# Size-Dependent Emission Enhancement in Deep-Ultraviolet AlGaN Microrods

## TL;DR

This paper shows that smaller AlGaN microrods (2 μm) emit more deep-ultraviolet light than larger ones (4 μm), making them better for DUV applications.

## Contribution

The study introduces a size-dependent emission enhancement in high-Al-content AlGaN microrods, identifying 2 μm as the optimal diameter for maximum spontaneous emission.

## Key findings

- KOH treatment forms a-plane-dominated sidewalls on high-Al-content microrods.
- 2 μm microrods show a 3.76-fold enhancement in band-edge emission compared to 4 μm structures.
- CL mapping reveals radiative recombination dominates in smaller microrods.

## Abstract

High-Al-content AlGaN microrods represent an effective platform for engineering deep-ultraviolet (DUV) emission. Here, we fabricated AlGaN microrods with varying diameters (2, 3, and 4 μm) via a top-down approach involving inductively coupled plasma dry etching followed by a KOH wet chemical modification. Their crystallographic facets and size-dependent optical properties were systematically investigated using scanning electron microscopy (SEM), cathodoluminescence (CL) spectroscopy, and CL mapping. We found that the KOH treatment selectively forms a-plane-dominated sidewalls on the high-Al-content portion of the microrods, whereas the etch pit bottoms stabilize as m-plane facets. Notably, the CL spectra show that the band-edge emission intensity of the 2 μm microrods is enhanced by a factor of 3.76 compared to the 4 μm structures. CL mapping further unveils the competitive dynamics between radiative recombination within the quantum wells and non-radiative recombination at surface states. These findings pinpoint 2 μm as the optimal diameter among the investigated range for maximizing spontaneous emission from these high-Al-content AlGaN microrods.