426
14 Nanostructures
Fig. 14.44 Biexciton
binding energy determined
for a single InAs/GaAs
quantum dot for various
annealing times. Data
from [1413]
Fig. 14.45 Luminescence
of charged excitons from a
single quantum ring at
T = 4.2 K versus the bias
voltage with which the
number of electrons in the
quantum dot N is tuned
from zero to N > 3.
Adapted from [1415],
reprinted with permission,
©2000, Springer Nature
excitons depends (due to the Coulomb interaction) on the number of the electrons present (Fig. 14.45).
The singly negatively charged exciton X
− is also called a trion.
The interaction of a spin with an exciton in a CdTe quantum dot has been observed in [1416]. If
the CdTe quantum dot is pure, a single line arises. If the dot contains a single Mn atom, the exchange
interaction of the exciton with the Mn S = 5/2 spin leads to a six-fold splitting of the exciton line
(Fig. 14.46. In an external magnetic field a splitting into a total of twelve lines due to Zeeman effect at
the Mn spin is observed.
In a QD ensemble, optical transitions are inhomogeneously broadened due to fluctuations in the QD
size and the size dependence of the confinement energies (Fig. 14.47). Interband transitions involving
electrons and holes suffer from the variation of the electron and hole energies:
σ E ∝
∂ E e
∂ L
+
∂ E h
∂ L
δL .
(14.24)
A typical relative size inhomogeneity of σ L /L of 7% leads to several tens of meV broadening. Additional to broadening due to different sizes fluctuations of the quantum dot shape can also play a role.
The confinement effect leads to an increase of the recombination energy with decreasing quantumdot size. This effect is nicely demonstrated with colloidal quantum dots of different size as shown in
Fig. 14.48.
14 Nanostructures
Fig. 14.44 Biexciton
binding energy determined
for a single InAs/GaAs
quantum dot for various
annealing times. Data
from [1413]
Fig. 14.45 Luminescence
of charged excitons from a
single quantum ring at
T = 4.2 K versus the bias
voltage with which the
number of electrons in the
quantum dot N is tuned
from zero to N > 3.
Adapted from [1415],
reprinted with permission,
©2000, Springer Nature
excitons depends (due to the Coulomb interaction) on the number of the electrons present (Fig. 14.45).
The singly negatively charged exciton X
− is also called a trion.
The interaction of a spin with an exciton in a CdTe quantum dot has been observed in [1416]. If
the CdTe quantum dot is pure, a single line arises. If the dot contains a single Mn atom, the exchange
interaction of the exciton with the Mn S = 5/2 spin leads to a six-fold splitting of the exciton line
(Fig. 14.46. In an external magnetic field a splitting into a total of twelve lines due to Zeeman effect at
the Mn spin is observed.
In a QD ensemble, optical transitions are inhomogeneously broadened due to fluctuations in the QD
size and the size dependence of the confinement energies (Fig. 14.47). Interband transitions involving
electrons and holes suffer from the variation of the electron and hole energies:
σ E ∝
∂ E e
∂ L
+
∂ E h
∂ L
δL .
(14.24)
A typical relative size inhomogeneity of σ L /L of 7% leads to several tens of meV broadening. Additional to broadening due to different sizes fluctuations of the quantum dot shape can also play a role.
The confinement effect leads to an increase of the recombination energy with decreasing quantumdot size. This effect is nicely demonstrated with colloidal quantum dots of different size as shown in
Fig. 14.48.