Surface passivation effects on AlGaN/GaN high-electron-mobility transistors with SiO2, Si3N4, and silicon oxynitride

Surface passivation effects were studied on AlGaN/GaN high-electron-mobility transistors (HEMTs) using ${\mathrm{SiO}}_2,$ ${\mathrm{Si}}_3{\mathrm{N}}_4,$ and silicon oxynitride (SiON) formed by plasma enhanced chemical vapor deposition. An increase of $I_{\mathrm{D}\max }$ and $g_{\mathrm{m}\max }$ has been observed on the passivated $({\mathrm{SiO}}_2,$ ${\mathrm{Si}}_3{\mathrm{N}}_4$ and SiON) HEMTs when compared with the unpassivated HEMTs. About an order of magnitude low $I_{\mathrm{gLeak}}$ and three orders of magnitude high $I_{\mathrm{gLeak}}$ was observed on ${\mathrm{Si}}_3{\mathrm{N}}_4$ and ${\mathrm{SiO}}_2$ passivated HEMTs, respectively, when compared with the unpassivated HEMTs. The increase of $I_{\mathrm{gLeak}}$ is due to the occurrence of surface related traps, which was confirmed by the observation of kink and hysteresis effect on dc and ac $I_{\mathrm{DS}}{\mathrm{–V}}_{\mathrm{DS}}$ characteristics, respectively. Though the ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivated HEMTs show better dc characteristics, the breakdown voltage ${\mathrm{(BV}}_{\mathrm{gd}})$ characteristics are not comparable with ${\mathrm{SiO}}_2,$ SiON passivated and unpassivated HEMTs. The SiON is also a very promising candidate as a surface passivant for AlGaN/GaN HEMTs because it shows better ${\mathrm{BV}}_{\mathrm{gd}}$ with low hysteresis width and small $I_D$ collapse than ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivated HEMTs.