Insight into traps at Al2O3/p-GaN metal-oxide-semiconductor interface fabricated on free-standing GaN substrate

Highlights: • The interface traps at the homoepitaxial p-GaN MOS interfaces are systematically investigated. • The impedance spectroscopy is utilized to analyze the p-GaN MOS capacitors by fitting the proposed equivalent circuits. • The hysteresis in both current-voltage and capacitance-voltage properties are markedly suppressed, due to the reduction of the interfacial disorders. -- Abstract: Vertical electronic devices fabricated from GaN-on-GaN substrate have been attracting growing interest due to their large current capacity and high breakdown voltage. However, the traps at the p-GaN metal-oxide-semiconductor (MOS) interfaces have been rarely understood. Here, the electrical characteristics of the Al₂O₃/p-GaN MOS structures fabricated on the free standing GaN substrates are investigated. The hysteresis in both current-voltage and capacitance-voltage curves are markedly reduced compared to the p-GaN MOS device fabricated on the sapphire substrate due to the suppression of the interfacial disorders, while a frequency dispersion is still observed. The interface state density is reduced from 7 × 10¹² to 2 × 10¹² cm⁻²eV⁻¹ and the border trap density is reduced from 1.3 × 10¹³ to 2.2 × 10¹² cm⁻². The mechanism of the frequency dispersion is clarified by the impedance spectroscopy analysis. It reveals that the interface traps play an important role in the accumulation region of the capacitance-voltage property, and in the depletion region the leakage current induced shunt resistance dominates the non-ideal electrical properties.