Comparative study on performance of AlGaN/GaN MS-HEMTs with SiNx, SiOx, and SiNO surface passivation

A comparative investigation on device characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with SiNx, SiOx, and SiON passivation by using plasma enhanced chemical vapor deposition (PECVD) technique is conducted. The electrical performance of passivated GaN HEMTs are evaluated through DC current-voltage, pulsed current-voltage, and small-signal measurements. Obvious increases of 10.5% in drain current and of 8.6% in transconductance are observed for SiON passivated HEMT as compared with both the SiOx and SiNx passivated HEMTs. The SiOx passivated device is found to have lowest gate leakage current as well as off-state drain leakage current as compared to SiNx and SiON passivated devices. However, the pulsed I-V measurement shows a severe current collapse for SiOx passivated HEMT caused by the introducing of deep traps when compared with the SiNx and SiON passivated devices. Moreover, the small-signal measurement shows that the SiON passivated HEMT has a higher cut-off frequency due to the improvement in transconductance, which makes it a promising passivation layer for GaN based high power HEMT applications.