The compound with beta-pyrochlore structure with rare for structure type symmetry (orthorhombic, Pnma) has been prepared recently. In polycrystalline sample Rb0.95Nb1.375Mo0.625O5.79 with beta-pyrochlore structure type prepared by solid-state reaction, the diffuse reflection and transmission spectra have been studied. The spectral dependence of the photochromic effect and the temperature dependence of its kinetics have been investigated. It was found that Rb0.95Nb1.375Mo0.625O5.79 is an indirect-gap semiconductor with band gap of 3 eV. A study of the transmission spectrum and a detailed investigation of the photochromic effect made it possible to determine some characteristics of the deep impurity defect level and make a conclusion about the energy ranges in which the Fermi level can be localized in a band gap.

A new series of Dion-Jacobson layered perovskite compounds A’LnNaNb3O10 (A’ = Cs, Rb, H; Ln = Nd, Pr) was synthesized for the first time. Phase and chemical purity of compounds were proved using XRD, SEM, and EDX. Compounds RbNdNaNb3O10, RbPrNaNb3O10, CsNdNaNb3O10 and CsPrNaNb3O10 were synthesized using solid-state reaction, whereas HNdNaNb3O10, HPrNaNb3O10 were obtained by ion-exchange reaction. Crystal structures of solid-state reaction products were refined using the Rietveld method. The plausibility of obtained crystal structures was studied using the bond valence sum (BVS) method. The thermal behavior of compounds was established using DTA. Ion-exchange products were found to be metastable hydrates. The presence of the crystallization water was confirmed by DTA and IR spectroscopy. Optical band gap, electronegativity, valence band (EVB), and conduction band (ECB) potentials of obtained compounds were calculated from diffuse reflectance spectroscopy data. A previously proposed correlation between band gap and structural distortions was confirmed.

Two lead-containing compounds of the Aurivillus family: PbBi2Nb2O9 and PbBi3Ti2NbO12 were synthesized using a conventional high-temperature solid-state (ss) method and ion-exchange (ie) method. The phase and chemical purity of synthesized compounds were confirmed by XRD and EDX, respectively. The second harmonic generation experiment confirmed that all synthesized compounds have a non-centrosymmetric crystal structure. Rietveld refinement of samples prepared by different methods confirmed that ion-exchange and solid-state products share the same crystal structures; however, indirect evidence for different distributions of Pb/Bi between crystallographic positions was observed. Phase transitions, corresponding to the Curie temperatures were detected using high-temperature XRD. Thermal expansion of ion-exchange reaction products was studied in the temperature range of 298-1273 K. The optical band gap, electronegativity, valence band (EVB), and conduction band (ECB) potentials of materials were calculated from UV-vis spectroscopy data. Both PbBi2Nb2O9 (ss) and PbBi2Nb2O9 (ie) can be used for the decomposition of organic molecules under visible light, while PbBi3Ti2NbO12 (ss) and PbBi3Ti2NbO12 (ie) can work only under UV light irradiation due to their wider band gaps.

In polycrystalline sample KNbWO6 with beta-pyrochlore structure type prepared by solid-state reaction, the diffuse reflection and transmission spectra, as well as the spectral, kinetic, and temperature dependencies of the photochromic effect, have been investigated. The energy characteristics of deep and shallow levels in KNbWO6 band gap have been determined. A model explaining the effect of temperature on the behavior of bleaching kinetics in the photochromic effect was suggested.

The electric-field behavior of the resonance features in the photoelectric characteristics of InAs/ GaAs heterostructures is studied. We discuss the emission mechanism of the charge carriers excited from InAs quantum dots into the GaAs matrix. It was shown that at the temperature of liquid nitrogen the photocurrent in a strong transverse electric field is only determined by the effect of electron tunneling through the barrier formed at the quantum-dot interfaces. Comparison of the experimental curves with the quasi-classical expression for the tunneling current component and analysis of the potential structure allowed us to specify some parameters of investigated heterostructures. Analysis of the electric-field dependences of the photocurrent-tunneling component revealed resonance peculiarities connected with the local defect states in the vicinity of InAs/GaAs interface.

