Effect of extended defects on AlGaN QDs for electron-pumped UV-emitters

TL;DR

This paper investigates how extended defects influence bimodal emission in AlGaN quantum dot superlattices, revealing defect-related structural and compositional factors that cause dual emission peaks in UV-emitters.

Contribution

It identifies the origin of bimodal emission as defect-induced variations in quantum dot size and composition, linking structural defects to optical properties in AlGaN QD systems.

Findings

Defects originate at the AlN buffer/superlattice interface and propagate vertically.

Bimodal emission is caused by differences in dot size and composition within defects.

Defect structures include cone-like features with Ga enrichment and larger QDs.

Abstract

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like defects starting at the first 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{\deg} 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 dot size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schr\"odinger-Poisson calculations.