Patent ID: 8809868

Claim:
A Group III nitride semiconductor device comprising: a substrate having an electrically conductivity, the substrate including a primary surface, the primary surface comprising a first gallium nitride based semiconductor; a Group III nitride semiconductor region including a first p-type gallium nitride based semiconductor layer and provided on the primary surface, a p-type contact layer, the first p-type gallium nitride based semiconductor layer being provided between the substrate and the p-type contact layer, and the p-type contact layer comprising oxygen as impurity, and an oxygen concentration of the p-type contact layer being more than that of the first p-type gallium nitride based semiconductor layer, and an electrode in direct contact with the p-type contact layer, the primary surface of the substrate being inclined at an angle in a range of not less than 50 degrees and less than 130 degrees from a plane perpendicular to a reference axis, the reference axis extending along a c-axis of the first gallium nitride based semiconductor, an oxygen concentration Noxg of the first p-type gallium nitride based semiconductor layer being not more than 5×10 17 cm −3 , and a ratio (Noxg/Npd) of the oxygen concentration Noxg to a p-type dopant concentration Npd of the first p-type gallium nitride based semiconductor layer being not more than 1/10.