| 摘要 |
PURPOSE:To improve FET characteristics such as mutual conductance by employing an undoped semi-insulating substrate which does not contain impurity for insulation as a semi-insulating substrate. CONSTITUTION:An undoped semi-insulating substrate which is not doped with impurity for insulation such as Cr is employed as a semi-insulatin GaAs substrate 5. This semi-insulating GaAs substrate 5 is formed by a liquid enclosed Czochralski (LEC) method and shows high quality such as low etching pit density. Moreover, a buffer layer 6, an active layer 7 and an ohmic contact layer 7 which are formed on the main surface of the semi-insulating GaAs substrate 5 successively are formed by an organic metal epitaxial growth (MOOCVD) method respectively with uniform quality. Therefore, the thickness of the buffer layer 6 is so selected as to be thicker than the thickness at which the electron mobility in the aotive layer 7 starts declining suddenly and thinner than the thickness at which the leakage current in the buffer layer 6 appears or starts increasing suddenly.
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