Tetrahedral vs Spherical Nanocrystals: Does the Shape Really Matter?

Tetrahedral nanocrystals (NCs) have emerged as promising structures whose shape can prove advantageous over the more conventional spherical structure, notably in the superior stability it affords in the growth of III-V nanostructures. However, it is still not clear in what other properties they differ from their spherical counterparts. It has been shown experimentally that the position of the first exciton peak in some materials is very different between spherical and tetrahedral dots of the same size. In spite of this evidence, however, in the absence of accurate theoretical sizing curves obtained specifically for tetrahedra, their size is, nevertheless, often estimated based on emission curves relative to spherical dots instead. Here, we provide a comprehensive theoretical characterization of tetrahedral nanocrystals made of technologically relevant Cd-based and In-based materials, including much needed bespoke calibration curves, band edge positions, and the size dependence of radiative recombination times, for side lengths ranging from similar to 3 to over 8 nm, corresponding to structures containing from about 300 to over 3300 atoms. We also present a side-by-side comparison with the properties of nominally spherical NCs made of the same materials, as a function of both volume and confinement size, highlighting differences and similarities between the two types of structures, which are analyzed in terms of shape, degree of confinement, and number of facets. Our results will contribute to a better understanding of the properties of these versatile shapes and, by clarifying the differences with those of spherical nanostructures, enable a clear identification of the respective ideal application range for an effective and more tailored device exploitation.