Demonstration of Ultra Low 2DEG Sheet Resistance Using Al-Enriched AlGaN Layer in the AlXGa1-XN/AlN/GaN Heterojunction

Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) based on a bi-dimensional electron gas (2DEG) are essential components in many electronic applications. A crucial aspect involves minimizing the sheet resistance of the 2DEG to reduce the total on-state resistance of the device. In this study, we explored AIGaN layers with high aluminum content ranging from 0.24 to 0.60. We report significantly low 2DEG sheet resistance of $213 \Omega / \square$ at $25^{\circ} \mathrm{C}$ and $455 \Omega / \square$ at $150^{\circ} \mathrm{C}$ for the $\mathrm{Al}_{0.6} \mathbf{G a}_{0.4} \mathrm{~N} / \mathrm{AIN} / \mathrm{GaN}$ heterojunction, induced by a higher electron density ($\mathrm{n}_{\mathrm{s}}$), and despite a decrease in mobility with higher aluminum content ($\mu_{2 \mathrm{DEG}}$). The increase of the 2DEG density with the highest aluminum molar concentration is explained by a reduced polarization charge at the $\mathrm{Al}_{\mathrm{x}} \mathrm{Ga}_{1-\mathrm{x}} \mathrm{N} / \mathrm{AIN}$ interface, and it is validated by 1D Poisson-Schrödinger simulations.