Continuous-wave infrared optical gain and amplified spontaneous emission at ultralow threshold by colloidal HgTe quantum dots
Pieter Geiregat (Universiteit Gent)
A.J. Houtepen (Universiteit Gent, TU Delft - ChemE/Opto-electronic Materials)
Laxmi Kishore Sagar (Universiteit Gent)
Ivan Infante (Vrije Universiteit Amsterdam)
Felipe Zapata (Vrije Universiteit Amsterdam)
Valeriia Grigel (Universiteit Gent)
Guy Allan (IEMN Institut d'Electronique de Microelectronique et de Nanotechnologie)
Christophe Delerue (IEMN Institut d'Electronique de Microelectronique et de Nanotechnologie)
D. Van Thourhout (Universiteit Gent)
Z. Hens (Universiteit Gent)
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Abstract
Colloidal quantum dots (QDs) raise more and more interest as solution-processable and tunable optical gain materials. However, especially for infrared active QDs, optical gain remains inefficient. Since stimulated emission involves multifold degenerate band-edge states, population inversion can be attained only at high pump power and must compete with efficient multi-exciton recombination. Here, we show that mercury telluride (HgTe) QDs exhibit size-tunable stimulated emission throughout the near-infrared telecom window at thresholds unmatched by any QD studied before. We attribute this unique behaviour to surface-localized states in the bandgap that turn HgTe QDs into 4-level systems. The resulting long-lived population inversion induces amplified spontaneous emission under continuous-wave optical pumping at power levels compatible with solar irradiation and direct current electrical pumping. These results introduce an alternative approach for low-threshold QD-based gain media based on intentional trap states that paves the way for solution-processed infrared QD lasers and amplifiers.