Study on the electrical degradation of AlGaN/GaN MIS-HEMTs induced by residual stress of SiNx passivation

In this paper, we report a new phenomenon in C-V measurement of different gate length MIS-HEMTs, which can be associated with traps character of the AlGaN/GaN interface. The analysis of DC measurement, frequency dependent capacitance-voltage measurements and simulation show that the stress from passivation layer may induce a decrease of drain output current Ids, an increase of on-resistance, serious nonlinearity of transconductance gm, and a new peak of C-V curve. The value of the peak is reduced to zero while the gate length and measure frequency are increasing to 21 μm and 1 MHz, respectively. By using conductance method, the SiNx/GaN interface traps with energy level of EC−0.42 eV to EC−0.45 eV and density of 3.2 × 1012 ∼ 5.0 × 1012 eV−1 cm−2 is obtained after passivation. According to the experimental and simulation results, formation of the acceptor-like traps with concentration of 3 × 1011 cm−2 and energy level of EC−0.37 eV under the gate on AlGaN barrier side of AlGaN/GaN interface is the main reason for the degradation after the passivation.