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Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots.

Shih CI, Lin CH, Lin SC, Lin TC, Sun KW, Voskoboynikov OA, Lee CP, Suen YW - Nanoscale Res Lett (2011)

Bottom Line: 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.

View Article: PubMed Central - HTML - PubMed

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.


Normalized PLE spectra with the PLE signal at 1.42 eV at 1.4 K.
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Figure 11: Normalized PLE spectra with the PLE signal at 1.42 eV at 1.4 K.

Mentions: To interpret our experimental findings, bound-to-bound transitions and the bound-to-delocalized state transitions were calculated as a function of dot size at constant confinement potentials. A self-consistent iterative approach was used to calculate the energy levels of electrons and holes using non-parabolic and parabolic approximation for the conduction and valence bands, respectively. The calculations were done for a single dot in a large numerical box. The simulated dot geometries were determined from AFM measurements of our QD samples. The calculated onset energies of the continuum measured from the WL edge were 106 and 211 meV for QD1 and QD2, respectively, and are indicated with blue arrows, shown in Figure 10. Meanwhile, to compare different values of acoustic phonon broadening efficiencies α for QD1 and QD2, the QD-independent values of the PLE background signal needs to be determined. This was achieved by normalizing the PLE spectra with the WL absorption edge [12] at 1.42 eV for both QD1 and QD2, as shown in Figures 11a, b. However, the excited state of QD1 has the highest value in the normalized PLE intensity even though the energies of the excited states of both QD samples were above the onset energies of the continuum. Therefore, the excited state of QD1 had a higher acoustic phonon broadening efficiency and suffered more from the LA phonon-assisted scattering effect, which led to a much larger degree of linewidth broadening. Notably, the excited state of the QD2 at the higher energy also has a larger normalized PLE intensity than the excited state at the lower energy, which showed a broader spectral profile due to the higher phonon scattering rate.


Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots.

Shih CI, Lin CH, Lin SC, Lin TC, Sun KW, Voskoboynikov OA, Lee CP, Suen YW - Nanoscale Res Lett (2011)

Normalized PLE spectra with the PLE signal at 1.42 eV at 1.4 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211504&req=5

Figure 11: Normalized PLE spectra with the PLE signal at 1.42 eV at 1.4 K.
Mentions: To interpret our experimental findings, bound-to-bound transitions and the bound-to-delocalized state transitions were calculated as a function of dot size at constant confinement potentials. A self-consistent iterative approach was used to calculate the energy levels of electrons and holes using non-parabolic and parabolic approximation for the conduction and valence bands, respectively. The calculations were done for a single dot in a large numerical box. The simulated dot geometries were determined from AFM measurements of our QD samples. The calculated onset energies of the continuum measured from the WL edge were 106 and 211 meV for QD1 and QD2, respectively, and are indicated with blue arrows, shown in Figure 10. Meanwhile, to compare different values of acoustic phonon broadening efficiencies α for QD1 and QD2, the QD-independent values of the PLE background signal needs to be determined. This was achieved by normalizing the PLE spectra with the WL absorption edge [12] at 1.42 eV for both QD1 and QD2, as shown in Figures 11a, b. However, the excited state of QD1 has the highest value in the normalized PLE intensity even though the energies of the excited states of both QD samples were above the onset energies of the continuum. Therefore, the excited state of QD1 had a higher acoustic phonon broadening efficiency and suffered more from the LA phonon-assisted scattering effect, which led to a much larger degree of linewidth broadening. Notably, the excited state of the QD2 at the higher energy also has a larger normalized PLE intensity than the excited state at the lower energy, which showed a broader spectral profile due to the higher phonon scattering rate.

Bottom Line: 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.

View Article: PubMed Central - HTML - PubMed

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.