Effects of SiO₂passivation on the sheet carrier density of two-dimensional electron gas formed in the AlGaN/GaN interface

Increasing the thickness of the SiO2 dielectric layer used to electrically isolate AlGaN/GaN high-electron-mobility transistors led to a gradual increase in the sheet carrier density of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. An increase of approximately 33% in sheet carrier density was observed after depositing 125 nm of SiO2 by plasma-enhanced chemical vapor deposition. The observed dependency of the sheet carrier density in 2DEG on SiO2 thickness was attributed to strain accumulation to AlGaN and improved surface passivation effect, based on analyses by Raman spectroscopy and dielectric capacitance measurement.