We demonstrate that the performance of silicon carbide MESFETs is largely determined by short-channel effects. Parasitic bipolar transistor turn-on limits the operation voltage to a small fraction of the theoretically expected value for an ideal device. Tradeoffs are shown to exist between optimum gate length and on-state current on one hand, and the maximum blocking voltage on the other hand. Composite p-buffers with an elevated doping in the vicinity of the active layer considerably increase the operation voltage. Silicon carbide MESFETs utilizing composite buffers are reported.
Low-loped p-type silicon carbide buffer layers are grown by chemical vapor deposition on conducting and semi-insulating substrates. Capacitance-voltage and electrical admittance techniques are developed for accurate non-destructive characterization. The electrical admittance techniques suggested are capable of measuring the resistivity in a very wide range, up to 7 orders of magnitude. MESFET devices using thick buffer layers on conducting substrates are reported with Ft=8.4 GHz and Fmax=32 GHz.
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