Optical Transitions and Excitonic Properties of Ge1–xSnx Alloy Quantum Dots

5 years ago

Optical Transitions and Excitonic Properties of Ge1–xSnx Alloy Quantum Dots

Ümit Özgür, Shopan Hafiz, Tanner A. Nakagawara, Denis O. Demchenko, Richard J Alan Esteves, Indika U. Arachchige, Venkatesham Tallapally

Using hybrid functional calculations and experimental characterization, we analyze optical properties of 2–3 nm Ge_1–xSn_x alloy quantum dots, synthesized by colloidal chemistry methods. Hybrid functional theory, tuned to yield experimental bulk band structure of germanium, reproduces directly measured properties of Ge_1–xSn_x quantum dots, such as lattice constants, energy gaps, and absorption spectra. Time-dependent hybrid functional calculations yield optical absorption in good agreement with experiments, and allow probing the nature of the dark excitons in quantum dots. Calculations suggest a spin-forbidden dark exciton ground state, which is supported by the changes in the photoluminescence lifetimes with temperature and tin concentrations. The synthesis and theoretical understanding of Ge_1–xSn_x alloy quantum dots will add to the overall toolbox of low to nontoxic, silicon-compatible group IV semiconductors with potential application in visible to near-infrared optoelectronics.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06458

DOI: 10.1021/acs.jpcc.7b06458