Interface characteristics of spin-on-dielectric SiOx-buffered passivation layers for AlGaN/GaN high electron mobility transistors

•Spin-on-dielectric (SOD)-buffered passivation for AlGaN/GaN HEMTs•Characterize the charge density and interface states using the C–V measurements•SOD-buffered passivation minimizes surface states at the interface.•DC performance of SOD-buffered structure is due to the interface characteristics.

To reveal the cause for significant enhancement of dc current performance of the AlGaN/GaN high electron mobility transistors (HEMTs) with the spin-on-dielectric (SOD) SiOx-buffered passivation structure compared to the conventional Si3N4 passivation deposited by plasma-enhanced vapor deposition (PECVD), we characterized the passivation interfaces using the cross-sectional transmission electron microscopy, cathodoluminescence, capacitance–voltage (C–V) characterizations, and Hall-effect measurements. The interface state density of PECVD Si3N4 passivation was in the range of 1012–1013 cm− 2 eV− 1, which is one-order higher than that of the SOD (1011–1012 cm− 2 eV− 1) as measured by C–V measurements from the metal–insulator–semiconductor capacitors. Higher density of effective oxide charge density (especially dominant contribution of ionic mobile charge) was also derived from the PECVD Si3N4 passivation. A well-resolved reduction of the electron Hall mobility of the Si3N4 passivation compared to that of the perhydropolysilazane SOD passivation, which can be due to the higher-density interface states and trap charges, can answer the relative dc current collapse of our HEMT devices.