Hexagonal SiGe Quantum Dots in Nanowires.

Group IV materials, such as Si and Ge, are widely used in quantum information devices due to their CMOS compatibility and excellent transport properties. However, their indirect band gaps hinder optical spin control such as initialization or readout via photons. In this work, we establish a pathway toward optically addressable group IV quantum dots, realizing them in SiGe with a hexagonal crystal structure. This material benefits from a direct band gap with wavelength emission that is tunable through the Ge content. The hexagonal SiGe quantum dots are realized here as axial heterostructures within branched nanowires, enabling precise geometric control and a high crystal quality. Nanometer-sharp heterointerfaces are achieved without defect formation, indicating a fully elastic relaxation of the lattice mismatch. Geometric phase analysis and computational simulations validate this behavior. These results show the feasibility of hexagonal SiGe quantum dots, providing a promising platform for integrating optical control into group IV quantum architectures.