Quantum Shells Boost the Optical Gain of Lasing Media
James Cassidy, Benjamin T. Diroll, Navendu Mondal, David B. Berkinsky, Kehui Zhao, Dulanjan Harankahage, Dmitry Porotnikov, Reagan Gately, Dmitriy Khon, Andrew H. Proppe, Moungi G. Bawendi, Richard D. Schaller, Anton V. Malko, Mikhail Zamkov
Abstract
Auger decay of multiple excitons represents a significant obstacle to photonic applications of semiconductor quantum dots (QDs). This nonradiative process is particularly detrimental to the performance of QD-based electroluminescent and lasing devices. Here, we demonstrate that semiconductor quantum shells with an "inverted" QD geometry inhibit Auger recombination, allowing substantial improvements to their multiexciton characteristics. By promoting a spatial separation between multiple excitons, the quantum shell geometry leads to ultralong biexciton lifetimes (>10 ns) and a large biexciton quantum yield. Furthermore, the architecture of quantum shells induces an exciton-exciton repulsion, which splits exciton and biexciton optical transitions, giving rise to an Auger-inactive single-exciton gain mode. In this regime, quantum shells exhibit the longest optical gain lifetime reported for colloidal QDs to date (>6 ns), which makes this geometry an attractive candidate for the development of optically and electrically pumped gain media.