Colloidal synthesis, physical properties, and applications of zero- and one-dimensional GeSn nanostructures

Although germanium (Ge) is a semiconductor frequently used in many facets of materials science, its optical applications are limited because of an indirect band structure, which significantly diminishes absorption and emission efficiency. However, sufficiently high levels of tin (Sn) alloying enable an indirect-to-direct band structure crossover, resulting in improved optical properties. Moreover, the bandgap of GeSn alloys can be tuned by simply varying the alloy composition; therefore, the material can be modified for compatibility with silicon (Si) based electronics. While lattice mismatch makes the solubility of Sn in Ge extremely low in bulk alloys (<1%), metastable nanoalloys produced under nonequilibrium conditions show minimum to no lattice strain, allowing the synthesis of GeSn nanoalloys with wider tunability of Sn (up to 95%). Furthermore, the size-tunable confinement energy characteristic of GeSn nanoalloys has been shown to greatly increase the energy gaps, resulting in tunable visible to near-IR optical properties. Herein, the authors summarize recent advances in the synthesis of 0D and 1D GeSn alloy nanostructures and their emerging physical properties in light of their potential applications in advanced electronic and photonic technologies.