Surface passivation effects in AlGaN/GaN HEMTs on high-resistivity Si substrate

AlGaN/GaN high-electron-mobility transistors (HEMTs) were successfully fabricated on high- resistivity (HR) Silicon substrate. Surface passivation effects on AlGaN/GaN HEMTs were studied using Si₃N₄ dielectric layer grown by plasma enhanced chemical vapor deposition. The device direct-current current-voltage (I_DS-V_DS) characteristics, pulsed I_DS-V_DS characteristics, microwave small-signal and large-signal characteristics were studied before and after passivation. An enhancement of drain current (I_D) density and the extrinsic transconductance was observed for the devices with full Si₃N₄ passivation. An improvement of f_T, f_max and device output power (P_out) was also observed after surface passivation. A new evaluation method implemented to identify the I_D collapse related traps from AlGaN/GaN HEMTs. More than 80% of I_D collapse suppression and 80% of increase in P_out were observed in AlGaN/GaN HEMTs by Si₃N₄ passivation. The P_out increase in AlGaN/GaN HEMTs by surface passivation is in good agreement with the I_D collapse suppression in AlGaN/GaN HEMTs by surface passivation.