1 / 21

Exciton and Biexciton Energies in GaN / AlN Quantum Dots

Exciton and Biexciton Energies in GaN / AlN Quantum Dots. G. Hönig , A. Schliwa , D. Bimberg , A. Hoffmann Teilprojekt A5. Institut für Festkörperphysik Technische Universität Berlin. gerald.hoenig@physik.tu-berlin.de. c-plane GaN / AlN QDs. Vertical electron -hole separation

terri
Download Presentation

Exciton and Biexciton Energies in GaN / AlN Quantum Dots

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ExcitonandBiexcitonEnergies in GaN/AlN Quantum Dots G. Hönig, A. Schliwa, D. Bimberg, A. Hoffmann Teilprojekt A5 Institut für Festkörperphysik Technische Universität Berlin gerald.hoenig@physik.tu-berlin.de

  2. c-plane GaN/AlN QDs • Verticalelectron-hole separation • Redshiftof X • - X energy inverse proportional to QD-height

  3. Outline Exciton States BiexcitonComplex in Relation toExciton A New Approach: Wigner-crystals

  4. Electron Hole Interaction • Direct Coulomb Interaction • relatedtocharges • attractivebetweenelectronand hole • Exchange Interaction • relatedtospins • repulsivebetweenelectronand hole • ( ifspinsare antiparallel, if parallel = 0 ) • splitsupenergiesrelatedtospinorientation direct exchange

  5. Root of 4 Exciton States Diagonalizationofthe Hamilton-matrixleadstotheeigenstates: & Imaginetheparticlestatesstemfromtheconductionand heavy hole valence band, respectively. (neglectingtheintermixed band structure) The spinswouldbe: Total spinofexcitonstates: BRIGHT: ±1 DARK: ±2 Becauseofthe repulsive natureofexchangeinteractionbetweenelectronand hole, BRIGHT stateshavealwayshigherenergythan DARK states!

  6. ExcitonandBiexciton States 3,4 opticallyactive (BRIGHT) 1,2 opticallyinactive (DARK)

  7. Experimental Findings • full linear polarization • 180° periodicity • 90° phaseshiftbetweenstates • fine-structuresplitting on the order ofmeV C. Kindel, …, Y. Arakawa, G. Hönig, …, A. Hoffmann, D. Bimberg Phys. Rev. B 81, 241309(R) (2010)

  8. Investigationsof FSS Series arecalculatedwith 20% laterallyelongated QD structures. • comparativelyhuge FSS on the order ofmeV • heightincrease (withconstantaspectratio) causesdecreaseof FSS • diameterincrease (withconstantheight) causesdecreaseof FSS • agreementwith experimental findings (blacksquares) C. Kindel, …, Y. Arakawa, G. Hönig, …, A. Hoffmann, D. Bimberg Phys. Rev. B 81, 241309(R) (2010)

  9. Outline Exciton States BiexcitonComplex in Relation toExciton A New Approach: Wigner-crystals

  10. Biexciton Relative toExciton Ebind = 2 EX - EXX

  11. MeanfieldBiexciton Biexciton Exciton Spatialelectron hole separationleadstohigherenergyofthebiexciton! CorrelationEnergy & ConditionalProbabilities

  12. Nature ofCorrelationEnergy Weak lateral hole confinement => hole canmovefreelyat QD bottom => X: Hole cancorrelateitsdensitytotheelectronposition => XX: Hole cancorrelateitsdensitytothepositionsof e, e, h => repulsive interactionsstronglydecrease, => attractiveinteractionsstronglyincrease

  13. Height Dependence Exciton Biexciton

  14. Height Dependence • Ebindincreaseswithdecreasing QD height • Exciton DARK-BRIGHT splittingisimportant • Relative to BRIGHT statesEbindcanbecomepositve

  15. Height Dependence • Ebindincreaseswithdecreasing QD height • Exciton DARK-BRIGHT splittingisimportant • Relative to BRIGHT statesEbindcanbecomepositve Slopes: Theo. = (47 ± 6) meV/eV Exp. = (51 ± 6) meV/eV D. Simeonov, …,N. Grandjean, Phys. Rev. B 77, 075306 (2008)

  16. Outline Exciton States BiexcitonComplex in Relation toExciton A New Approach: Wigner-crystals

  17. Wigner Crystal Biexciton

  18. Wigner Crystal Biexciton Coulddeclareabsenceofsplittedbiexcitonemissionlines in QD sepctrawithvisibleexcitonsplitting.

  19. Experimental Findings Is oneoftheselinesthebiexciton?

  20. Experiment vs. Wigner-XX • Avoidingholes • Attractiveexchangeinteractionbetween parallel hole spins • ≈ 25 meVenergyreductionofbiexcitonstate

  21. Summary • Groundstateexciton: 4 possiblestates • BRIGHT statessplittingofmeV • DARK statessplittingofmEV • Biexcitonandexcitonemissionlinecrossing • New sortof Wigner crystallikebiexcitonspossible • Nosplitupbiexcitonemissionlines

More Related