Effect of Extended Defects on AlGaN Quantum Dots for Electron-Pumped Ultraviolet Emitters

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• AlGaN/AlN quantum dot (QD) superlattices exhibit high internal quantum efficiency (IQE) in the UV spectral range (230-300 nm).
• Bimodal emission, indicating multiple emission peaks, can arise from structural non-uniformities within these nanostructures.

Purpose of the Study:

• To investigate the origin of bimodal emission observed in AlGaN/AlN QD superlattices.
• To correlate structural defects with observed luminescence properties and quantum efficiency.

Main Methods:

• High-resolution microscopy techniques to analyze the morphology of QD superlattices.
• Photoluminescence spectroscopy to characterize emission properties.
• Schrödinger-Poisson calculations to model carrier behavior in QDs.

Main Results:

• Bimodal emission is linked to cone-like domains with deformed QD layers, originating at the AlN buffer/superlattice interface.
• These cones are associated with threading dislocations, causing shear strain and Ga enrichment at facets.
• Larger QDs are observed within the conic domains compared to the surrounding structure.

Conclusions:

• The observed bimodal luminescence is attributed to variations in QD size and composition within the cone-like domains and at their boundaries.
• Structural defects, specifically cone-like domains originating from dislocations, are the primary cause of emission bimodality in these AlGaN/AlN QD superlattices.