Effects of Dielectric Passivation on Device Performance of AlGaN/GaN High-Electron-Mobility Transistors

Various dielectrics deposited on the surfaces of AlGaN/GaN-based metal-gate high-electron-mobility transistors (HEMTs) were investigated to understand their effects on the device characteristics. The observed increase by 30% in the two-dimensional electron gas (2DEG) sheet carrier density by the deposition of SiO2, Si3N4, or Al2O3 was in line with the improved output and transfer characteristics of the HEMT devices with the deposited dielectrics, as compared to those of the bare HEMT device without dielectric. The improvements seemed to result from the strain accumulation in AlGaN due to the difference in thermal expansion between AlGaN and the dielectric and from the effective treatment of surface electrical passivation by the deposited dielectric. Furthermore, suppression of current collapse was observed in the SiO2- and Si3N4-deposited samples, as compared to the bare HEMT device.