III nitride semiconductor epitaxial substrate and III nitride semiconductor light emitting device, and methods of producing the same

A method of producing a III nitride semiconductor epitaxial substrate, comprising the steps of:

• forming an undoped AlN layer on a substrate of which at least a surface portion is made of AlN;
• forming an Si-doped AlN buffer layer on the undoped AlN layer;
• and
• forming a superlattice laminate on the Si-doped AlN buffer layer,
• wherein in the step of forming the Si-doped AlN buffer layer, Si doping is performed such that an Si concentration of 2.0×1019/cm3 or more is achieved and a thickness of the Si-doped AlN buffer layer is in a range of 4 nm to 10 nm,
• the superlattice laminate is formed by (i) stacking high Al-content layers represented by AlxGa1-xN, where x is an average composition in a crystal growth direction and x satisfies 0.9<x≦1, on the Si-doped AlN buffer layer and (ii) alternately stacking n sets, where n is an integer satisfying 4≦n≦10, of low Al-content layers and the high Al-content layers, each of the low Al-content layers being represented by AlyGa1-yN, where y is an average composition in the crystal growth direction and y satisfies 0<y<x, and
• the first to (n−2)th low Al-content layers from the Si-doped AlN buffer layer side have a first thickness, the (n−1)th low Al-content layer has a second thickness larger than the first thickness, and the nth low Al-content layer has a third thickness equal to or larger than the second thickness.