to improve external quantum efficiency by allowing light radiated to a direction opposite to the light exiting side to be extracted effectively from the light exiting side.
Therefore, JP 2008-177528A, for example, discloses that an external quantum efficiency of a semiconductor light emitting element is improved by arranging a plurality of projections having truncated triangular pyramidal-shape on a sapphire substrate. It also describes that the generation of voids and the deterioration of crystallinity can be suppressed by growing a nitride semiconductor crystalline on a surface on which truncated triangular pyramidal-shaped projections are formed.
However, with an increase in an output of light emitting diodes, it has been found as a result of the present inventors' studies that problems due to crystal defects become apparent, which were not recognized in the previous light emitting diodes. In addition, further improvements are desired in a light extraction efficiency of light emitting diodes.
Thus, an object of the present invention is to provide a sapphire substrate and a method for manufacturing the same, which enables growth of a nitride semiconductor having excellent crystallinity and can provide a nitride semiconductor light emitting element having excellent light extraction efficiency.
Furthermore, an object of the present invention is to provide a nitride light emitting element which comprises a nitride semiconductor having excellent crystallinity and light extraction efficiency.