We study the origin of interfacial shallow hole traps appearing in GaN-based metal oxide-semiconductor field-effect transistors (MOSFETs) using density-functional-theory calculations with realistic interfacial models. It is demonstrated that the ${\mathrm{GaO}}_x$ interfacial layer spontaneously formed at the ${\mathrm{GaN}/\mathrm{SiO}}_2$ interfaces, even without conventional point defects such as oxygen vacancies, induces hole traps. The holes are directly trapped at the tail state of amorphous ${\mathrm{GaO}}_x$, which are shown here to consist of $2p$ orbitals of low-coordinated O atoms with relatively high electrostatic potential. When occupied, these states are located just below the GaN valence band maximum, but upon hole localization, they are raised to the mid-gap region and become hole traps as a result of the lengthening of the Ga–O bonds.

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• Defects
• MOSFET
• Hybrid functionals