Multi-wavelength emission through self-induced defects in GaZnO microrods

Multi-wavelength emission in wide bandgap semiconductors is commonly achieved through ternary alloying or quantum size effects. However, multi-wavelength emission within a single microstructure is highly challenging using these approaches. Here, we demonstrate that the luminescence wavelength within individual GaZnO microrods can be tailored via defect engineering. Fast chemical vapor growth of oxygen-rich ZnO microrods with Ga₂O₃ as an additive in the ZnO vapour leads to formation of a tapered morphology with graded distribution of Ga dopants, while the Ga incorporation does not significantly alter their crystal structure. With increasing Ga content from 1 to 6 at% from tip to base, the GaZnO microrods increase in diameter towards the substrate in accordance with the birth-and-spread mechanism. The local near-band-edge emission within single ZnO microrods, analyzed by nanoscale cathodoluminescence spectroscopy, exhibits a red shift of ~0.6 eV with increasing Ga content and exhibits signature characteristics of an excitonic emission. Density Functional Theory calculations reveal that the variation in the emission wavelength arises from bandgap narrowing due to the merging of the electronic states of Ga defect complexes with ZnO energy bands. The experimental and theoretical results demonstrate (i) the utility of using the self-regulation of defect compensation effects for band gap engineering and (ii) the possibility of multi-wavelength light sources within individual microrods.