Impact-ionization effects on the high-frequency behavior of HFETs

A new small-signal equivalent-circuit model is presented, which takes into account strong impact-ionization effects on the high-frequency behavior of heterostructure field-effect transistors (HFET). The proposed model overcomes the limitations of previous models and includes the bipolar action of the space charge of holes generated by impact ionization. It is shown that the developed model is capable of explaining the anomalous high-frequency behavior of HFETs with channels of high indium content.