Abstract: A nitride semiconductor material comprising a semiconductor or dielectric substrate having thereon a first nitride semiconductor layer group, wherein the surface of the first nitride semiconductor layer group has an RMS of 5 nm or less, a variation of X-ray half-width within ±30%, a light reflectance of the surface of 15% or more, and a variation thereof of ±10% or less, and the thickness of said first nitride semiconductor layer group is 25 ?m or more. This nitride semiconductor material is excellent in uniformity and stability, assured of a low production cost, and useful as a substrate for a nitride semiconductor-type device.

Abstract: A double hetero type epitaxial wafer contains a single crystal substrate, first and second conductivity type clad layers which are opposite and are made of mixed crystal compounds of Group III-V which had an indirect transition type band structure, and an active layer made of a mixed crystal compound of Group III-V which has a direct transition type band structure and is interposed between the respective clad layers, wherein the first conductivity type clad layer has a refractive index smaller than that of the second conductivity type clad layer.

Abstract: The reproducibility of Te doping in III-V group compounds is improved by using as the dopant a III-V group compound containing Te at a concentration of at least 1.times.10.sup.17 cm.sup.-3.