Cone-shaped defects on AlGaN quantum dots for electron-beam pumped UV-emitters

One alternative to the challenges posed by AlGaN LEDs is the use of electron-beam pumped lamps based on AlGaN quantum dot (QD) superlattices (SLs). This approach offers the advantage of circumventing the challenging p-type doping and contacts of AlGaN, while providing a large active region. Previous reports from our group demonstrated UVC-emitting AlGaN QD-SLs grown by plasma-assisted molecular beam epitaxy with internal quantum efficiency in the range of 50% [1]. However, the samples still exhibit spatial inhomogeneities and relatively wide (between ~10 and ~20 nm ) emission lines, sometimes with multi-peak structure. In this contribution, we delve into the origin of bimodal emission in AlGaN/AlN QD superlattices in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-shaped defects originating at the AlN buffer/superlattice interface and propagating vertically. These defects are associated with a dislocation that produces strong shear strain, which favors the formation of 30° faceted pits. The cone-like structures present Ga enrichment at the boundary facets and larger QDs within the defect. The bimodality is attributed to the differing QD size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schrödinger-Poisson calculations [2].<br/>[1] J. Cañas et al., under review. arXiv:2305.15825 <b>2023</b>. https://doi.org/10.48550/arXiv.2305.15825<br/>[2] J. Cañas et al., under review. arXiv:2310.04201 <b>2023</b>. https://doi.org/10.48550/arXiv.2310.04201