Evidence of surface states for AlGaN/GaN/SiC HEMTs passivated Si$_3$N$_4$ by CDLTS

In AlGaN/GaN heterostructure field-effect transistors (HEMTs) structures, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current and lowfrequency noise. This work demonstrates the effect of surface passivation on the current-voltage characteristics and we report results of our investigation of the trapping characteristics of Si$_3$N$_4$-passivated AlGaN/GaN HEMTs on SiC substrates using the conductance deep levels transient spectroscopy (CDLTS) technique. From the measured of CDLTS we identified one electron trap had an activation energy of 0.31 eV it has been located in the AlGaN layer and two hole-likes traps $H_1$, $H_2$. It has been pointed out that the two hole-likes traps signals did not originate from changes in hole trap population in the channel, but reflected the changes in the electron population in the surface states of the HEMT access regions.