Analytical Models for the 2DEG Density, AlGaN Layer Carrier Density, and Drain Current for AlGaN/GaN HEMTs

Here, we report a unified analytical model for the 2-D electron gas density (<inline-formula> <tex-math notation="LaTeX">${n}_{S}$ </tex-math></inline-formula>) in AlGaN/GaN HEMTs, considering the carriers induced in the AlGaN layer (<inline-formula> <tex-math notation="LaTeX">${n}_{B}$ </tex-math></inline-formula>) to satisfy charge balance at high gate bias. To extend the validity of our model for gate voltages below the off voltage, we have merged a popular subthreshold model to our model using an interpolation function. Our model for <inline-formula> <tex-math notation="LaTeX">${n}_{B}$ </tex-math></inline-formula> is fully analytical, without any explicit dependence on <inline-formula> <tex-math notation="LaTeX">${n}_{S}$ </tex-math></inline-formula>, and is a function only of the gate voltage, which to the best of our knowledge, is the first such report. The model results show a very good match with published results and experimental data reported in the literature. These models are subsequently used in a charge-based drain current model, developed under the drift-diffusion framework. In order to make our model valid for small-dimension devices, several second-order effects have been included in our drain current model. The model results for the drain current show an excellent match with the experimental data reported in the literature, for channel length varying from <inline-formula> <tex-math notation="LaTeX">$1~\mu \text{m}$ </tex-math></inline-formula> to 125 nm. Also, it shows the first-order continuity of the drain current with respect to the bias voltages, thus making it suitable for use in circuit simulators.

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