Photoluminescence (PL) spectra have been studied in 3C-SiC/4H-SiC heterostructures and 3C‑SiC single crystals. It was shown that epitaxial 3C-SiC layers grown on 4H-SiC substrates have a markedly poorer crystal perfection than do 3C-SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3C-SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3C-SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

AbstractPhotoluminescence (PL) spectra have been studied in 3 C -SiC/4 H -SiC heterostructures and 3 C ‑SiC single crystals. It was shown that epitaxial 3 C -SiC layers grown on 4 H -SiC substrates have a markedly poorer crystal perfection than do 3 C -SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3 C -SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3 C -SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

The influence of non-uniform distribution of spin density in the temperature range from 5 to 80 K under the conditions of optical orientation of electrons in semiconductors is analyzed. Possibility to determine the kinetic parameters of carriers by depolarization of recombination radiation in a magnetic field is shown. Electron diffusion length and mobility is defined for materials with a hole conductivity. An estimated value of the rate of recombination on a free surface and its influence on the distribution of the concentration of non-equilibrium electrons from the excitation surface into the bulk is presented.

Исследованы спектры поглощения ионов Er3+, внедренных в матрицу AlN. Примесь эрбия вводилась в объемные кристаллы AlN диффузией. В спектральном диапазоне 370-700 nm наблюдались линии поглощения, связанные с внутриконфигурационными электронными f-f-переходами из основного 4I15/2-состояния на уровни возбужденных состояний ионов Er3+. При температуре T=2 K детально исследованы переходы на уровни состояний 4F9/2, 2H11/2, 4F7/2, 4F5/2, 2H9/2 и 4G11/2. Количество наблюдавшихся линий для указанных переходов полностью совпадает с теоретически возможным для электронных f-f-переходов в ионах Er3+, находящихся в кристаллическом поле с симметрией ниже кубической. Узость наблюдавшихся линий и их число убедительно свидетельствуют о замещении ионами эрбия преимущественно одной регулярной кристаллической позиции. Наиболее вероятным представляется внедрение Er3+ в позицию Al3+ с локальной симметрией C3v. Определены энергетические положения уровней возбужденных состояний для исследованных переходов. Построена схема уровней энергии ионов Er3+ в кристаллах AlN. DOI: 10.21883/FTT.2017.12.45236.175

The absorption spectra of the Er3+ ions embedded in the AlN matrix have been investigated. The admixture of erbium was introduced in bulk AlN crystals by diffusion. The absorption lines, which are associated with the intraconfigurational electronic f–f-transitions from the ground 4 I 15/2-state to the levels of ion Er3+ excited states have been observed in the spectral range of 370–700 nm. The transitions to the state levels 4 F 9/2, 2 H 11/2, 4 F 7/2, 4 F 5/2, 2 H 9/2, and 4 G 11/2 have been investigated in detail at the temperature T = 2 K. The number of the observed lines for these transitions coincides with the theoretically possible one for the electronic f–f-transitions in the ions Er3+, which are in the crystal field with the symmetry below cubic. The narrowness of the observed lines and their number convincingly testify the replacement of preferably one regular crystalline position by erbium ions. The implementation of Er3+ in the Al3+ position with the local symmetry C 3v appears the most probable. The energy positions of the levels of excited states for the investigated transitions have been determined. The diagram of the Er3+ ion energy levels in the AlN crystals has been built.

Hydride vapor phase epitaxy (HVPE) growth of semipolar AlN and GaN layers on planar Si(100) substrates with SiC nanolayer is investigated. It is shown experimentally that the solid-phase epitaxial formation of a specially oriented SiC nucleation layer followed by epitaxy of AlN layer by HVPE at low rates enables growth of aluminum and gallium nitrides in the semipolar direction. For the best GaN(20-23) layers obtained, the full width at half maximum (FWHM) value for the x-ray diffraction rocking curve is 24 arcmin. The photoluminescence spectrum of the semipolar GaN measured at 4 K exhibits bands related to basal-plane and prismatic stacking faults (BSF and PSF).

The spin dynamics of localized donor-bound electrons interacting with the nuclear spin ensemble in n-doped GaAs epilayers is studied using nuclear spin polarization by light with modulated circular polarization. We show that the observed build-up of the nuclear spin polarization is a result of competition between nuclear spin cooling and nuclear spin warm-up in the oscillating Knight field. The developed model allows us to explain the dependence of nuclear spin polarization on the modulation frequency and to estimate the equilibration time of the nuclear spin system that appears to be shorter than the transverse relaxation time T_2 determined from nuclear magnetic resonance.

This Letter presents results of analysis of the absorption spectra of AlN:Er3+ bulk crystals. In the spectral of 370–700 nm, absorption lines responsible for intraconfiguration electron transition from the ground state 4I15/2 to the excited states of Er3+ ions are found. Transitions to the levels of the 4F9/2, 2H11/2, and 4G11/2 states at 2 K are studied in detail. The number of observed lines for these transitions fully agrees with that theoretically possible for f–f electron transitions in Er3+ ions found in a noncubic crystal field. The small width of the observed lines and their number indicate that erbium ions displace mostly one regular crystal position. Most probably, Er3+ occupies the position of Al. Energy positions of excited states for the considered transitions are determined.

The f–f absorption and emission spectra of Er3+ impurities were observed and identified in KTaO3 and K1 – x Li x TaO3 single crystals. It was shown that Li off-centers related random fields markedly influence intensity, width and position of zero-phonon lines. The detail analysis of the absorption spectra obtained allowed one to determine energies of the Stark sublevels of excited states for Er3+ dominant centers of noncubic symmetry.

