Method for manufacturing group III nitride semiconductor substrate

A method for manufacturing a group III nitride semiconductor substrate, the method comprising:

• growing a first AlN buffer layer on a Si substrate at a first growth temperature;
• growing a second AlN buffer layer on the first AlN buffer layer at a second growth temperature higher than the first growth temperature;
• and
• growing a group III nitride semiconductor layer on the second AlN buffer layer, wherein:
• an Al raw material and a N raw material are alternately repeatedly fed in the growing the first AlN buffer layer,
• the first growth temperature is 400° C. to 800° C., and the second growth temperature is 900° C. to 1200° C.,
• a resistivity of the Si substrate is 100 Ωcm or more,
• the Si substrate contains an impurity element selected from C, Ge, Sn, O, H, and a group V element,
• a concentration of the impurity element contained in a surface layer part of the Si substrate ranging from the surface to the depth of 0.5 um to 10 um is 1×1012 atoms/cm3 to 1×1020 atoms/cm3, and
• a concentration of impurity element contained in an area at a depth of greater than 10 μm from the surface is lower than the concentration in the surface layer part.