The small-signal equivalent circuit of AlGaN/GaN HEMT is discussed It is shown that an extremely high gate voltage has to be applied to correctly determine series resistances. Effects appearing at high forward gate voltages are discussed. Good agreement between measured and simulated data has been achieved.

For improved non-linear modeling of AlGaN/GaN high electron mobility transistors, a largesignal model originally developed for GaAs-based devices has been extended by introduction of a thermal sub-circuit to account for self-heating. Thereby, DC output characteristics which typically show negative output conductance at a high dissipating power level are well reproduced. Since self-heating also effects the transconductance, which is related to S 2 1 at RF conditions, the comparison of broadband S-parameter simulations and measurements revealed significant improvement when using the extended model. First experimental and theoretical investigations on the transient behavior at pulsed conditions are finally presented.

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