Detrapping Kinetics in N-polar AlGaN/GaN MIS-HEMTs

We investigated the influence of aluminum concentration in the AlGaN cap layer on the stability of threshold voltage under gate and drain stress voltages. The devices examined are N-polar GaN MIS-HEMTs with a 2.6nm layer of Al
x
Ga
1-x
N cap under the gate contact. The devices have three different Al concentration (x=22%, x=34%, x=46%) in the AlGaN cap layer. DC measurements show that the devices with a higher Al concentration have a lower gate leakage current. In this work we found out: 1) the amount of threshold voltage shift during stress in these devices increases linearly with the value of gate leakage current at the different bias conditions 2) a higher Al percentage in AlGaN cap layer can suppress gate leakage current and thus reduce the instability of threshold voltage under high gate and drain filling voltages.