Device Modeling of Graded III-N HEMTs for Improved Linearity

When GaN HEMTs are used in power amplifier applications, their performance falls well short of ideal due to power-gain roll-off that results from having a peaked transconductance characteristic. A promising design solution involves compositionally grading the channel, and we here formulate a numerical device model to explore this approach that couples linear electroelasticity, diffusion-drift transport with new mobility models, and density-gradient theory. Lumped modeling of the large-signal behavior is also developed to explore the power amplifier performance. Preliminary results presented here indicate that the graded-channel idea has value, especially for gate lengths greater than about 100nm.