Influence of GaN Stress on Threshold Voltage Shift in AlGaN/GaN High-Electron-Mobility Transistors on Si under Off-State Electrical Bias

The change in threshold voltage (Vth) in AlGaN/GaN high-electron-mobility transistors (HEMTs) on Si occurs during off-state bias stress. Raman spectroscopy shows that the GaN strain/stress changes with the increase in buffer and i-GaN thicknesses. Our results revealed that there is a strong correlation between the Vth shift and GaN strain/stress. The Vth shifts positively and negatively, respectively, for biaxial tensile and compressive strains. We observed minimal device degradation with the negligible Vth shift before and after off-state bias stress for the strain relieved sample. The results illustrate the importance of GaN strain/stress for the degradation and reliability of AlGaN/GaN HEMTs.