High BFOM and threshold voltage stability in E-mode GaN HEMTs by using p-graded AlGaN cap layer

In this work, a high-performance E-mode Au free GaN high electron mobility transistor (HEMT) on Si featuring a p-graded-AlGaN cap layer is proposed. The device exploits the built-in polarization field induced by the graded-AlGaN cap layer and its superior interface quality to effectively mitigate gate-edge electric field crowding. With a gate-drain spacing (LGD) of 16 μm, the HEMT achieves a high breakdown voltage (VBR) of 1530 V (defined at ID = 10 μA/mm) and a low specific on-resistance (RON,sp) of 2.91 mΩ cm2, yielding a Baliga's figure of merit of 8.02 MW/mm2. This performance places the device among the highest values reported for conventional p-GaN gate HEMTs. Most importantly, the device exhibits exceptional threshold voltage (VTH) stability, with a minimal shift of 0.11 V at 175 °C and only 0.1 V drift under +7 V gate stress for 2000 s. This work validates an effective polarization-engineering strategy for developing high-breakdown, highly reliable GaN power devices for high-voltage applications.