We propose a concept of quantum dot based light emitting diode that produces circularly polarized light without magnetic contacts due to the hyperfine interaction at the crossing of the exciton levels in a weak magnetic field. The electroluminescence circular polarization degree can reach 100%. The concept is compatible with the micropillar cavities, which allows for the generation of single circularly polarized photons. Second order photon correlation function includes information about the nuclear spin dynamics in the quantum dot, and the nuclear spin state can be purified by the quantum measurement backaction.

The effect of thermally generated equilibrium carrier distribution on the vacancy generation, recombination, and mobility in a semiconductor heterostructure with an undoped quantum well is studied. A different rate of thermally generated equilibrium carriers in layers with different band gaps at annealing temperatures forms a charge-carrier density gradient along a heterostructure. The nonuniform spatial distribution of charged vacancy concentration that appears as a result of strong dependence in the vacancy formation rate on the local charge-carrier density is revealed. A model of vacancy-mediated diffusion at high temperatures typical for post-growth annealing that takes into account this effect and dynamics of nonequilibrium vacancy concentration is developed. The change of atomic diffusivity rate in time that follows on the of spatial vacancy distribution dynamics in a model heterostructure with quantum wells during a high-temperature annealing at fixed temperatures is demonstrated by computational modeling.

The vacancy generation dynamics in doped semiconductor heterostructures with quantum dots (QD) formed in the cationic and anionic sublattices of AlAs is studied. We demonstrate experimentally that the vacancy-mediated high temperature diffusion is enhanced (suppressed) in n- and p-doped heterostructures with QDs formed in the cationic sublattice, while the opposite behavior occurs in the heterostructures with QDs formed in the anionic sublattice. A model describing the doping effect on the vacancy generation dynamics is developed. The effect of nonuniform charge carrier spatial distribution arisen in heterostructures at high temperatures on the vacancy generation and diffusion is revealed.

Exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots (QDs) with indirect band gap and type-I band alignment were studied. The negligible (less than 0.2 μeV) value of the anisotropic exchange interaction in these QDs prevents the mixing of the excitonic basis states and makes the formation of spin-polarized bright excitons possible under quasi-resonant, circularly polarized excitation. The recombination and spin dynamics of excitons are controlled by the hyperfine interaction between the electron and nuclear spins. A QD blockade by dark excitons was observed in the magnetic field, that eliminates the impact of nuclear spin fluctuations. A kinetic model which accounts for the population dynamics of the bright and dark exciton states as well as for the spin dynamics was developed to quantitatively describe the experimental data.

New spin-dependent photoemission properties of alkali antimonide semiconductor cathodes are predicted based on the detected optical spin orientation effect and DFT band structure calculations. Using these results, the Na_{2}KSb/Cs_{3}Sb heterostructure is designed as a spin-polarized electron source in combination with the Al_{0.11}Ga_{0.89}As target as a spin detector with spatial resolution. In the Na_{2}KSb/Cs_{3}Sb photocathode, spin-dependent photoemission properties were established through detection of a high degree of photoluminescence polarization and high polarization of the photoemitted electrons. It was found that the multi-alkali photocathode can provide electron beams with emittance very close to the limits imposed by the electron thermal energy. The vacuum tablet-type sources of spin-polarized electrons have been proposed for accelerators, which can exclude the construction of the photocathode growth chambers for photoinjectors.

The energy level structure as well as the exciton recombination and spin dynamics are studied in a dense ensemble of (In,Al,Ga)As/(Al,Ga)As quantum dots (QDs). The band alignment in the QDs is shown to have type-I, indirect character with the lowest electron state at the X valleys of the conduction band and the top hole state in the I' point of the valence band, so that indirect excitons are formed in the QDs. Time-resolved photoluminescence and magnetic-field-induced circular polarization allow us to distinguish electron states belonging to the QDs and the wetting layer. Suppression of the exciton migration within the QD ensemble and along the wetting layer in the magnetic field is found. A pronounced effect of applied microwave radiation on the recombination and spin polarization of the indirect excitons is observed in longitudinal magnetic fields. Optically detected magnetic resonance (ODMR) is detected in both the intensity and the circular polarization degree of the QD emission. The ODMR resonance corresponds to the g factor of 1.97, associated with X-valley electrons. The spin relaxation time of the X-valley electrons is measured to be 600 +/- 25 ns.

