Compound semiconductor substrate and compound semiconductor device comprising a Si substrate a SiC layer, nitride semiconductor layers, an electronic traveling layer, and a barrier layer

A compound semiconductor substrate comprising:

• a Si substrate with O concentration of 3*107/cm3 or more and 3*1018/cm3 or less,
• a SiC layer formed on the Si substrate,
• a first nitride semiconductor layer made of AlxGa1-xN (0.1≤x≤1), formed on the SiC layer and including an insulating or semi-insulating layer,
• a second nitride semiconductor layer formed on the first nitride semiconductor layer and including a main layer comprising of insulating or semi-insulating AlyGa1-yN (0≤y<0.1),
• an electronic traveling layer formed on the second nitride semiconductor layer and made of AlzGa1-zN (0≤z<0.1), and
• a barrier layer formed on the electronic traveling layer and having a wider band gap than a band gap of the electronic traveling layer, wherein
• a sum total thickness of the first and second nitride semiconductor layers and the electronic traveling layer is 6 micrometers or more and 10 micrometers or less,
• the first nitride semiconductor layer includes a low concentration region made of AlxGa1-xN (0.1≤x≤0.4) having a thickness of 0.5 micrometer or more,
• the low concentration region has a Si concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less, an O concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less, and a Mg concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less,
• the first nitride semiconductor layer consists of a layer intentionally doped with C, a C concentration in the low concentration region is higher than any of the Si concentration, the O concentration, and the Mg concentration in the low concentration region, and is 5*1019 atoms/cm3 or less,
• a Si concentration, an O concentration, a Mg concentration, a C concentration and an Fe concentration of the electronic traveling layer are all greater than 0 and less than or equal to 1*1017 atoms/cm3,
• the first nitride semiconductor layer further includes a high concentration region made of AlxGa1-xN (0.4<x≤1),
• the high concentration region has a Si concentration of 0 atoms/cm3 or more and 5*1017 atoms/cm3 or less, an O concentration of 0 atoms/cm3 or more and 5*1017 atoms/cm3 or less, and a Mg concentration of 0 atoms/cm3 or more and 5*1017 atoms/cm3 or less,
• the main layer has a Si concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less, an O concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less, and a Mg concentration of 0 atoms/cm3 or more and 2*1016 atoms/cm3 or less,
• a C concentration and/or an Fe concentration in the second nitride semiconductor layer are/is higher than any of the Si concentration, the O concentration, and the Mg concentration in the second nitride semiconductor layer and are/is 5*1019 atoms/cm3 or less, and
• the main layer includes a region where a concentration of activated donor ions is 0 atoms/cm3 or more and 2*1014 atoms/cm3 or less.