Nitride semiconductor device, nitride semiconductor wafer and method for manufacturing nitride semiconductor layer

A nitride semiconductor wafer, comprising:

• a silicon substrate;
• an Al-containing nitride semiconductor layer provided on the silicon substrate;
• a foundation layer provided on the Al-containing nitride semiconductor layer, the foundation layer having a thickness not less than 1 micrometer, and including GaN;
• and
• a functional layer provided on the foundation layer and directly contacting the foundation layer, the functional layer including a first semiconductor layer, the first semiconductor layer including GaN containing an impurity of Si, the first semiconductor layer having an impurity concentration higher than an impurity concentration in the foundation layer,
• the Al-containing nitride semiconductor layer including a multilayer structure body,
• the multilayer structure body including a first layer including an Al-containing nitride semiconductor and a second layer including an Al-containing nitride semiconductor, the second layer being stacked with the first layer,
• an Al containing ratio of the second layer being smaller than an Al containing ratio of the first layer, and
• the thickness of the foundation layer being thinner than a thickness of the first semiconductor layer.

A method for manufacturing a nitride semiconductor layer, comprising:

• forming an Al-containing nitride semiconductor layer on a silicon substrate;
• forming, on the Al-containing nitride semiconductor layer, a foundation layer having a thickness not less than 1 micrometer and including GaN;
• and
• forming, on the foundation layer and directly contacting the foundation layer, a functional layer including a first semiconductor layer, the first semiconductor layer including GaN containing an impurity of Si, the first semiconductor layer having an impurity concentration higher than an impurity concentration in the foundation layer,
• the Al-containing nitride semiconductor layer including a multilayer structure body,
• the multilayer structure body including a first layer including an Al-containing nitride semiconductor and a second layer including an Al-containing nitride semiconductor, the second layer being stacked with the first layer,
• an Al containing ratio of the second layer being smaller than an Al containing ratio of the first layer, and
• the thickness of the foundation layer being thinner than a thickness of the first semiconductor layer.