Small valence band offset of h-BN/Al0.7Ga0.3N heterojunction measured by X-ray photoelectron spectroscopy

Abstract

Because of its large bandgap of ∼6.0 eV and suitability for high p-type doping, hexagonal boron nitride (h-BN) has become a candidate material that can serve as a p-layer by forming a heterostructure with AlGaN materials with a high Al fraction in deep-ultraviolet optoelectronic devices. The band offsets at the heterojunction are crucial to the device design because they determine the hole and electron transport properties across the heterojunction. In this study, we give the band alignment between h-BN and Al0.7Ga0.3N using the valence and conduction band offsets. The valence band offset of the h-BN/Al0.7Ga0.3N heterojunction is determined via X-ray photoelectron spectroscopy (XPS) to be as small as −0.01 ± 0.09 eV. The small valence band discontinuity that occurs at the h-BN/Al0.7Ga0.3N interface is further confirmed using angle-resolved valence band spectra from the XPS measurements. By combining the bandgap values of Al0.7Ga0.3N and h-BN which were estimated using absorption spectra measurements, the conduction band offset is found to be approximately 0.89 ± 0.09 eV. These results indicate that h-BN is an excellent material for hole injection into Al0.7Ga0.3N. Meanwhile, the electrons can be effectively blocked away from h-BN. These results will be helpful in the design of group-III-nitride-based optoelectronic devices, particularly deep-ultraviolet light-emitting diodes and lasers.