EPITAXIAL SUBSTRATE, SEMICONDUCTOR DEVICE, METHOD FOR MANUFACTURING EPITAXIAL SUBSTRATE, METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE, AND METHOD FOR ALIGNING DISLOCATION IN GROUP III NITRIDE CRYSTAL

摘要

The present invention provides an epitaxial substrate which is appropriate for the generation of a group III nitride crystal having excellent crystal quality. An upper layer 2 of a group III nitride is formed on a sapphire base with an off angle, and after that a heating process is performed at a temperature not lower than 1500°C, preferably not lower than 1650°C, and thereby, the crystal quality of the upper layer 2 is improved and repeating steps of which the size is greater than the height of several atomic layers are provided on the surface of the upper layer 2, and thus obtained epitaxial substrate 10 is used as a base substrate for growing a group III nitride crystal layer 3. The group III nitride crystal grows from the points of steps in a manner of step flow, and therefore, threading dislocations from the upper layer 2 are bent according to this growth, and are unevenly distributed as the crystal grows afterwards. The obtained group III nitride crystal layer 3 has an excellent surface flatness, and most portions in the vicinity of the surface become low dislocation regions where the density of dislocations is approximately 1 × 10 7 /cm 2 . That is, it can be said that the epitaxial substrate 10 is appropriate for the formation of a group III nitride crystal having excellent crystal quality.