Abstract The effect of neutron irradiation on the photosensitivity of the InAs/GaAs quantum dots has been investigated. It was shown that after neutron irradiation with a fluence of 1.5×1015 cm-2 the photosensitivity at the room temperature has been decreased at 3 times, whereas the shape of the photosensitivity’s temperature dependence didn’t reveal any visible changes, despite an appearance of defects in quantum dot layer. The effect was explained by the difficulty of a motion of photoexcited carriers in quantum dot layer to the recombination centres arised after irradiation.

AbstractOn the basis of a comprehensive study of the structural and electronic properties of InAs/GaAs quantum dots grown by vapor-phase epitaxy at atmospheric pressure, a structural model of the quantum dots as three truncated pyramids adjoined at their bases is chosen. The model takes into account the diffusive smearing of the composition near the base and lateral surface as well as the segregation of indium near the vertex. It is established that the wave functions of charge carriers in the ground state are localized in a comparatively small region of the quantum dot near its vertex.

On the basis of a comprehensive study of the structural and electronic properties of InAs/GaAs quantum dots grown by vapor-phase epitaxy at atmospheric pressure, a structural model of the quantum dots as three truncated pyramids adjoined at their bases is chosen. The model takes into account the diffusive smearing of the composition near the base and lateral surface as well as the segregation of indium near the vertex. It is established that the wave functions of charge carriers in the ground state are localized in a comparatively small region of the quantum dot near its vertex.

The electric-field behavior of resonance features of the photoelectric characteristics of InAs/GaAs heterostructures is investigated. The emission of carriers excited by light from InAs quantum dots into the GaAs matrix is ​​discussed. It is shown that at the temperature of liquid nitrogen the photocurrent in a strong transverse electric field is only determined by the effect of electron tunneling through a barrier formed at the quantum-dot interfaces. Comparison of the experimental curves with the results obtained using a quasiclassical expression for the tunneling-current component and subsequent analysis of the potential structure made it possible to refine the parameters of the heterostructure under study. The contribution of the resonance component caused by possible electron tunneling through the barrier with the participation of the local defect states to the total tunneling current is analyzed. The influence of the level of excitation of the system on the photocurrent flowing through the InAs/GaAs heterojunction is theoretically studied.

AbstractA comparative study of the effect of pulsed γ-neutron irradiation on the photosensitivity spectra of Si p – n photodiodes with active layers based on self-assembled GeSi nanoisland arrays and Ge epitaxial layers is performed. The irradiation of photodiodes with GeSi nanoislands is found to not lead to photosensitivity degradation in the spectral region of interband optical absorption in nanoislands (wavelength range of 1.1–1.7 μm). At the same time, a steady decrease in the intrinsic photosensitivity of Si and the photosensitivity of photodiodes based on Ge epitaxial layers with an increase in irradiation dose is observed. This effect is attributed to the accumulation of radiation-induced defects in the Si matrix and deep in Ge epitaxial layers, respectively.

The work focuses on two objectives. First is study of the behavior of electric-resonance features observed in the photovoltaic characteristics of InAs/GaAs heterostructures. Second is identification of the emission mechanism of charge carriers which are excited by light from InAs quantum dots into the GaAs matrix. The photocurrent is defined solely by electron tunneling through the potential barrier at the layers boundary at the presence of a strong electric field. Comparison of the experimental curves with the quasi-classical expression for the tunneling current component and analysis of potential structure have led to the refinement of some parameters of investigated heterostructures and revelation of the resonant component associated with the tunneling of electrons through the barrier with participation of local defect levels at the interface. Theoretical analysis has been carried out to study the effect of the exciting level of the electron subsystem on the photocurrent flowing throw burrier between InAs QD and

A comparative study of the effect of pulsed γ-neutron irradiation on the photosensitivity spectra of Si p–n photodiodes with active layers based on self-assembled GeSi nanoisland arrays and Ge epitaxial layers is performed. The irradiation of photodiodes with GeSi nanoislands is found to not lead to photosensitivity degradation in the spectral region of interband optical absorption in nanoislands (wavelength range of 1.1–1.7 μm). At the same time, a steady decrease in the intrinsic photosensitivity of Si and the photosensitivity of photodiodes based on Ge epitaxial layers with an increase in irradiation dose is observed. This effect is attributed to the accumulation of radiation-induced defects in the Si matrix and deep in Ge epitaxial layers, respectively.

