**5. Conclusion**

In summary, an innovative scheme with a vertical short gate structure in GaN-based HEMTs to realize normally-off operation is proposed and verified by TCAD simulations. The VG-HEMT exhibits a large Vth of 3.1 V and an improved output current density and Ron, which can greatly reduce the power loss of the device. Furthermore, the VG-HEMT displays a lower leakage current during the off state owing to the more uniform electric field distribution by reducing the peak electric field to 26% of the LG-HEMT case. The quantitative dependence of saturated current density and Ron on the scattering factors in the trenched vertical gate channel was investigated in detail which concludes the benefit of the proposed short vertical gate VG-HEMT scheme. Although the fabrication process of the VG-HEMT might be complicated and time-consuming, the device structure is proposed for the first time and does have several advantages. More improved performances will be achieved and demonstrated in the following experiments.

**Author Contributions:** Writing—Original Draft, Z.S.; Investigation, N.S.; Validation, P.T.; Data Curation, C.Z.; Software, Y.C.L.; Writing—Review & Editing, H.H.

**Funding:** This research was funded by the National Natural Science Foundation of China under Grant Nos. 61971090 and 51607022, the Open Project Program of the Key Laboratory of Semiconductor Materials Science under Grant No. KLSMS-1804 and the Open Project Program of the Key Laboratory of Nanodevices and Applications under Grant No. 18JG02 from the Chinese Academy of Sciences.

**Conflicts of Interest:** The authors declare no conflict of interest.
