Related Experiment Video
Updated: Apr 15, 2026
15:58
Measurement of Coherence Decay in GaMnAs Using Femtosecond Four-wave Mixing
Published on: December 3, 2013
6.2K
Exciton dynamics and annihilation in WS2 2D semiconductors
1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA. libai-huang@purdue.edu.
Nanoscale
|April 1, 2015
Summary
Exciton dynamics in tungsten disulfide (WS2) 2D crystals reveal shorter lifetimes with increasing layers. Exciton-exciton annihilation is significantly faster in monolayer WS2 compared to bilayer and trilayer structures.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Spectroscopy
Background:
- Two-dimensional (2D) transition metal dichalcogenides (TMDs) like WS2 exhibit unique electronic and optical properties.
- Understanding exciton dynamics is crucial for optoelectronic applications of 2D materials.
Purpose of the Study:
- To systematically investigate exciton dynamics in monolayer, bilayer, and trilayer WS2.
- To determine exciton lifetimes and analyze exciton-exciton annihilation rates as a function of layer number.
Main Methods:
- Time-resolved photoluminescence (TRPL) spectroscopy was employed.
- Fluorescence quantum yields were measured to determine radiative and nonradiative lifetimes.
- Exciton-exciton annihilation rates were calculated using a two-particle Auger recombination model.
Main Results:
- Exciton lifetimes decrease with increasing layers: 806 ps (monolayer), 401 ps (bilayer), and 332 ps (trilayer).
- Exciton-exciton annihilation rates are significantly higher in monolayer WS2 (0.41 cm^2 s^-1) compared to bilayer (6.00 × 10^-3 cm^2 s^-1) and trilayer (1.88 × 10^-3 cm^2 s^-1).
- Exciton decay shows strong excitation density-dependence in monolayer WS2.
Conclusions:
- The layer-dependent exciton dynamics in WS2 are strongly influenced by exciton-exciton annihilation.
- Reduced many-body interactions and phonon-assisted annihilation of indirect excitons contribute to slower annihilation rates in bilayer and trilayer WS2.
More Related Videos
Related Concept Videos
01:12Fermi Level Dynamics
1.1K
The vacuum level denotes the energy threshold required for an electron to escape from a material surface. It is usually positioned above the conduction band of a semiconductor and acts as a benchmark for comparing electron energies within various materials.
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
The work...
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
The work...
1.1K
01:25Deactivation Processes: Jablonski Diagram
2.4K
Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
2.4K
01:22Carrier Generation and Recombination
1.6K
Carrier generation is the process by which electron-hole pairs (EHPs) are created within the semiconductor. In direct-bandgap semiconductors, such as gallium arsenide (GaAs), this occurs efficiently when energy absorption prompts valence electrons to leap into the conduction band, leaving behind holes.
This process is given by the generation rate G and is efficient due to the conservation of momentum between the valence band maximum and conduction band minimum.
Indirect generation involves an...
This process is given by the generation rate G and is efficient due to the conservation of momentum between the valence band maximum and conduction band minimum.
Indirect generation involves an...
1.6K
02:32The de Broglie Wavelength
34.8K
In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a table will behave like a particle; it will continue traveling in a straight line unless it collides with another ball, or it is acted on by some other force, such as friction. The ball has a well-defined position and velocity or well-defined momentum, p = mv, which is defined by mass m and velocity v at any given moment. This is the typical...
34.8K
01:01Energy Bands in Solids
2.5K
Isolated atoms have discrete energy levels that are well described by the Bohr model. And, it quantifies the energy of an electron in a hydrogen atom as En. Higher quantum numbers 'n' yield less negative, closer electron energy levels.
Band Formation:
When atoms are brought close together, as in a solid, these discrete energy levels begin to split due to the overlap of electron orbitals from adjacent atoms. This split occurs because of the Pauli exclusion principle, which states...
Band Formation:
When atoms are brought close together, as in a solid, these discrete energy levels begin to split due to the overlap of electron orbitals from adjacent atoms. This split occurs because of the Pauli exclusion principle, which states...
2.5K
02:42Valence Bond Theory
11.9K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
11.9K