Abstract
Semiconductors that can provide optical gain at extremely low carrier density levels are critically important for applications such as energy efficient nanolasers. However, all current semiconductor lasers are based on traditional semiconductor materials that require extremely high density levels above the so-called Mott transition to realize optical gain. The new emerging 2D materials provide unprecedented opportunities for studying new excitonic physics and exploring new optical gain mechanisms at much lower density levels due to the strong Coulomb interaction and co-existence and mutual conversion of excitonic complexes. Here, we report a new gain mechanism involving charged excitons or trions in electrically gated 2D molybdenum ditelluride well below the Mott density. Our combined experimental and modelling study not only reveals the complex interplay of excitonic complexes well below the Mott transition but also establishes 2D materials as a new class of gain materials at densities 4–5 orders of magnitude lower than those of conventional semiconductors and provides a foundation for lasing at ultralow injection levels for future energy efficient photonic devices. Additionally, our study could help reconcile recent conflicting results on 2D materials: While 2D material-based lasers have been demonstrated at extremely low densities with spectral features dominated by various excitonic complexes, optical gain was only observed in experiments at densities several orders of magnitude higher, beyond the Mott density. We believe that our results could lead to more systematic studies on the relationship between the mutual conversion of excitonic species and the existence of optical gain well below the Mott transition.
Highlights
Dynamical processes of quasiparticles, such as excitons and their various associated complexes, in solids are at the core of fundamental condensed matter physics
Our intention was to probe the inner mechanisms of the co-existence of or transition kinetics among various excitonic complexes as the pumping increased and to investigate the possibility, origin, and physical mechanism of optical gain in such low-density regimes
In summary, we have conducted systematic PL and reflectance spectroscopy experiments on electrically gated MoTe2 devices to investigate possible optical gain at low excitation levels. Our results on both monolayer and bilayer samples show the clear existence of optical gain at such low carrier density levels, orders of magnitude below the Mott density (MD)
Summary
Dynamical processes of quasiparticles, such as excitons and their various associated complexes (including charged excitons or trions, biexcitons, and other highly correlated objects1), in solids are at the core of fundamental condensed matter physics. Limited study of the stimulated emission through excitonic complexes in the intermediate density regime has produced both scientific discoveries and technological breakthroughs in semiconductor photonics research, such as optical gain based on excitons[8,9], biexcitons[10,11], trions[12,13], and polariton scattering[14] in III–V or II–VI compound semiconductors or the multiexciton[15] and single-exciton[16] gain observed in nanocrystals These relatively rare gain mechanisms have resulted in lasing demonstrations at much lower pumping thresholds than conventional lasers, which require higher pumping above the MD
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
