Effects of substrate traps on turn-on characteristics of GaAs MESFET's are studied by two-dimensional (2-D) simulation. When the off-state gate voltage is much more negative than the threshold (pinch-off) voltage and the surface-state effects are small, abnormal current overshoot and subsequent slow transients are observed for the case with undoped semi-insulating substrate including an electron trap: EL2. Even if the surface-state effects are pronounced to show the large gate-lag, the drain current may show the overshoot-like behavior at relatively early periods. The case of Cr-doped substrate with a hole trap: Cr is also discussed.
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