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 SiO2, Si3N4, and silicon oxynitride (SiON) formed by plasma enhanced chemical vapor deposition. An increase of I-Dmax and g(mmax) has been observed on the passivated (SiO2, Si3N4 and SiON) HEMTs when compared with the unpassivated HEMTs. About an order of magnitude low I-gLeak and three orders of magnitude high I-gLeak was observed on Si3N4 and SiO2 passivated HEMTs, respectively, when compared with the unpassivated HEMTs. The increase of I-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-DS-V-DS characteristics, respectively. Though the Si3N4 passivated HEMTs show better dc characteristics, the breakdown voltage (BVgd) characteristics are not comparable with SiO2, 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 BVgd with low hysteresis width and small I-D collapse than Si3N4 passivated HEMTs. (C) 2004 American Institute of Physics.