Effect of SiO2 surface passivation on the performance of GaN polarization superjunction heterojunction field effect transistors

In this article, the effects of the SiO2 surface passivation layer are reported on normally-on 1.2 kV GaN polarization superjunction (PSJ) heterojunction field effect transistors (HFETs) by comparing the electrical performances of PSJ HFETs with and without SiO2 surface passivation. A slight recovery of the 2D electron gas sheet density is observed in the slight negative shift of Vth after SiO2 surface passivation. Passivation also increases the breakdown voltage. This improvement may result from removing positive surface charges in defects along the P-GaN gate sidewall and top u-GaN layer after the specifically designed SiO2 surface passivation. Furthermore, the SiO2 surface passivation can also effectively suppress the surface gate leakage currents in the PSJ HFETs by eliminating the conductive channel created by the positive surface charges in defects.