Patent ID: 7919831

Claim:
A nitride semiconductor device comprising: an n-type gallium nitride single crystal substrate having a hydrogen concentration of less than or equal to 2×10 17 cm −3 and having a C-plane surface; epitaxially grown nitride films on the n-type gallium nitride single crystal substrate; and electrodes deposited on a top of the epitaxially grown nitride films and on a bottom of the gallium nitride single crystal substrate, wherein the n-type gallium nitride single crystal substrate is produced by the steps of: preparing a C-plane gallium nitride single crystal seed having a C-plane surface or a foreign material single crystal seed having three-rotational symmetry; supplying the C-plane gallium nitride single crystal seed or the foreign material single crystal seed with material gases including a gallium material, a nitrogen material and an oxygen containing material; growing a gallium nitride bulk crystal that has micro C-planes and micro hexagonal or dodecagonal cone pits consisting of micro facets having non-C-planes upon the C-plane gallium nitride single crystal seed or the foreign material single crystal seed in vapor phase; maintaining the micro C-planes and the micro facets having the non-C-planes on the growing gallium nitride bulk crystal; doping the growing gallium nitride bulk crystal with oxygen via the micro facets with an efficiency more than 50 times as large as via the micro C-planes; eliminating the foreign material single crystal seed or the C-plane gallium nitride single crystal seed from the grown gallium nitride bulk crystal; polishing the faceted surface of the grown gallium nitride bulk crystal; and obtaining a flat C-plane surface gallium nitride substrate having an n-type carrier density of more than or equal to 5×10 18 cm −3 at points which were covered with the micro facets and having an n-type carrier density of less than or equal to 1×10 17 cm −3 at points which were covered with the C-planes.