Energy Gap Tuning and Carrier Dynamics in Colloidal Ge1–x Sn x Quantum Dots

• Published in: The journal of physical chemistry letters 2016-09, Vol.7 (17), p.3295-3301
• Main Authors: Hafiz, Shopan A, Esteves, Richard J Alan, Demchenko, Denis O, Arachchige, Indika U, Özgür, Ümit
• Format: Article
• Language: English
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.6b01333

Optical transition energies and carrier dynamics in colloidally synthesized 2.0 ± 0.8 nm Ge1–x Sn x quantum dots (x = 0.055–0.236) having visible luminescence were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopy supported by first-principles calculations. By changing Sn content from x = 0.055 to 0.236, experimentally determined HOMO–LUMO gap at 15 K was tuned from 1.88 to 1.61 eV. Considering the size and compositional variations, these values were consistent with theoretically calculated ones. At 15 K, time-resolved PL revealed slow decay of luminescence (3–27 μs), likely due to the recombination of spin-forbidden dark excitons and recombination of carriers trapped at surface states. Increasing Sn concentration to 23.6% led to 1 order of magnitude faster recombination. At 295 K, PL decays were 3 orders of magnitude faster (9–28 ns) owing to the thermal activation of bright excitons and carrier detrapping from surface states.