| Summary: | We employed the local p-doped region with a concentration of 3 × 10<sup>16</sup> cm<sup>−3</sup>, 5 × 10<sup>16</sup> cm<sup>−3</sup> and 7 × 10<sup>16</sup> cm<sup>−3</sup> in the back-barrier of full-AlGaN high electron mobility transistors (HEMTs). Further enhancement of the breakdown voltage (BV) with less influence on drain–current density (I<sub>D</sub>) is demonstrated. The 2D simulation results show that the BV increases with the doping concentration due to the weakening of the electric field. Compared with the traditional Al<sub>0.18</sub>Ga<sub>0.82</sub>N back-barrier structure, p-type doping with the concentration of 7 × 10<sup>16</sup> cm<sup>−3</sup> in the back-barrier layer can reduce the peak electric field by 3.06 × 10<sup>5</sup> V/cm, so that the BV is increased by about 11%, when the maximum drain–current density (I<sub>Dmax</sub>) of the device is maintained at 717.8 mA/mm. Furthermore, the BV is closely connected to the geometric characteristics of the local p-doped region. The optimal distance between the doped region and the channel is found to be 150 nm for the doping concentration of 7 × 10<sup>16</sup> cm<sup>−3</sup>. The length of the doped region and the distance between the region and the drain is also found to vary linearly with the BV of the device.
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