Investigation of Surface- and Buffer-Induced Current Collapse in GaN High-Electron Mobility Transistors Using a Soft Switched Pulsed Measurement

In this letter, we investigated the behaviors of surface- and buffer-induced current collapse in AlGaN/GaN high-electron mobility transistors (HEMTs) using a soft-switched pulsed I-V measurement with different quiescent bias points. It is found that the surface- and buffer-related current collapse have different relationship with the gate and drain biases (V_GS0,V_DS0) during quiescent bias stress. The surface-induced current collapse in devices without passivation monotonically increases with the negative V_GS0, suggesting that an electron injection to the surface from gate leakage is the dominant mechanism and the Si₃N₄ passivation could effectively eliminate such current collapse. The buffer-induced current collapse in devices with intentionally carbon-doped buffer layer exhibits a different relationship with V_GS0 after surface passivation. The buffer-related current collapse shows a bell-shaped behavior with V_GS0, suggesting that a hot electron trapping in the buffer is the dominant mechanism. The soft-switched pulsed I-V measurement provides an effective method to distinguish between the surface- and buffer-related current collapse in group III-nitride HEMTs.