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 LG = 1 mu m similar to 20 mu m. With the increase of L-G, V-BR is first increased, and then saturated at L-G = 3 mu m. For the HEMT with L-G = 1 mu m, breakdown voltage V-BR is 117 V, and it can be enhanced to 148 V for the HEMT with L-G = 3 mu m. The gate length of 3 mu m can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 mu m, 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 mu m. As a result, there is no obvious difference in breakdown voltage among the HEMTs with L-G = 3 mu m similar to 20 mu m, and their breakdown voltages are in a range of 140 V-156 V.