Variation of Dominant Degradation Mechanism in AlGaN Barrier Layer With Different Voltage Stress on the Gate of AlGaN/GaN High Electron Mobility Transistors

Abstract

This letter proposes that dominant mechanism that induces the change of traps and defects in AlGaN barrier layer varies with different range of voltage stress on the gate of AlGaN/GaN high electron mobility transistors. The gate-source (drain) reverse current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured after each voltage stress applied to the gate which stepped from -8 to -70 V in -1 V step. They showed similar changes in test, both decreased from -8 to -20 V and increased from -20 to -70 V. The micro-Raman spectroscopy focused on GaN layer was measured before stress, during -30 V stress, and after -70 V stress, respectively. They kept constant in the measurement. It proved that inverse piezoelectric effect had few influence in GaN layer. The increase of filled inherent traps and permanent defects in AlGaN barrier layer after different voltage stress accounted for the experimental phenomenon. The former was due to gate electron injection which played a main role in low bias stage, the latter was due to inverse piezoelectric effect which played a main role in high bias stage.