Physical Modelling of the Kink Effect in Strained InGaAs/InAlAs pHEMTs

The InAlAs/InGaAs material system provides one of the highest transconductance pHEMT devices at a given gate size because of its large conduction band discontinuity, high electron mobility and very good carrier confinement in the channel. The DC characteristics, however, show a sudden rise in drain current at fixed value of drain voltage, resulting in high drain conductance and reduced voltage gain. This undesirable phenomenon is called Kink Effect. In this work a comprehensive understanding of the causes of this effect is developed using a 2-D physical device simulator. The modelled pHEMT is a layered structure that simulates the epitaxial layers of the fabricated device grown by MBE[1]. The developed model takes into account field dependent mobility, generation recombination mechanisms and deep-level traps are used. With the help of these physical models, threshold voltage, drain saturation and gate leakage current are successfully simulated and agree well with the measured results.