| 摘要 |
PROBLEM TO BE SOLVED: To provide a semiconductor field effect transistor wherein high power output, high frequency and high efficiency can be obtained at a gate length of at most 1μm, and a power amplifier using the field effect transistor. SOLUTION: A buffer layer 13 composed of AlxGa1-xN (0<x<1) is arranged below a GaN electron transit layer 14, and negative piezoelectric charges are accumulated in this interface. A cap layer 15 composed of AlyGa1-yN (0<x<y<1) is arranged above the GaN electron transit layer 14, and positive piezoelectric charges are accumulated in this interface. As a result, a current can be confined in the GaN electron transit layer 14, and off-characteristic of a field effect transistor is improved.
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