Effect of gate length on breakdown voltage in AlGaN/GaN high-electron-mobility transistor*

The effects of gate length LG on breakdown voltage VBR are investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) with LG = 1 μm~ 20 μm. With the increase of LG, VBR is first increased, and then saturated at LG = 3 μm. For the HEMT with LG = 1 μm, breakdown voltage VBR is 117 V, and it can be enhanced to 148 V for the HEMT with LG = 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage. A similar suppression of the impact ionization exists in the HEMTs with LG > 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG = 3 μm~20 μm, and their breakdown voltages are in a range of 140 V–156 V.