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

The effects of gate length L_G on breakdown voltage V_BR are investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) with L_G = 1 μm～ 20 μm. With the increase of L_G, V_BR is first increased, and then saturated at L_G=3 μm. For the HEMT with L_G=1 μm, breakdown voltage V_BR is 117 V, and it can be enhanced to 148 V for the HEMT with L_G = 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 L_G>3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with L_G = 3 μm～ 20 μm, and their breakdown voltages are in a range of 140 V-156 V.