Заращивание массива самоорганизованных квантовых точек InAs/GaAs слоем квантовой ямы InGaAs приводит к увеличению их размера за счет обогащения области вблизи вершины квантовых точек индием, что уменьшает энергию основного оптического перехода в квантовых точках на 50 мэВ и смещает волновую функцию дырки по направлению к вершине квантовой точки. DOI: 10.21883/FTP.2017.11.45088.02

The capping of an array of self-assembled InAs/GaAs quantum dots by an InGaAs quantum-well layer leads to an increase in their size due to indium enrichment of the region near the top of the quantum dots, which decreases the energy of the ground-state optical transition in quantum dots by 50 meV and shifts the hole wave function toward the top of the quantum dot.

The temperature-dependent photosensitivity of InAs/GaAs self-assembled quantum dots at different vertical electric field strengths was studied. The analysis was performed with the help of a theoretical model of the carrier escape process, taking into account the deformation potential and the diffusion broadening of the heterointerface between the InAs quantum dots and the GaAs substrate, as well as excitonic effects. Conducted research allowed to determine the temperature dependence of carriers lifetimes in QDs relatively to the different emission mechanisms at several magnitudes of electric field strengths.

Photoelectric spectra of heterostructures containing InAs quantum dots (QDs) produced in different technological regimes were studied. A simple nondestructive method to reveal a bimodality of the QDs’ size distribution was described. The method based on the analysis of the shape of InAs/GaAs QDs’ photoelectric spectra and their temperature dependencies. The quantitative analysis of the temperature dependencies of the photoelectrical spectra was performed. All possible emission processes occurring from quantum confined levels to the semiconductor matrix were considered at the simulation. The surface concentration of the QDs was estimated.

The fabrication of photodetectors for the wavelength range of communications λ = 1.3–1.55 µm on the basis of Ge/Si(001) heterostructures with thick (~0.5 µm) Ge layers grown by the hot-wire technique at reduced growth temperatures (350°C) is reported. The single-crystal Ga layers are distinguished by a low density of threading dislocations (~105 cm–2). The photodetectors exhibit a rather high quantum efficiency (~0.05 at λ = 1.5 µm and 300 K) at moderate reverse saturation current densities (~10–2 A cm–2). Thus, it is shown that the hot-wire technique offers promise for the formation of integrated photodetectors for the wavelength range of communications, especially in the case of limitations on the conditions of heat treatments.

The systematic features of the inf luence of defect formation during the deposition of a cobalt contact on the optoelectronic characteristics of structures containing InAs/GaAs quantum dots and In x Ga1–x As/GaAs quantum wells are studied. From analysis of the temperature dependences of the photosensitivity of the InAs/GaAs quantum-dot structures, the values of the resultant recombination lifetime of photoexcited charge carriers in quantum dots at different conditions of Co deposition and at different structural parameters are determined.

We investigate the photosensitivity spectra of photodiodes based on Si p-i-n structures with single-layered and multilayer self-assembled GeSi/Si(001) nanoisland arrays in the i region, which are grown using a technique combining Si molecular-beam epitaxy and Ge vapor-phase epitaxy, in dependence on the temperature, diode bias, and GeSi nanoisland parameters. We show that the temperature and field dependences of the diode photosensitivity in the spectral range of the interband optical absorption in GeSi nanoislands are determined by the ratio between the rate of emission of photoexcited holes from the nanoislands and the rate of the recombination of excess carriers in them. We demonstrate the possibility of determination of the hole recombination lifetime in GeSi nanoislands from the temperature and field dependences of the photosensitivity.

The photosensitivity, photoluminescence, and electroluminescence spectra of InGaAs/GaAs diode nanoheterostructures with a Si δ layer formed at a distance of 10 nm from the InGaAs quantum well are studied. The influence of the arrangement of the δ layer with respect to the quantum well on the optoelectronic properties of the structures is established.