A novel spin orientation mechanism - dynamic electron spin polarization has been recently suggested in Phys. Rev. Lett. 125, 156801 (2020). It takes place for unpolarized optical excitation in weak magnetic fields of the order of a few millitesla. In this paper we demonstrate experimentally and theoretically that the dynamic electron spin polarization degree changes sign as a function of time, strength of the applied magnetic field and its direction. The studies are performed on indirect band-gap (In,Al)As/AlAs quantum dots and their results are explained in the framework of a theoretical model developed for our experimental setting.

The exciton recombination and spin dynamics are studied in monolayer-thick (In,Al)As/AlAs quantum wells characterized by an indirect band gap and a type-I band alignment. The exciton recombination time and the photoluminescence intensity are strongly dependent on strength and orientation of an applied magnetic field. In contrast to no effect of an in-plane field, at a temperature of 1.8 K a magnetic field applied parallel to the growth axis drastically slows down the recombination and reduces the intensity of photoluminescence. The magnetic-field-induced circular polarization of photoluminescence is studied as a function of the magnetic field strength and direction, as well as sample temperature. The observed nonmonotonic behavior of these functions is provided by the interplay of bright and dark exciton states contributing to the emission. Taking into account the magnetic-field-induced redistribution of the indirect excitons between their bright and dark states, we evaluate the heavy-hole longitudinal $g$ factor of 3.6, the radiative recombination time for the bright excitons of 0.13 ms, and the nonradiative recombination time of the bright and dark excitons of 0.43 ms, as well as the spin relaxation times of electron of $25\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ and heavy hole of $16\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$, bound in the exciton.

As a result of in situ irradiation in a high-resolution electron microscope, structure modelling, and calculation of images, it is shown that the incorporation of self-interstitial atoms into the extension region of the core of any dislocation is accompanied by their ordering in the form of cluster-like {111}, {001}, and {113} defects, which provide core relaxation. This fact made it possible to visualize for the first time the core structure of undissociated 60° dislocations of two types, glide ( $$60_{{{\text{sh}}}}^{^\circ }$$ ) and sessile ( $$60_{{{\text{gl}}}}^{^\circ }$$ ), which coexist at plastic deformation of Si. It is shown that incorporation of self-interstitial atoms into the dislocation core correlates with an increase of only the D2 line in the photoluminescence spectrum, while perfect sessile a/2〈110〉 dislocations with a core, consisting of paired 5/7-link atomic rings without dangling bonds, are responsible for the rise of the D1 line. This universal core occurs at coalescence of two $$60_{{{\text{sh}}}}^{^\circ }$$ dislocations during their slip in intersecting planes {111}, $$60_{{{\text{sh}}}}^{^\circ }$$ → $$60_{{{\text{gl}}}}^{^\circ }$$ transition, and transformation of a Frank dislocation into a perfect one.

Экспериментально и теоретически изучалось сверхтонкое взаимодействие электронов и ядер в непрямозонных КТ (In,Al)As/AlAs первого рода. Особенностью этих непрямозонных КТ является пренебрежимо малое анизотропное обменное взаимодействие электрона в Х долине и дырки в Г долине, что приводит к формированию экситонов, с «чистыми» спиновыми состояниями |±1>, рекомбинирующих с излучением циркулярно-поляризованных фотонов. Для экспериментального определения электрон-ядерного взаимодействия измерялась циркулярная поляризация фотолюминесценции КТ в поперечном (эффект Ханле) и продольном (эффект восстановления циркулярной поляризации PRC) магнитных полях. Фотолюминесценция непрямо-зонных КТ возбуждалась квазирезонансно, через возбужденные состояния электрона, принадлежащие Г долине зоны проводимости циркулярно-поляризованым излучением Ti:Sapphire лазера.

The circularly polarized cathodoluminescence (CL) technique has been used to study the free spin-polarized electron injection in semiconductor heterostructures with quantum wells (QWs). A polarized electron beam was created by the emission of optically oriented electrons from the p-GaAs(Cs,O) negative electron affinity (NEA) photocathode. The prepared beam was injected in a semiconductor QW target, which was activated by cesium and oxygen to reduce the work function. To study the spin-dependent injection, we developed a spin-detector prototype, which consists of a compact proximity focused vacuum tube with the source and target placed parallel to each other on the opposite ends of the vacuum tube (photodiode). The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range of 0.5-5.0 eV and temperature in the range of 90-300 K was studied. The CL was polarized to 2 % by the injection of 20 % spin-polarized electron beam with the energy of 0.5 eV at room temperature. The asymmetry (Sherman function) of spin detection was estimated. It was shown that the dependence of the CL polarization degree on the injected electron energy is satisfactory described by the model that considers the electron spin relaxation in the heterostructure matrix and QWs. The results demonstrate that semiconductor detectors are promising for the spin-polarimetry applications based on the optical detection of free-electron spin polarization.

