Strain tuning of the Stokes shift in atomically thin semiconductors

Nanoscale ◽  
2020 ◽  
Vol 12 (40) ◽  
pp. 20786-20796
Author(s):  
Iris Niehues ◽  
Philipp Marauhn ◽  
Thorsten Deilmann ◽  
Daniel Wigger ◽  
Robert Schmidt ◽  
...  
Keyword(s):  
Mechanical Strain ◽  
Stokes Shift ◽  
2D Semiconductors ◽  
Excitonic Transitions

We measure the Stokes shift of excitonic transitions in 2D semiconductors and tune it by mechanical strain.

Origin of the Stokes Shift: A Geometrical Model of Exciton Spectra in 2D Semiconductors

1994 ◽  
Vol 72 (12) ◽  
pp. 1945-1945 ◽  
Author(s):  
Fang Yang ◽  
M. Wilkinson ◽  
E. J. Austin ◽  
K. P. O'Donnell
Keyword(s):  
Stokes Shift ◽  
Geometrical Model ◽  
2D Semiconductors

Origin of the Stokes shift: A geometrical model of exciton spectra in 2D semiconductors

1993 ◽  
Vol 70 (3) ◽  
pp. 323-326 ◽  
Author(s):  
Fang Yang ◽  
M. Wilkinson ◽  
E. J. Austin ◽  
K. P. O’Donnell
Keyword(s):  
Stokes Shift ◽  
Geometrical Model ◽  
2D Semiconductors

scholarly journals Modulation of photocarrier relaxation dynamics in two-dimensional semiconductors

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Yuhan Wang ◽  
Zhonghui Nie ◽  
Fengqiu Wang
Keyword(s):  
Electric Fields ◽  
Mechanical Strain ◽  
Transition Metal Dichalcogenides ◽  
Binding Energies ◽  
Two Dimensional ◽  
Coulomb Interactions ◽  
Relaxation Dynamics ◽  
Strong Light ◽  
2D Semiconductors ◽  
Metal Dichalcogenides

AbstractDue to strong Coulomb interactions, two-dimensional (2D) semiconductors can support excitons with large binding energies and complex many-particle states. Their strong light-matter coupling and emerging excitonic phenomena make them potential candidates for next-generation optoelectronic and valleytronic devices. The relaxation dynamics of optically excited states are a key ingredient of excitonic physics and directly impact the quantum efficiency and operating bandwidth of most photonic devices. Here, we summarize recent efforts in probing and modulating the photocarrier relaxation dynamics in 2D semiconductors. We classify these results according to the relaxation pathways or mechanisms they are associated with. The approaches discussed include both tailoring sample properties, such as the defect distribution and band structure, and applying external stimuli such as electric fields and mechanical strain. Particular emphasis is placed on discussing how the unique features of 2D semiconductors, including enhanced Coulomb interactions, sensitivity to the surrounding environment, flexible van der Waals (vdW) heterostructure construction, and non-degenerate valley/spin index of 2D transition metal dichalcogenides (TMDs), manifest themselves during photocarrier relaxation and how they can be manipulated. The extensive physical mechanisms that can be used to modulate photocarrier relaxation dynamics are instrumental for understanding and utilizing excitonic states in 2D semiconductors.

A snapshot review on exciton engineering in deformed 2D materials

MRS Advances ◽  
2020 ◽  
Vol 5 (64) ◽  
pp. 3491-3506
Author(s):  
Juyoung Leem
Keyword(s):  
Strain Gradient ◽  
2D Materials ◽  
Mechanical Strain ◽  
Bandgap Energy ◽  
Mechanical Stimuli ◽  
2D Material ◽  
2D Semiconductors ◽  
Energy Gradient ◽  
Excitonic Effects ◽  
External Stimuli

AbstractMost optoelectronic characteristics of two-dimensional (2D) materials are associated with excitonic effects. Excitonic effects in 2D material have been intensively investigated, and various efforts to engineer exciton behavior in 2D materials have been reported for advanced nanophotonic and optoelectronic applications. Excitons in 2D semiconductors can be controlled by external stimuli, including mechanical, electrical, thermal, and magnetic stimuli. Mechanical stimuli applied to a 2D material can generate uniform or non-uniform deformation and strain gradient in the 2D lattice, which creates a strain-induced bandgap energy gradient in the 2D material. In an inhomogeneous bandgap energy gradient generated by a non-uniform strain gradient, excitons drift across the energy gradient. Exciton engineering in deformed 2D materials aims to control exciton movement by mechanical strain. In this snapshot review, we focus on exciton engineering in a mechanically deformed 2D material and their potential towards advanced optoelectronic and photonic applications.

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

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