Analytical modelling of drain-current characteristics of AlGaN/GaN HFETs with full incorporation of steady-state velocity overshoot

An analytical model for drain-current characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs), with incorporation of steady-state velocity overshoot and the inflection points in the electronic drift-transport characteristics, is presented. Manifestations of these transport characteristics are usually neglected in modelling the drain current of III-V HFETs. However, significance of these features in AlGaN/GaN material system, compared with other III-V technologies, requires re-evaluation of this policy. Although, for the current state of the art these features are partially masked by the parasitic features such as the drain and source contact resistance, through further improvement in the device fabrication technology they will deserve further attention. The wide peak and pronounced inflection points in the transport characteristics of AlGaN/GaN heterojunctions are modelled through considering a drift-diffusion channel rather than a drift-only transport channel. Simulation results are compared with a non-diffusion type channel that has been so far assumed in modelling the drain current of these devices. Results of the presented model indicate the role of drift-velocity overshoot in further increasing the maximum drain current of AlGaN/GaN HFETs, as the contact resistance is reduced. Comparisons with the experimental measurements are also provided.