Interface characterization of ALD deposited Al₂O₃ on GaN by CV method

Abstract

Abstract A high dielectric interface quality is the determining factor for high power GaN metal oxide semiconductor field‐ effect transistor (MOSFET) devices. We characterized 100 Å thick aluminum oxide (Al 2 O 3 ) films deposited by ALD on MOCVD grown undoped GaN on sapphire. First we measured the leakage current and densification behaviour of the dielectric after annealing at different temperatures up to 900 °C and determined the polycrystalline phase change to be around 800 °C. Further we characterized the interface charges of both films according to the flatband shift, induced by over‐band gap UV light, showing the lowest interface charge density of 1.27 × 10 11 cm –2 after thermal treatment at 850 °C. Additionally, we measured the AC conductivity and calculated the interface states density (Dit) of the upper half of the GaN bandgap, showing the lowest Dit of around 2×10 10 cm –2 eV –1 at 2 eV above the valence band, while it remains higher around the band edge at 2.8×10 11 cm –2 eV –1 , after annealing at 750 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)