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Photoluminescence Studies of Excitonic Complexes in Atomically Thin Mo(S_ySe_{1-y})₂ Alloys

100%
Jadczak J.
Acta Physica Polonica A
|
2017
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vol. 132
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issue 2
307-312
EN
Transition metal dichalcogenides show new emergent properties at monolayer thickness, notably strong Coulomb and electron-phonon interactions enable new insight into physics of many body effects. Here, we report photoluminescence and reflectivity contrast measurements of excitons (X) and trions (T) and the Raman spectra of phonons in monolayers of Mo(S_ySe_{1-y})₂ alloys with sulfur mole content from y=0 up to y=1. Binary MoSe₂ and ternary Mo(S_ySe_{2-y}) alloys exhibit contrasting behavior in the temperature evolution of excitons and trions photoluminescence intensity from T=7-295 K. In MoSe₂ a trion dominates photoluminescence spectra at low temperatures but exciton dominates photoluminescence at higher temperature. In contrast, in ternary Mo(S_ySe_{1-y})₂ alloys and MoS₂ trions dominate photoluminescence spectra at all measured temperatures, with the trion to exciton photoluminescence intensity ratio increasing with sulfur content. We attribute the strong increase of the trion photoluminescence intensity in Mo(S_ySe_{1-y})₂ monolayers with increase of sulfur mole content to the significant increase of the two-dimensional electron gas concentration and also to the strong exciton-trion coupling mediated by an optical phonon. We also demonstrate that increasing sulfur content in Mo(S_ySe_{1-y})₂ alloys stabilizes total photoluminescence intensity at high temperature.
2
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Combined Exciton-Cyclotron Resonance in Photoluminescence of a Two-Dimensional Hole Gas

39%
Jadczak J., Bryja L., Płochocka P., Wójs A., Misiewicz J., Maude D., Potemski M.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
852-853
EN
A two-dimensional hole gas in an asymmetric GaAs/Ga_{1-x}Al_{x}As quantum well is studied by polarization-resolved photoluminescence in high magnetic fields (up to B = 20 T) and at low temperatures (down to T = 50 mK). In addition to the previously reported dominant emission channels of various free and acceptor-bound trions, the high-energy hole cyclotron replicas of the bound states are now also observed, corresponding to the combined exciton-cyclotron resonance. Identification of different transitions in the rich, multi-peak spectra was possible by the analysis of optical selection rules and comparison of the experimental spectra with realistic numerical calculations.
3
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Nonlinear Zeeman Splitting of Holes in Doped GaAs Heterostructures

39%
Kubisa M., Ryczko K., Jadczak J., Bryja L., Misiewicz J., Potemski M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
609-611
EN
Polarization-resolved photoluminescence from two-dimensional GaAs/GaAlAs heterostructures doped with acceptors was studied in high magnetic fields. Measurements were carried out in low temperatures up to 2 K and magnetic field up to 21 T. Experiments performed in the Faraday configuration enabled to resolve hole states with different spin orientation. We observed a nonlinear behavior of valence-band g factor in strong magnetic fields. To explain obtained results, a detailed theoretical calculation was carried out based on the Luttinger model for valence-band states. We examined the spin splitting of hole levels under the influence of both external magnetic field and built-in electric field existing in doped heterostructures. Changes of hole g factor with the width of the structure and the density of two-dimensional carriers are discussed.
4
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Evidence of Singlet-Triplet Crossing in Photoluminescence of Positively Charged Excitons in GaAs Quantum Wells

33%
Bryja L., Wójs A., Jadczak J., Misiewicz J., Płochocka P., Potemski M., Reuter D., Wieck A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1073-1077
EN
Positively charged excitons in a two-dimensional hole gas in symmetric and asymmetric GaAs/Ga_{1-x}Al_{x}As quantum wells are studied in polarization-resolved photoluminescence experiments in high magnetic fields B (up to 23 T) and low temperatures (down to 300 mK). The experiments are accompanied by numerical calculations of a real structure. The whole family of trions (the singlet and a pair of triplets) are observed. The Coulomb energies crossing of singlet and triplet is found: hidden in symmetric and visible in asymmetric structures.
5
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Exciton Exchange between Nearly-Free and Acceptor-Bound States of a Positive Trion Assisted by Cyclotron Excitation

33%
Jadczak J., Bryja L., Wójs A., Bartsch G., Yakovlev D., Bayer M., Plochocka P., Potemski M., Reuter D., Wieck A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
600-601
EN
In magneto-photoluminescence spectra of a two-dimensional hole gas in a GaAs quantum well we observe coupling of two different radiative states. The pair of coupled states are an acceptor-bound trion AX^{+} and an essentially free (only weakly localized by a shallow lateral potential) trion X^{+}, brought into resonance by an additional cyclotron excitation controlled by the magnetic field. The coupling mechanism is the exciton transfer, and the optical signature is a clear anticrossing of the emission lines of an X^{+} and a cyclotron replica of the AX^{+}.
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