Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots.
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Results from the PLE spectroscopy at low temperature and under a high magnetic field (up to 14 T) were compared.Our findings show that the profile of the PLE resonances associated with the bound transitions disintegrated and broadened.The degree of spectral linewidth broadening was larger for the excited state in smaller QDs because of the higher crossed joint density of states and scattering rate.
Affiliation: Institute of Nanoscience, National Chung Hsing University, 250 Kuo Kuang Rd,, Taichung 402, Taiwan. ysuen@phys.nchu.edu.tw.
ABSTRACT
In this report, the influence of the intrinsic transitions between bound-to-delocalized states (crossed states or quasicontinuous density of electron-hole states) on photoluminescence excitation (PLE) spectra of InAs quantum dots (QDs) was investigated. The InAs QDs were different in size, shape, and number of bound states. Results from the PLE spectroscopy at low temperature and under a high magnetic field (up to 14 T) were compared. Our findings show that the profile of the PLE resonances associated with the bound transitions disintegrated and broadened. This was attributed to the coupling of the localized QD excited states to the crossed states and scattering of longitudinal acoustical (LA) phonons. The degree of spectral linewidth broadening was larger for the excited state in smaller QDs because of the higher crossed joint density of states and scattering rate. No MeSH data available. |
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Mentions: To verify the resonances in the PLE signals, which are signatures from the QD excited-states transitions, PLE measurements under a magnetic field were performed. Figure 9 shows the magnetic field dependent PLE spectra of the larger QD sample with magnetic field scanned from 0 to 14 T. Splitting and a blue shift in energy were observed with increasing magnetic field for the two resonances at 158 and 222 meV, respectively. Under a magnetic field, the energy levels in 0D quantum structures can be modified by the effects of the diamagnetic shift or Zeeman splitting. The energy level modification due to the diamagnetic shift is relative small (approximately 1 to 2 meV) even at a magnetic field intensity of 14 T. The amount of energy splitting due to Zeeman effect, ΔEZeeman, is given by the following equation: , where mℓ is the angular quantum number of the 0D quantum structures, e is the electron charge, ħ is the Planck's constant, and B is the magnetic field. For excited state carrying angular momentum mℓ of ± 1 (p-like state), the amount of energy splitting can be expressed as . By placing an effective mass of 0.05 m0 (for the InAs/GaAs quantum structures) into the above equation, a splitting in energy of about 32.39 meV was obtained for the p-like excited state transition. This number is quite close to the energy splitting (approximately 33 meV) of the resonance measured at 158 meV in our PLE spectrum. For the s-like transition, only the diamagnetic shift of approximately 1 meV is shown because mℓ = 0. Therefore, the two peaks that appeared at 158 and 222 meV in the PLE spectra resulted from the transitions of p-like and s-like excited states, respectively. |
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Affiliation: Institute of Nanoscience, National Chung Hsing University, 250 Kuo Kuang Rd,, Taichung 402, Taiwan. ysuen@phys.nchu.edu.tw.
No MeSH data available.