Analysis of high-k passivation-layer effects on buffer-related breakdown and current collapse in AlGaN/GaN HEMTs

We analyze breakdown characteristics and current collapse in AlGaN/GaN HEMTs, with the passivation layer's relative permittivity ε_r as a parameter. It is shown that the off-state breakdown voltage is considerably enhanced by introducing a high-k passivation layer because the electric field at the drain edge of the gate is weakened and the buffer leakage current is reduced. The breakdown voltage in the high-ε_r region increases when the gate voltage is changed from -8 to -10 V, because the buffer leakage current is reduced. It is also shown that drain lag and current collapse in AlGaN/GaN HEMTs could be reduced by introducing a high-k thick passivation layer, because the electric field at the drain edge of the gate is reduced, leading to less electron injection into the buffer layer and weaker buffer trapping effects.