Effects of O₂ Surface Treatment on Device Performance of AlGaN/GaN HEMTs with <i>In Situ</i> Crystalline SiN Cap Layer

This study demonstrates the impacts of O2 surface treatment (OT) process conditions on the AlGaN/GaN HEMTs with an in situ crystalline SiN cap layer. The effects of the O2 surface treatment on device performance, including off-state leakage, threshold voltage, on-state current, and breakdown voltage, are studied. By comparing O2 plasma treatments with three different power level process conditions of 100, 200, and 400 W, it is found that a moderate 100 W treatment power can effectively reduce device leakage current while increasing the device breakdown voltage to 890 V, which is about 10% higher than the untreated sample. TEM and XPS analyses confirmed that the crystalline SiN cap layer transformed into amorphous SiON after the O2 surface treatment, and the AlGaN barrier layer was also partially oxidized. The formation of SiON and partial oxidation of AlGaN lead to an increase in the height of the gate Schottky barrier and a weakening of the electric field along the gate-to-drain side, which is the reason for the decrease in the off-state leakage and the increase in the breakdown voltage of the device after the O2 surface treatment.