Electrical properties and energy band alignment of SiO₂/GaN metal-oxide-semiconductor structures fabricated on N-polar GaN(000(1)over-bar) substrates

The interface properties and energy band alignment of SiO2/GaN metal-oxide-semiconductor (MOS) structures fabricated on N-polar GaN(000 (1) over bar) substrates were investigated by electrical measurements and synchrotron-radiation x-ray photoelectron spectroscopy. They were then compared with those of SiO2/GaN MOS structures on Ga-polar GaN(0001). Although the SiO2/GaN(000 (1) over bar) structure was found to be more thermally unstable than that on the GaN(0001) substrate, excellent electrical properties were obtained for the SiO2/GaN(000 (1) over bar) structure by optimizing conditions for post-deposition annealing. However, the conduction band offset for SiO2/GaN(000 (1) over bar) was smaller than that for SiO2/GaN(0001), leading to increased gate leakage current. Therefore, caution is needed when using N-polar GaN(000 (1) over bar) substrates for MOS device fabrication.