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The Impact of AlN Spacer on Forward Gate Current and Stress-Induced Leakage Current (SILC) of GaN HEMT

A typical GaN HEMT forward gate current can be described by a simplified model, i.e., a Schottky diode with a parasitic resistance. This model, though, fails to fit certain GaN HEMT devices, noticeably those with AlN spacer. The Tsu-Esaki tunneling model with transfer matrix approach was used to investigate this phenomenon. The result shows that the forward gate current at low Vg is limited by Schottky interface as expected. At higher Vg, the AlN/GaN interface barrier gradually becomes dominant in deciding the gate current. This observation also reveals a discrepancy between measured and calculated gate current with an AlN spacer. Stress-induced leakage current (SILC) of this device type is investigated and the leakage current can be assigned to failure of the Schottky diode and/or the AlN/GaN interface using the back-to-back diode model. This model helps circuit designers to simulate RF performance under gate leakage condition.