At bias extraction of parasitic source and drain resistances in AlGaN/GaN HFETs: bias dependence and implications for device modelling and physics

The behaviour and performance of GaN-based heterojunction field-effect transistors (HFETs) strongly depends on the parasitic resistances. This is especially true for AlGaN/GaN -based HFETs which often suffer from a current collapse here shown to be characterized by bias-dependent parasitics. In this work, we extract the source and drain resistances from S-parameter measurements under active operating biases. The bias dependence of the drain resistance supports the virtual gate hypothesis which attributes current collapse to a decreased 2DEG concentration in the gate-drain access region. Additionally, the bias dependence of the source resistance indicates a source-side resistance modulation at high gate biases. Extraction of the equivalent circuit from hot S-parameters yields better matching to measured data compared to more conventional ColdFET extraction. Using the intrinsic circuit parameters for the hot extraction, the average electron velocity was determined to be 1.9 × 107 cm/s. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)