| 摘要 |
PURPOSE:To obtain an FET with every little leakage current by a method wherein an intermediate layer, whose composition structure is such that the composition is equal to the composition of an active layer on the side of the active layer and gradually inclined toward the side of a substrate, is provided between the active layer and the semi-insulating substrate. CONSTITUTION:A conventional step hetero junction can not block a leakage current sufficiently. When an FET whose active layer is composed of N-type channel GaAs is formed, an inclined hetero junction is employed. An AlxGa1-xAs intermediate layer 25 is provided between a GaAs active layer 24 and a semi-insulating GaAs substrate 26 and the composition ratio (x) is zero at the boundary of the layers 17 and gradually increased. The conduction band energy difference DELTAE (eV) in the intermediate layer 25 is approximately 0.8x (eV). If the thickness of the intermediate layer 25 is denoted by (d), an electric field Ebi=DELTAEc/d (v/cm) is induced in the layer. As (d) denotes the thickness of a thin film, the high voltage Ebi is induced so that electrons which flow toward the substrate and have possibility of making a leakage current are pushed back into the active layer so that the leakage current is blocked. When In1-xGaxAsyP1-y is employed, the leakage current can be also blocked effectively as described above.
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