Size-Dependent Emission Enhancement in Deep-Ultraviolet AlGaN Microrods

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.