| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration of the high-frequency characteristic of a field effect transistor resulting from the auto-doping of a buffer layer with silicon by providing an oxidized AlXGa1-XAs (where, X falls within a specific range) layer between the buffer layer and an active layer. SOLUTION: An AlXGa1-XAs (0.9<=X<=1) layer '8 has a thickness of >=500Å, exhibits a specific resistance of >=1×105Ωcm when wet-oxidized, and can remarkably increase the insulation between an active layer 6 and a gate electrode 1 and a silicon substrate 4. In addition, since the AlXGa1-XAs layer '8 is wet-oxidized through a hole 9 formed in the rear surface of the substrate 4 by etching, the step of a mesa M can be reduced remarkably.
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