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Analysis of Optical Properties of MoS₂ Monolayer using Minimal-Basis Tight-Binding Models

100%
Nouri N., Potasz P., Zia Borujeni S., Wójs A., Rashedi G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
313-315
EN
Optical properties of transition metal dichalcogenides monolayer of MoS₂ are analyzed using multi-orbital tight-binding models with only Mo d-orbitals (three-band model) and with an inclusion of S p-orbitals (six-band model). We look at band structures, momentum matrix elements between valence and conduction band, and joint optical density of states. Good agreement between the two models is shown in a vicinity of K point of the Brillouin zone. On line connecting K and Γp points, a local conduction band minimum at Q point is recovered only by six-band model in agreement with density functional theory and experimental results. We show that optical transitions at this point are active for both light polarizations. A peak in joint optical density of states is also seen at this point suggesting its potentially important role in a proper description of excitonic effects.
2
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Coupling of Quantum Dots with Quantum Wells in a System Based on (Cd,Zn,Mg)Te

84%
Połczyńska K., Janik E., Kossacki P., Pacuski W.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
369-371
EN
Coupled low dimensional structures have potential applications in quantum computing and spintronics. Using molecular beam epitaxy we fabricated three kinds of systems of coupled quantum wells and quantum dots with different energy order: wells at higher energy than dots, resonant structures, and dots at higher energy than wells. By analysis of photoluminescence and reflectivity spectra, we conclude that there is a possibility of effective carrier tunneling between structures, which opens possibility of subsequent testing of spin transfer efficiency.
3
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Optimizing the InGaAs/GaAs Quantum Dots for 1.3 μm Emission

84%
Maryński A., Mrowiński P., Ryczko K., Podemski P., Gawarecki K., Musiał A., Misiewicz J., Quandt D., Strittmatter A., Rodt S., Reitzenstein S., Sęk G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
386-390
EN
Hereby we present comprehensive experimental and theoretical study on fundamental optical properties and electronic structure of GaAs-based quantum dots grown using metalorganic chemical vapor deposition technique. The substantial redshift of emission, to the second telecommunication window of 1.3 μm, in comparison to standard InGaAs/GaAs quantum dots is obtained via strain engineering utilizing additional capping layer of In_{0.2}Ga_{0.8}As in this context referred to as strain reducing layer. It ensures lowering of the energy of the ground state transition to more application relevant spectral range. Optical properties of the quantum dot structure has been experimentally characterized by means of photoreflectance spectroscopy and power-dependent photoluminescence revealing 3 transitions originating from hybrid states confined in an asymmetric double quantum well formed of the wetting layer and strain reducing layer, as well as higher states of the quantum dots themselves with the first excited state transition separated by 67 meV from the ground state transition. Origin of the observed transitions was confirmed in theoretical modelling using 1-band single-particle approach for the quantum well part, and excitonic quantum dot spectrum obtained within 8 band k·p formalism followed by configuration interaction calculations, respectively. Additionally, photoluminescence excitation spectroscopy measurements allowed to identify a spectral range for efficient quasi-resonant excitation of the investigated quantum dots into the 2D density of states to be in the range of 835-905 nm.
4
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Valence intersubband gain without population inversion

84%
Pereira M.
Open Physics
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2010
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vol. 8
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issue 1
61-64
EN
Terahertz gain without population inversion is studied in thin III–V semiconductor quantum wells. Nonequilibrium hole populations leading to intervalence gain in the transverse electric mode are investigated. The results are obtained with a Keldysh Nonequilibrium Green’s Functions approach that takes into account bandstructure, manybody and nonequilibrium effects.
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