Morphology evolution and cathodoluminescence properties of non-polar aluminum nitride microwires

The aluminum nitride (AlN) one-dimensional microwires (UWs) are promising candidates for the achievement of highly efficient optoelectronic devices. Here, we report the successful synthetization of large-scale nonpolar AlN UWs without any catalysts using physical vapor transport (PVT). The growth direction of high-quality UWs is along m-orientation. The morphology of AlN UWs was examined by scanning electron microscopy (SEM), and they show a rectangular cross-section with a polyhedral tip. The tip of UW undergoes four morphological evolution driven by growth kinetics and free surface energy minimization. The unique cathodoluminescence (CL) patterns were found in the UW. Both sides of UW exhibit strong violet luminescence (345 nm). In contrast, other violet luminescence (320 nm) and blue luminescence (450 nm) were observed in the center of the UW. The evolution of the morphology of UW crystal suggests that the defect-related luminescence pattern may be related to the difference in impurity incorporation efficiency on a- and m-crystalline planes. The photoluminescence (PL) spectra were obtained and the Fabry–P é rot cavity mode in the microwire was demonstrated. The emission anisotropy of AlN may also contribute to the CL luminescence pattern of the microwires.