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 V
_g
is limited by Schottky interface as expected. At higher V
_g,
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.