Fixed-charge generation in SiO2/GaN MOS structures by forming gas annealing and its suppression by controlling Ga-oxide interlayer growth

A recent study has shown that anomalous positive fixed charge is generated at SiO2/GaN interfaces by forming gas annealing (FGA). Here, we conducted systematic physical and electrical characterizations of GaN-based metal-oxide-semiconductor (MOS) structures to gain insight into the charge generation mechanism and to design optimal interface structures. A distinct correlation between the amount of FGA-induced fixed charge and interface oxide growth indicated the physical origins of the fixed charge to be defect formation driven by the reduction of the Ga-oxide (GaO (x) ) interlayer. This finding implies that, although post-deposition annealing in oxygen compensates for oxygen deficiencies and FGA passivates defect in GaN MOS structures, excessive interlayer GaO (x) growth leads to instability in the subsequent FGA treatment. On the basis of this knowledge, SiO2/GaO (x) /GaN MOS devices with improved electrical properties were fabricated by precisely controlling the interfacial oxide growth while taking advantage of defect passivation with FGA.