Singularity structures for sub-250 nm emissions from AlGaN-based semiconductors

Abstract Solid-state UV light sources emitting below a wavelength of 250 nm (far UVC) are expected in various application fields. Although III-nitride semiconductors are promising material systems for this purpose, their emission efficiency becomes lower at shorter wavelengths. In this paper, we review two emerging singularity structures, which can improve emission efficiency. One structure is AlGaN quantum wells (QWs) formed on macrosteps due to step bunching. Compared with the adjacent planar QWs on atomically flat terraces, QWs on macrosteps have lower Al compositions and thicker wells. Consequently, they act as potential minima. Strong emissions are observed from QWs on macrosteps due to suppressed nonradiative recombination. The other structure is GaN QWs with monolayer-level thickness. Strong carrier confinement within ultrathin GaN QWs enhances radiative recombination. Additionally, the exclusion of Al from the well decreases cation vacancies and lowers the nonradiative recombination probability.