Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2

Autor: Moshe G. Harats, Kirill I. Bolotin, Mengxiong Qiao, Jan N. Kirchhof, Kyrylo Greben
Rok vydání: 2020
Předmět:
Materials science
Photoluminescence
Exciton
photonics
FOS: Physical sciences
02 engineering and technology
Condensed Matter - Soft Condensed Matter
condensed-matter physics
Molecular physics
01 natural sciences
Spectral line
photonic devices
010309 optics
chemistry.chemical_compound
Condensed Matter::Materials Science
Optical imaging
Optical materials
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
0103 physical sciences
Monolayer
Condensed Matter::Quantum Gases
Physics
Valence (chemistry)
Condensed Matter - Mesoscale and Nanoscale Physics
Condensed matter physics
Atomic force microscopy
Condensed Matter::Other
business.industry
Dynamics (mechanics)
Energy conversion efficiency
Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
021001 nanoscience & nanotechnology
optics
Atomic and Molecular Physics
and Optics
3. Good health
Electronic
Optical and Magnetic Materials
Semiconductor
Silicon nitride
chemistry
Excited state
Soft Condensed Matter (cond-mat.soft)
Condensed Matter::Strongly Correlated Electrons
Photonics
0210 nano-technology
business
Zdroj: Nature Photonics
ISSN: 1749-4893
1749-4885
Popis: We investigate the transport of excitons and trions in monolayer semiconductor WS$_2$ subjected to controlled non-uniform mechanical strain. We actively control and tune the strain profiles with an AFM-based setup in which the monolayer is indented by an AFM tip. Optical spectroscopy is used to reveal the dynamics of the excited carriers. The non-uniform strain configuration locally changes the valence and conduction bands of WS$_2$, giving rise to effective forces attracting excitons and trions towards the point of maximum strain underneath the AFM tip. We observe large changes in the photoluminescence spectra of WS$_2$ under strain, which we interpret using a drift-diffusion model. We show that the transport of neutral excitons, a process that was previously thought to be efficient in non-uniformly strained 2D semiconductors and termed as "funneling", is negligible at room temperature in contrast to previous observations. Conversely, we discover that redistribution of free carriers under non-uniform strain profiles leads to highly efficient conversion of excitons to trions. Conversion efficiency reaches $\simeq 100\%$ even without electrical gating. Our results explain inconsistencies in previous experiments and pave the way towards new types of optoelectronic devices.
6 pages, 4 figures
Databáze: OpenAIRE
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