Mr. Junhong Yu Profile

Junhong Yu

at Nanyang Technological Univ

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Proceedings Article | 8 March 2019 Presentation

Modulating trion population to control light amplification in a colloidal quantum-dot device (Conference Presentation)

Junhong Yu, Cuong Dang

Proceedings Volume 10912, 109120A (2019) https://doi.org/10.1117/12.2509305

KEYWORDS: Quantum dots, Modulation, Control systems, Quantum efficiency, Continuous wave operation, Dielectrics, Electrons, Excitons, Laser applications

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As an optical gain medium, colloidal quantum dots (CQDs) are suffering from band-edge state degeneracy which demands multiple-exciton to achieve population inversion. However, fast non-radiative Auger recombination in the multiple-exciton CQDs increases the lasing threshold and limits the gain lifetime. Here, by embedding the quasi type-II CQDs (CdSe/CdS/ZnS core/shell/shell) into the Sawyer−Tower circuit to apply a potential that is experienced as an electric field by the CQDs, we have reached and showed tunable amplified spontaneous emission (ASE) threshold in a long-sought practical device where the CQDs sandwiched between two dielectric layers to retain their high quantum efficiency as in parent solution (quantum yield of > 70%). Singly-charged CQDs help building up population inversion due to pre-existing electrons while strongly enhanced Auger recombination in multiple-charged CQDs stymies the optical amplification. The approach allows us to fine-tune and achieve the optimal charging level to utilize the advantages of singly charged CQDs and avoid the adverse effect of doubly charged CQDs. In addition to experimentally demonstrating threshold tunability, we also developed a kinetic equation model to systematically analyze the electric field dependent ASE threshold. The kinetic model not only confirms our experimental results but also presents to be a reliable tool for accessing the requirements of charging level to achieve nearly zero-threshold trion gain in CQDs. The implications, then, to potential applications of our robust and environment-undependable tuning method are broad, from controlling exciton recombination dynamics to continuous wave (CW) or possibly electrically pumped CQD lasers.

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