Investigation and modeling of impact ionization with regard to the RF and noise behavior of HFET

A new small-signal and noise-equivalent circuit for heterostructure field-effect transistors (HFET's), including the influence of impact-ionization and gate-leakage current on the electronic properties, is presented. The capability of the new model is demonstrated by bias-dependent investigations of the high-frequency (HF) (45 MHz up to 40 GHz) and noise behavior (2 GHz up to 18 GHz) of the InAlAs/InGaAs/InP HFET. Furthermore, based on these results, the bias-dependence of the newly implemented small-signal equivalent elements and the equivalent intrinsic noise sources, are discussed.