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S. I. Pokutnyi
spectrum of this exciton depends on QD size [5]. Due to low electron and hole wave
function overlap, an SIE shows the long lifetime [1, 2].
The use of nanosystems based on semiconductor and dielectric QDs as the active
regions of nanolasers is hindered by a small binding energy of exciton E ex (a) (where
a is the QD radius) in these nanosystems [6]. In this context, investigations aimed
at finding nanostructures with significantly increased E ex (a) values are of considerable importance. The effect of a significant increase in the SIE binding energy (by
almost two orders of magnitude) is found in nanosystems containing semiconductor
(zinc selenide, germanium) and dielectric (aluminum oxide) QD, compared with the
exciton binding energy in the corresponding single crystals [4–12]. Such an effect
of the significant increase in the SIE binding energy opens the possibility for the use
of nanosystems as an active field of nanolasers operating on exciton transitions at
room temperatures.
The most promising applications for fiber-optic communication lines were Ge/Si
heterostructures with germanium QDs, on the basis of which light-emitting diodes
have already been fabricated that emit at room temperature in the near-infrared (200–
960) meV wavelength range [13–17]. It was shown that interband and intraband
transitions between SIE states caused significant emission in the infrared region of
wavelengths in the energy range (≤330 meV) in the studied Ge/Si heterostructure
with germanium QDs [5]. Moreover, this energy range (≤330 meV) was contained
in the spectral region (200–960) meV, which was observed in experiments [13–17].
Such Ge/Si nanostructures with germanium QDs were promising for the creation of
new elements of nanoelectronics in terms of realizing effective radiation sources of
the visible and infrared ranges, and can also be used for new optoelectronic devices
(in optical modulators, in optical switches, in filters, and converters) [18, 19].
An important role in exciton physics is played by SIE. A high lifetime makes it
possible to use SIE in a wide area from Bose gas creation [20, 21] to instrumentation as for the development of excitonic devices with energy-efficient computation
and seamless coupling to optical communication [22]. These devices include traps,
lattices, conveyers, and ramps, which are used for studying basic properties of cold
SIE, as well as excitonic transistors, routers, and photon storage devices, which hold
the potential for creating excitonic signal processing devices and excitonic circuits
[22].
However, the temperature range for exciton existence was limited by low temperatures for a long time, due to low its binding energy. Recently, the authors of [23,
24] have found the SIEs with high binding energy in van der Waals heterostructures.
This gives the opportunity to study high-temperature quantum Bose gases and to
create excitonic devices operating at room temperature [25–27].
In [1–5], it is shown that the formation of SIE can make a significant contribution
to the optical absorption spectra in the visible and near-infrared regions and blur the
absorption edge. The mentioned above mechanisms of absorption spectra formation
and low-threshold optical nonlinearity are effective under the condition of large
oscillator strength and large SIE electric dipole moment of transition between SIE
states.
S. I. Pokutnyi
spectrum of this exciton depends on QD size [5]. Due to low electron and hole wave
function overlap, an SIE shows the long lifetime [1, 2].
The use of nanosystems based on semiconductor and dielectric QDs as the active
regions of nanolasers is hindered by a small binding energy of exciton E ex (a) (where
a is the QD radius) in these nanosystems [6]. In this context, investigations aimed
at finding nanostructures with significantly increased E ex (a) values are of considerable importance. The effect of a significant increase in the SIE binding energy (by
almost two orders of magnitude) is found in nanosystems containing semiconductor
(zinc selenide, germanium) and dielectric (aluminum oxide) QD, compared with the
exciton binding energy in the corresponding single crystals [4–12]. Such an effect
of the significant increase in the SIE binding energy opens the possibility for the use
of nanosystems as an active field of nanolasers operating on exciton transitions at
room temperatures.
The most promising applications for fiber-optic communication lines were Ge/Si
heterostructures with germanium QDs, on the basis of which light-emitting diodes
have already been fabricated that emit at room temperature in the near-infrared (200–
960) meV wavelength range [13–17]. It was shown that interband and intraband
transitions between SIE states caused significant emission in the infrared region of
wavelengths in the energy range (≤330 meV) in the studied Ge/Si heterostructure
with germanium QDs [5]. Moreover, this energy range (≤330 meV) was contained
in the spectral region (200–960) meV, which was observed in experiments [13–17].
Such Ge/Si nanostructures with germanium QDs were promising for the creation of
new elements of nanoelectronics in terms of realizing effective radiation sources of
the visible and infrared ranges, and can also be used for new optoelectronic devices
(in optical modulators, in optical switches, in filters, and converters) [18, 19].
An important role in exciton physics is played by SIE. A high lifetime makes it
possible to use SIE in a wide area from Bose gas creation [20, 21] to instrumentation as for the development of excitonic devices with energy-efficient computation
and seamless coupling to optical communication [22]. These devices include traps,
lattices, conveyers, and ramps, which are used for studying basic properties of cold
SIE, as well as excitonic transistors, routers, and photon storage devices, which hold
the potential for creating excitonic signal processing devices and excitonic circuits
[22].
However, the temperature range for exciton existence was limited by low temperatures for a long time, due to low its binding energy. Recently, the authors of [23,
24] have found the SIEs with high binding energy in van der Waals heterostructures.
This gives the opportunity to study high-temperature quantum Bose gases and to
create excitonic devices operating at room temperature [25–27].
In [1–5], it is shown that the formation of SIE can make a significant contribution
to the optical absorption spectra in the visible and near-infrared regions and blur the
absorption edge. The mentioned above mechanisms of absorption spectra formation
and low-threshold optical nonlinearity are effective under the condition of large
oscillator strength and large SIE electric dipole moment of transition between SIE
states.