Polarization of Germanium Quantum
Dots in Heterostructure Ge/Si Caused
by Spatially Indirect Exciton Transitions:
Theory
Sergey I. Pokutnyi
1 Introduction
Ge/Si heterostructures with germanium quantum dots (QDs) are of the second type
of heterostructures. In them, the main electron level was located in the silicon matrix,
and the main hole level was in the germanium QD. When studying the optical properties of Ge/Si nanosystems with germanium QDs, experimental work [1] was the
first to reveal the spatial separation of electrons and holes, as a result of which electrons were localized above the QD surface, and holes moved into QDs. The transition
between such states was indirect in space. In experimental studies [1, 2], it was established that in nanosystems consisting of germanium QDs located in silicon matrices,
the excitation of spatially indirect excitons (SIE) is possible.
In [3], heterostructures, which are linear germanium QD chains on silicon
substrates, were obtained using the method of electron beam lithography. The average
radii of QD of germanium did not exceed 30 nm. In Ge/Si heterostructures with
germanium QDs, it was established in experimental works [1, 2] that low-temperature
optical absorption and photoluminescence spectra were caused by interband electron transitions from the valence band of germanium QD to the conduction band of
the silicon matrix. The photoluminescence signal of nanostructures in the infrared
spectral region (0.20–1.14) eV was observed up to room temperature [1, 2].
The theory predicts that exciton, containing a hole in QD volume and electron localized above outer spherical interface (QD—silicon matrix), has the binding
energy two orders of magnitude higher than exciton in appropriate bulk semiconductors [4, 5]. Electron and the hole are separated by centrifugal potential, as well as
polarization interaction with a curved interface (QD—silicon matrix) [5]. The energy
S. I. Pokutnyi (B)
Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 17 General
Naumov Street, Kyiv 03164, UA, Ukraine
e-mail: pokutnyi.serg@gmail.com
© Springer Nature Switzerland AG 2021
O. Fesenko and L. Yatsenko (eds.), Nanomaterials and Nanocomposites,
Nanostructure Surfaces, and Their Applications, Springer Proceedings
in Physics 246, https://doi.org/10.1007/978-3-030-51905-6_43
615
Dots in Heterostructure Ge/Si Caused
by Spatially Indirect Exciton Transitions:
Theory
Sergey I. Pokutnyi
1 Introduction
Ge/Si heterostructures with germanium quantum dots (QDs) are of the second type
of heterostructures. In them, the main electron level was located in the silicon matrix,
and the main hole level was in the germanium QD. When studying the optical properties of Ge/Si nanosystems with germanium QDs, experimental work [1] was the
first to reveal the spatial separation of electrons and holes, as a result of which electrons were localized above the QD surface, and holes moved into QDs. The transition
between such states was indirect in space. In experimental studies [1, 2], it was established that in nanosystems consisting of germanium QDs located in silicon matrices,
the excitation of spatially indirect excitons (SIE) is possible.
In [3], heterostructures, which are linear germanium QD chains on silicon
substrates, were obtained using the method of electron beam lithography. The average
radii of QD of germanium did not exceed 30 nm. In Ge/Si heterostructures with
germanium QDs, it was established in experimental works [1, 2] that low-temperature
optical absorption and photoluminescence spectra were caused by interband electron transitions from the valence band of germanium QD to the conduction band of
the silicon matrix. The photoluminescence signal of nanostructures in the infrared
spectral region (0.20–1.14) eV was observed up to room temperature [1, 2].
The theory predicts that exciton, containing a hole in QD volume and electron localized above outer spherical interface (QD—silicon matrix), has the binding
energy two orders of magnitude higher than exciton in appropriate bulk semiconductors [4, 5]. Electron and the hole are separated by centrifugal potential, as well as
polarization interaction with a curved interface (QD—silicon matrix) [5]. The energy
S. I. Pokutnyi (B)
Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 17 General
Naumov Street, Kyiv 03164, UA, Ukraine
e-mail: pokutnyi.serg@gmail.com
© Springer Nature Switzerland AG 2021
O. Fesenko and L. Yatsenko (eds.), Nanomaterials and Nanocomposites,
Nanostructure Surfaces, and Their Applications, Springer Proceedings
in Physics 246, https://doi.org/10.1007/978-3-030-51905-6_43
615