Effect of surface passivation on performance of AlGaN/GaN/Si HEMTs

Abstract

Performance of intentionally undoped and doped AlGaN/GaN/Si high electron mobility transistors (HEMTs) before and after passivation with SiO 2 and Si 3N 4 is investigated. Hall effect measurements show higher impact of Si 3N 4 than SiO 2 passivation on the carrier concentration increase in the channel. Improvements in DC performance of HEMTs after passivation with SiO 2 and Si 3N 4 correspond to the changes in sheet carrier concentration. Small signal microwave characterisation shows a decrease (from 18.6 to 9 GHz) and an increase (from 18.4 to 28.8 GHz) of the current gain cut off frequency after SiO 2 and Si 3N 4 passivation, respectively. Similar effect of passivation is found in microwave power changes––only about a half of the power is obtained after SiO 2 passivation but more than doubled power results from Si 3N 4 passivation, measured at 2 GHz. Higher density of interface states for SiO 2 than Si 3N 4 passivation is supposed to be responsible for these effects. However, for an optimal design of GaN-based power devices additional studies related to the interface between a passivation layer and GaN are needed.