Exploring the Shape-Dependent Optical Properties of Tetrahedral Semiconductor Nanocrystals

Over the last four decades, the size-dependent photophysical characteristics of quantum dots (QDs) have been extensively studied through the quantum confinement effect, typically described by the three-dimensional particle-in-a-box equation assuming a spherical shape with infinite potential barriers. While the shape effect in spatially confined charges and excitons has been extensively investigated for anisotropic semiconductor nanocrystals, QDs with specific shapes remain relatively underexplored. In this talk, we present a synthetic strategy to achieve tetrahedral semiconductor nanocrystals with high shape homogeneity. Notably, the sizing curve of tetrahedral semiconductor nanocrystals with well-defined facets reveals an unconventionally smaller band gap compared to spherical QDs of equivalent volume. We suggest that upon ligand passivation, the (111) in-gap state significantly hybridizes with the bulk conduction band minimum (CBM) and remains at CBM, resulting in a reduced band gap, especially when the bulk bandgap is small. This unique surface-originated quantum confinement effect positions tetrahedral InAs QDs at lower energies in the sizing curve. Conversely, tetrahedral InP QDs, with a relatively larger band gap, exhibit opposite trends in the sizing curve, which can be explained by the particle-in-a-box model based on previous understandings. Finally, we fabricate photodetectors utilizing these materials and demonstrate their enhanced performance in terms of specific detectivity and response time, showing the potential of tetrahedral nanocrystals in advanced optoelectronic applications.