Effects of SiO2 Passivation on Oxygen Annealed AlGaN/GaN HEMTs

We have investigated the effects of SiO2 passivation on the oxygen annealed AlGaN/GaN HEMTs. DC and pulsed I-V characteristics are analyzed to investigate the variation of trap level caused by SiO2 passivation and oxygen annealing. Both of oxygen annealing and SiO2 passivation are found to be effective methods to suppress the surface leakage current and increase the breakdown voltage of the AlGaN/GaN HEMTs. After an oxygen annealing, the leakage current is decreased from 621 μA/mm to 1.7 nA/mm when -5 V of VGS and -50 V of VDS are applied. However, the leakage current is increased to 5.7 μA/mm after SiO2 passivation on the oxygen annealed AlGaN/GaN HEMTs. The electron trapping through the deep trap is found to be dominant mechanism of the suppressed leakage current of the AlGaN/GaN HEMTs due to the low probability of the de-trapping from the deep trap to conduction band. SiO2 passivation suppresses the electron trapping through deep trap, which is produced by oxygen annealing. The breakdown voltage of conventional device without any treatment is 180 V. After oxygen annealing, the breakdown voltage is increased to 830 V while the AlGaN/GaN HEMT employing both of SiO2 passivation and oxygen annealing is 650 V.