Patent ID: 8421190

Claim:
A group III nitride semiconductor substrate containing at least one element selected from the group consisting of O, Si, S, Ge, Se, and Te as an impurity element in concentration of at least 1×10 17 cm −3 wherein: in-plane distribution of the concentration of said impurity element represented as a ratio of a maximum concentration to a minimum concentration of said impurity element in a main surface of the substrate is in a range from at least 1 to at most 3, said group III nitride semiconductor substrate has resistivity of at most 1Ω·cm and thickness of at least 70 μm, and said group III nitride semiconductor substrate is epitaxially grown on another group III nitride semiconductor substrate containing at least one element selected from the group consisting of C, Mg, Fe, Be, Zn, V, and Sb as another impurity element in concentration of at least 1×10 17 cm −3 , wherein: in-plane distribution of the concentration of said another impurity element represented as a ratio of a maximum concentration to a minimum concentration of said another impurity element in a main surface of the substrate is in a range from at least 1 to at most 3, and said another group III nitride semiconductor substrate has resistivity of at least 1×10 4 Ω·cm and thickness of at least 70 μm.