Carrier-recombination dynamics is studied by the method of optical orientation at room temperature in the active layer of a laser diode structure. The dependence of the degree of electron-spin orientation on the excitation density is attributed to saturation of the nonradiative-recombination channel. The time of electron capture at recombination centers is determined to be τ e = 5 × 10–9 s. The temperature of nonequilibrium electrons heated by a He–Ne laser is estimated.

We have studied epitaxial layers of gallium nitride (GaN) in a template composition grown by surfactant-mediated hydride-chloride vapor phase epitaxy. The surfactant component was provided by 5 mass % additives of antimony and indium to the source of gallium. Comparative analysis of the obtained results shows evidence of the positive influence of surfactants on the morphology of epitaxial GaN layers.

Results of a detailed study of optical absorption and photoluminescence of slightly erbium-doped (~50ppm) strontium titanate (SrTiO3) single crystals are presented. This study allowed us to specify the structure of energy levels that determine the main internal optical transitions within the 4f11 electron configuration of Er3+ ions in SrTiO3:Er crystals at temperatures below the transition from cubic to tetragonal phase. The numbers of energy levels of the studied multiplets obtained at 2K correspond exactly to the theoretically expected numbers of crystal field levels for multiplets of only one type of Er3+ centers with non-cubic symmetry. Experimental results indicate that Er3+ ions most probably substitute for Sr2+ ions acting in SrTiO3 as ionized donors. Such location of Er3+ ions is consistent with both n-type conductivity and substantial free charge carrier absorption in the infrared spectral region observed in the studied SrTiO3:Er single crystals at room temperature.

This paper presents the results of complex measurements of the microphotoluminescence spectra of quantum-well structures based on InGaN/GaN〈Sm〉 and the determination of the concentration and charge state of the Sm dopant. It has been shown that an increase in the magnetic field strength and the excitation intensity of the microphotoluminescence spectra leads to an increase in the luminescence intensity and a shift in the position of the maximum of the emission wavelength toward the short-wavelength region of the spectrum. Measurements of the microphotoluminescence spectra with variations in the external magnetic field strength, as well as with the introduction of paramagnetic and magnetic impurities, provide additional information on the mechanisms of formation of luminescence spectra in the quantum-well structures InGaN/GaN〈Sm〉,〈Eu + Sm〉. In the long-wavelength region, the influence of the magnetic field on the shape of the microphotoluminescence spectra of the InGaN/GaN structures doped with Sm and Sm + Eu is less pronounced than that in the short-wavelength region.

The optical absorption spectra of Li6Y(BO3)(3):Er3+ crystals have been studied. The absorption lines corresponding to intraconfiguration electronic transitions from the I-4(15/2) ground state to the levels of excited states of Er3+ ions have been found in the spectral range of 370-700 nm. The transitions to the F-4(9/2), S-4(3/2), H-2(11/2), F-4(7/2), F-4(5/2), F-4(3/2), H-2(9/2), and (4)G(11/2) levels have been investigated in detail at 2 K. The number of lines observed for these transitions corresponds to the theoretical maximum for the f-f electronic transitions in Er3+ ions located in the noncubic crystal field. The narrowness of the lines observed and their number indicate that erbium occupies one regular position (specifically, the yttrium position). The energy levels of the excited states have been determined for the transitions under study.

Features of the creation of gallium arsenide (GaAs) p-i-n structures on germanium substrates are considered. Optimum regimes for growth of thick GaAs layers by hydride-chloride vapor phase epitaxy (HVPE) on Ge substrates are established, which allow high-quality p-i-n structures with characteristics close to those reached by homoepitaxy to be obtained. The spectra of exciton photoluminescence have been measured for ultrahigh-purity GaAs layers of various thicknesses grown under differing HVPE conditions.

The degree of circular polarization of the photoluminescence of samples with GaAs/AlGaAs quantum wells grown with growth interruption at both interfaces and under conventional growth conditions has been investigated. It has been revealed that, at a low measurement temperature (4.2 K), the values of the circular polarization measured at different detection energies within the spectral profile of the luminescence band differ substantially for the sample grown with the growth interruption, whereas this effect is not observed for the sample grown without growth interruption. An increase in the sample temperature to 77 K leads to the disappearance of the effect under consideration. The observed behavior has been explained in terms of the model that accounts for a significantly different degree of localization of charge carriers in the growth islands (formed at the interfaces of the structure) with the spatial sizes determined by the specific growth conditions of the sample.

A setup is developed for measuring the spectra of wideband semiconductors (III nitrides) and related heterostructures. The setup makes it possible to trace the time distribution of the luminescence intensity at a fixed wavelength with a resolution of ±5 ns and a sampling rate of up to 10 MHz in the time interval from several microseconds to several hundreds of microseconds. Also, it plots the integral intensity of luminescence versus the wavelength. Precision measurement conditions are provided.

Europium monophthalocyanine Eu(acac)Pc, europium monotetranitrophthalocyanine Eu(acac)Pc(NO 2 ) 4 , and heteroleptic europium tetranitrobisphthalocyanine Eu(Pc)(Pc(NO 2 ) 4 ) are synthesized. The spectral characteristics of the phthalocyanine complexes in the visible and near-infrared regions are studied. The photoluminescence spectra are recorded. The luminescence bands are detected in the regions 450–500 nm (S 2 → S 0 ) and 670–730 nm (S 1 → S 0 ). The peaks are attributed to electronic transitions in the organic ligands.