Experimental evidence of the existence of multiple charged states at Al2O3/GaN interfaces

Abstract

The electrical properties of metal-oxide-semiconductor (MOS) capacitors with Al2O3/GaN interfaces formed by atomic layer deposition at various deposition temperatures (Td) were systematically investigated through comparison with the interface properties of a Si MOS capacitor. Although interface trap densities (Dit) for the GaN MOS capacitors are almost the same as for the Si MOS capacitor, surface potential fluctuation (σs) for the GaN MOS capacitors formed at various Td are much larger than for the Si MOS capacitor. Comparison between a theoretical calculation related to σs and the measured results clarified that the energy dependences of σs in the bandgap of GaN cannot be explained by electron trapping to the interface traps with the single acceptor nature (0/−). We found that the result is experimental evidence of the existence of multiple charge states at the Al2O3/GaN interfaces. The existence of multiple charge states suggests that it may be difficult to obtain good carrier transport in future GaN devices with a MOS structure.