Reverse Gate Leakage Induced Buffer Charging and Threshold Voltage Shift of GaN HEMTs

We discuss a physical mechanism in the AlGaN/GaN high electron mobility transistors (HEMTs) that partial electrons from reverse gate leakage (I g,off ) inject into the HEMT buffer and thereby shift the HEMT threshold voltage (Delta V-th). We analyze the A V th dependences on parameters including gate lengths, front barrier (FB) thickness, gate bias voltage, drain bias voltage, and the distance between the gate and the buffer. We specifically investigate the OFF-state stress with nonzero and zero Vds. The experiment with zero V ds helps identify the I (g,off) induced C doped GaN (C-GaN) charging; while the one nonzero V ds indicates a fast increase of C-GaN charging induced A V th with V-ds.. The A V th issue is significant for downscaled HEMTs with a short gate length and a close distance between the gate and the buffer. The issue is thus critical for downscaled HEMTs in high-speed RF applications. We propose a simple analytical expression for the A V- th and demonstrate methods to reduce the A V (th) .