Exciton and carrier dynamics in indirect-band-gap semiconductor nanostructures with a type-I band alignment
Final Report Abstract
In this project the novel class of heterostructures (quantum dots (QDs) and quantum wells (QWs)) based on III-V semiconductors with a type-I band alignment and an indirect band gap in the momentum-space has been studied. The basic mechanisms of electron and exciton energy relaxation, their spin dynamics and exciton recombination are investigated by a comprehensive approach comprising sample fabrication, optical spectroscopy and model calculations. The following results are achieved: (1) Molecular-beam epitaxy growth of heterostructures based on gallium, indium and aluminum antimonides (Ga,Al)(As,Sb)/AlAs, (In,Al)(As,Sb)/AlAs, (As,Sb)/AlAs. (2) Spin dynamics of excitons in indirect band gap monolayer QWs in a magnetic field are studied. The emission of GaAs/AlAs QWs is linearly polarized. Two contributions are identified determined by the asymmetry of the QW atomic structure and by the mixing of the heavy and light hole states by a transverse magnetic field. (3) Recombination and spin dynamics of excitons in (In,Al)As/AlAs and (Ga,Al)(As,Sb)/AlAs QWs are investigated in longitudinal and tilted magnetic. The longitudinal g-factor of a heavy hole, the spin relaxation times of an electron and a heavy hole, as well as the factor that determines the radiative recombination of dark excitons and the PL depolarization parameter are measured. (4) The spin structure and spin dynamics of excitons in an ensemble of (In,Al)As/AlAs quantum dots (QDs) with type I band alignment, containing both direct ban gap and indirect band gap QDs are studied. In the direct band gap QDs, the spin dynamics is controlled by anisotropic exchange splitting, and in indirect band gap QDs, by the hyperfine interaction of the electron spin with nuclear spins. The anisotropic exchange splitting of exciton states in direct band gap QDs is measured. (5) The effect of Г-X mixing of electronic states on the anisotropic exchange interaction in direct band gap (In,Al)As/AlAs QDs with type I band alignment is studied. A sharp decrease in the value of the exchange splitting in the region of strong mixing of the wave functions of electrons belonging to the Г and Х valleys of the QD conduction band is found. (6) The hyperfine interaction of spins of electrons and nuclei in indirect-gap (In,Al)As/AlAs QDs with type I band alignment is studied. The theoretical symmetry analysis of the electron Bloch amplitudes in the X valley and the microscopic calculation by the DFT method show that the hyperfine interaction in the X valley is strongly reduced in comparison with the Г valley, and is anisotropic. For the first time, the values of the hyperfine interaction constants of an electron localized in the X valley of the conduction band with three types of nuclei (As, In, and Al) are measured. (7) A new mechanism of spin orientation of localized electrons is discovered: dynamic spin polarization of electrons in interaction with nuclear spin fluctuations. It is shown that fluctuations of the nuclear spin can be used to polarize the angular momentum of electrons through hyperfine interaction in a weak (several millitesla) longitudinal magnetic field. To do this, the sample is illuminated with unpolarized light, which does not directly polarize either nuclei or electrons. (8) In an ensemble with a high density of (In,Al,Ga)As/(Al,Ga)As QDs, the structure of energy levels, recombination of excitons, and spin dynamics of electrons are studied. An optically detected magnetic resonance (ODMR) is realized and g-factor of 1.97 associated with the X valley electrons is measured.
Publications
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Anisotropic exchange splitting of excitons affected by ΓX mixing in (In,Al)As/AlAs quantum dots: Microphotoluminescence and macrophotoluminescence measurements. Physical Review B, 100(20).
Rautert, J.; Rakhlin, M. V.; Belyaev, K. G.; Shamirzaev, T. S.; Bakarov, A. K.; Toropov, A. A.; Mukhin, I. S.; Yakovlev, D. R. & Bayer, M.
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Interface effects on the magnetic-proximity-induced quantized Hall response in heterostructures based on three-dimensional topological insulators. Physical Review B, 99(11).
Men'shov, V. N.; Shvets, I. A. & Chulkov, E. V.
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Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment. Physical Review B, 99(19).
Rautert, J.; Shamirzaev, T. S.; Nekrasov, S. V.; Yakovlev, D. R.; Klenovský, P.; Kusrayev, Yu. G. & Bayer, M.
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Dynamic Polarization of Electron Spins Interacting with Nuclei in Semiconductor Nanostructures. Physical Review Letters, 125(15).
Smirnov, D. S.; Shamirzaev, T. S.; Yakovlev, D. R. & Bayer, M.
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Electron-nuclei interaction in the X valley of (In,Al)As/AlAs quantum dots. Physical Review B, 101(7).
Kuznetsova, M. S.; Rautert, J.; Kavokin, K. V.; Smirnov, D. S.; Yakovlev, D. R.; Bakarov, A. K.; Gutakovskii, A. K.; Shamirzaev, T. S. & Bayer, M.
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Recombination and spin dynamics of excitons in thin (Ga,Al)(Sb,As)/AlAs quantum wells with an indirect band gap and type-I band alignment. Physical Review B, 102(16).
Shamirzaev, T. S.; Yakovlev, D. R.; Bakarov, A. K.; Kopteva, N. E.; Kudlacik, D.; Gutakovskii, A. K. & Bayer, M.
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Dynamic polarization of electron spins in indirect band gap (In,Al)As/AlAs quantum dots in a weak magnetic field: Experiment and theory. Physical Review B, 104(11).
Shamirzaev, T. S.; Shumilin, A. V.; Smirnov, D. S.; Rautert, J.; Yakovlev, D. R. & Bayer, M.
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Exciton recombination and spin relaxation in strong magnetic fields in ultrathin (In,Al)As/AlAs quantum wells with indirect band gap and type-I band alignment. Physical Review B, 104(4).
Shamirzaev, T. S.; Rautert, J.; Yakovlev, D. R. & Bayer, M.
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Optically detected magnetic resonance of indirect excitons in an ensemble of (In,Al,Ga)As/(Al,Ga)As quantum dots. Physical Review B, 104(19).
Ivanov, V. Yu.; Tolmachev, D. O.; Shamirzaev, T. S.; Słupinski, T.; Yakovlev, D. R. & Bayer, M.
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Spin dynamics of charged excitons in ultrathin (In,Al)(Sb,As)/AlAs and Al(Sb,As)/AlAs quantum wells with an indirect band gap. Physical Review B, 106(7).
Shamirzaev, T. S.; Yakovlev, D. R.; Kopteva, N. E.; Kudlacik, D.; Glazov, M. M.; Krechetov, A. G.; Gutakovskii, A. K. & Bayer, M.
