  The effect of a two dimensional (2D) graphene layer (GL) on top of the
silicon nitride (SiN) passivation layer of AlGaN/GaN
metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs)
has been systematically analyzed. Results showed that in the devices without
the GL, the maximum drain current density (I_D,max) and the maximum
transconductance (g_m,max) decreased gradually as the mist exposure time
increased, up to 23% and 10%, respectively. Moreover, the gate lag ratio (GLR)
increased around 10% during mist exposure. In contrast, devices with a GL
showed a robust behavior and not significant changes in the electrical
characteristics in both DC and pulsed conditions. The origin of these behaviors
has been discussed and the results pointed to the GL as the key factor for
improving the moisture resistance of the SiN passivation layer.
