Characterization of ultrathin Al₂O₃ gate oxide deposited by RF-magnetron sputtering on gallium nitride epilayer on sapphire substrate

A systematic study was performed on Al₂O₃ films RF-magnetron sputtered on GaN substrate and subjected to different post-deposition annealing (PDA) temperatures (200–800 °C) in oxygen ambient. The as-deposited Al₂O₃ film and Al₂O₃ films subjected to PDA at 200 and 400 °C were present in amorphous phase and therefore undetectable by X-ray diffraction. By further enhancing the PDA temperature (≥600 °C), a transformation from amorphous to polycrystalline phase of Al₂O₃ happened. The increment of PDA temperature has contributed to an enhancement in leakage current density-electric field (J–E) characteristics of the investigated samples. A correlation between the acquired J–E characteristics with effective oxide charge, slow trap density, interface trap density, and total interface trap density were discussed. A detailed investigation on the conduction of charges through the as-deposited Al₂O₃ gate and Al₂O₃ gates subjected to different PDA temperatures via space-charge-limited conduction, Schottky emission, Poole–Frenkel emission, and Fowler–Nordheim tunneling were presented. - Highlights: • Post-deposition annealing (PDA) in oxygen ambient of Al₂O₃ films deposited on GaN. • Formation of crystalline Al₂O₃ films subjected to PDA at/beyond 600 °C. • J–E characteristics of Al₂O₃/GaN system are dependent on MOS characteristics. • Al₂O₃/GaN system was subjected to high temperature measurements. • Current conduction mechanisms governing the leakage current of Al₂O₃/GaN system