Threshold voltage controls of Ni/Ti/Au gate and Ti/Au gate 2DEG AlGaAs/GaAs FET's through only heat treatment are investigated. Ni/Ti/Au gate FET's vary over quite a wide range from a depletion mode to an enhancement mode without degradation of FET characteristics after heat treatment at 300°C. The same experiment is made for Ti/Au gate FET's, but the threshold voltage change is negligibly small. It is confirmed that Ni/Ti/Au can be used as the gate metal for E-FET and Ti/Au as the gate metal for D-FET under simultaneous heat treatment. In addition, a mechanism for penetrating the barrier metal into the underlying layer is discussed.
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