We suggest a new spin orientation mechanism for localized electrons: dynamic electron spin polarization provided by nuclear spin fluctuations. The detrimental effect of nuclear spin fluctuations can be harnessed and employed to provide angular momentum for the electrons via the hyperfine interaction in a weak magnetic field. For this, the sample is illuminated by an unpolarized light, which directly polarizes neither the electrons nor the nuclei. We predict that, for the electrons bound in localized excitons, 100% spin polarization can be reached in longitudinal magnetic fields of a few millitesla. The proof of principle experiment is performed on momentum-indirect excitons in (In,Al)As/AlAs quantum dots, where in a magnetic field of 17 mT the electron spin polarization of 30% is measured.

The electron-nuclei hyperfine interaction of electrons in indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment has been experimentally studied by measuring the polarization degree of the photoluminescence in a transverse magnetic field (Hanle effect) and the polarization recovery in a longitudinal magnetic field. The different symmetries of the $X$ valley electron Bloch amplitudes at the As, In, and Al nuclei strongly affect the hyperfine interaction. The hyperfine constants corresponding to these nuclei have been determined.

The dynamics of exciton recombination and spin relaxation in thin (Ga,Al)(Sb,As)/AlAs quantum wells (QWs) with indirect band gap are studied. The band alignment in these QWs is identified as type I. The exciton recombination time exceeds hundreds of microseconds, while the spin relaxation times of the electron and the heavy hole in an exciton do not exceed hundreds of nanoseconds. The heavy-hole longitudinal $g$ factor is determined to be $+2.5$. Despite the long exciton lifetimes, the photoluminescence circular polarization degree induced by a magnetic field is unexpectedly small and does not exceed $25%$.

Type-I indirect-gap heterostructures are convenient objects for studying the spin dynamics of localized excitons, which are difficult to investigate in heterostructures of other types. It is shown that structures with such an energy spectrum can be formed from III–V binary compounds on substrates with the (110) orientation. The effect of the strain distribution and conduction-band structure in quasimomentum space on the energy spectrum of electronic states in the heterostructures is discussed.

AbstractType-I indirect-gap heterostructures are convenient objects for studying the spin dynamics of localized excitons, which are difficult to investigate in heterostructures of other types. It is shown that structures with such an energy spectrum can be formed from III–V binary compounds on substrates with the (110) orientation. The effect of the strain distribution and conduction-band structure in quasimomentum space on the energy spectrum of electronic states in the heterostructures is discussed.

The exciton dynamics in transverse magnetic field is investigated both experimentally and theoretically in two-monolayer-thick GaAs/AlAs quantum wells with an indirect band gap and a type-II band alignment. The observed linear polarization of the quantum well photoluminescence has two contributions, one of which arises from the crystalline structure of the quantum well. It does not depend on temperature and demonstrates a strong spectral dependence across the emission band. The other one is induced by a transverse magnetic field. It strongly decreases with increasing temperature, has no spectral dependence, and demonstrates an unexpectedly long-time dynamics. The experimental findings can be explained in the framework of the developed theoretical model which accounts for the quantum well anisotropy, the Zeeman effect of electrons and holes in the transverse magnetic field, and the redistribution of excitons over the spin sublevels. It provides quantitative agreement with the experiment and allows us to evaluate, for the studied structure, the heavy-hole in-plane $g$-factor tensor, which turns out to be extremely anisotropic with principal values of opposite signs and the same magnitude of 0.25.

Molecular-beam epitaxy is used to produce GaP/Si hybrid substrates that allow the growth of highly efficient light-emitting heterostructures with GaAs/GaP quantum wells. Despite the relatively high concentration of nonradiative-recombination centers in GaP/Si layers, GaAs/GaP quantum-well heterostructures grown on GaP/Si hybrid substrates are highly competitive in terms of efficiency and temperature stability of luminescence to similar heterostructures grown on lattice-matched GaP substrates.

AbstractMolecular-beam epitaxy is used to produce GaP/Si hybrid substrates that allow the growth of highly efficient light-emitting heterostructures with GaAs/GaP quantum wells. Despite the relatively high concentration of nonradiative-recombination centers in GaP/Si layers, GaAs/GaP quantum-well heterostructures grown on GaP/Si hybrid substrates are highly competitive in terms of efficiency and temperature stability of luminescence to similar heterostructures grown on lattice-matched GaP substrates.