Crystal substrate, ultraviolet light-emitting device, and manufacturing methods therefor

A method for manufacturing a crystal substrate of a non-polar orientation comprising the steps of:

• providing a sapphire crystal plate of an r-plane orientation;
• and
• forming a buffer layer of an AlN buffer layer, so that the AlN buffer layer covers at least a part of a surface of the sapphire crystal plate, the AlN buffer layer being an epitaxially grown layer of AlN crystal of a non-polar orientation,
• wherein the step of forming a buffer layer comprises the steps of:
• forming a surface protection layer by epitaxially growing a surface protection layer that suppresses roughness on a surface of the AlN buffer layer;
• and
• smoothing by epitaxially growing a smoothing layer on the surface protection layer for providing a surface of the AlN buffer with a smoothed upper surface.

A method for manufacturing an ultraviolet light emitting device on a crystal substrate comprising steps of:

• providing a crystal substrate having a non-polar AlN surface;
• and
• forming a group-III nitride semiconductor crystal layer by epitaxially growing an ultraviolet (UV) emission layer of a non-polar plane on at least a part of the non-polar AlN surface of the crystal substrate, the UV emission layer comprising an n-type conduction layer, a recombination layer, and a p-type conduction layer in this order from the crystal substrate side, all of which are made of group-III nitride semiconductor crystal;
• and
• forming a reflective electrode by disposing a reflective electrode directly or indirectly via another layer on the p-type conductive layer, the reflective electrode having a reflection capability for UV radiation that is an ultraviolet light from the UV emission layer.