Вычислены времена каскадного захвата электрона на заряженный диполь донор-акцептор для случая импульсного и стационарного возбуждений примесной фотопроводимости в GaAs, Ge и Si. Показано, что при концентрации заряженной примеси, большей 1013 см-3, зависимость частоты каскадного захвата от концентрации заряженной примеси становится сублинейной в рассматриваемых полупроводниках. DOI: 10.21883/FTP.2017.11.45098.12

The times of the cascade capture of electrons at a donor–acceptor charged dipole for the case of the pulsed and steady-state excitation of impurity photoconductivity in GaAs, Ge, and Si are calculated. It is shown that the dependence of the frequency of the cascade capture on the concentration of the charged impurity becomes sublinear in semiconductors under consideration at a concentration of the charged impurity higher than 1013 cm–3.

The processes associated with the transfer of excitonic excitations between tunnel-uncoupled quantum wells (QW) and the influence of the local electric field were investigated in AlGaAs/GaAs heterostructures by the method of photoluminescence excitation (PLE) spectroscopy at low (4.2 K) temperature. The variation in the intensity of photoluminescence (PL) from the wider QW under resonant excitation of excitonic transition in the adjacent narrow QW has been observed. The difference in the PL maximum position and intensity of the wider QW under resonance excitation of the narrow one is explained by the influence of quantum-confined Stark effect on the process of exciton recombination.

The times for the cascade capture of an electron by a charged impurity have been calculated for pulsed and stationary excitations of impurity photoconductivity in GaAs and InP. The characteristic capture times under pulsed and continuous excitations are shown to differ noticeably both from each other and from the value given by the Abakumov–Perel–Yassievich formula for a charged impurity concentration greater than 1010 cm–3. The cause of this difference has been established. The Abakumov–Perel–Yassievich formula for the cascade capture cross section in the case of stationary excitation has been generalized. The dependences of the cascade capture rate on the charged impurity concentration in GaAs and InP have been found for three temperatures in the case of pulsed excitation.

В гетероструктурах AlGaAs/GaAs методом спектроскопии возбуждения фотолюминесценции исследовались процессы, связанные с переносом экситонных возбуждений между туннельно-несвязанными квантовыми ямами и изменением встроенного электрического поля. Наблюдалось изменение интенсивности сигнала низкотемпературной фотолюминесценции (при 4.2 K) из более широкой квантовой ямы при совпадении кванта энергии лазера накачки с энергией экситонного перехода в узкой яме. Изменение положения максимума и интенсивности фотолюминисценции из более широкой квантовой ямы при возбуждении вблизи экситонных резонансов в узкой квантовой яме объясняется влиянием квантово-размерного эффекта Штарка на процесс экситонной рекомбинации.

A multifunction setup for coherent optical spectroscopy with excitation of semiconductor structures in a wavelength interval of 750–1800 nm and a time resolution of about 100 fs is presented. Minor adjustments are needed for the measurements of photoluminescence kinetics, photon echo, and four-wave mixing under excitation of samples using time-correlated series of femtosecond laser pulses. Results of optical experiments are presented.

The effect of the near-field interaction of shallow donors in GaAs on the intracenter absorption spectrum of impurities has been considered. It has been shown that the near-field interaction leads to broadening of the absorption line, which increases with the donor density. The absorption line shape is no longer Lorentzian: its low-frequency wing becomes more prolonged than the high-frequency wing.

Our objective is to study Raman spectra from 74Ge isotope enriched nc-Ge/amorphous-Ge structures, given the expected minimal influence of the matrix on the nanocrystalline phase in the structures with a modified isotope composition. We also assess the potential of plasma-enhanced chemical vapor deposition for producing germanium nanocrystals in the amorphous matrix from germanium tetrafluoride enriched with 74Ge isotope. The nanocrystal phase was formed by annealing the samples in different conditions. The nc-Ge peak width and position in the Raman spectrum agree well with the theoretical data. The out-of-plane elastic strain of the nc-Ge lattice in the annealed structures, estimated from the shift of the Ge (111) and (220) diffraction peaks, was of the order of 1∙10−3.

We experimentally observed an increase in the intensity of photoluminescence from a wider quantum well (QW) when an exciton transition was induced in the neighboring narrower QW separated from the former one by a tunneling-nontransparent AlGaAs barrier. The dependence of the efficiency of the near-field radiative transfer of excitons on the distance between QWs was studied in heterostructures without coincidence of exciton resonances in the adjacent QWs. Theoretical results were qualitatively consistent with the available experimental data.

We report a study into the process of energy transfer between quantum wells divided by 30-nm-thick opaque barriers. It was experimentally observed that the intensity of a photoluminescence signal from a quantum well increased by 15% under resonant excitation of exciton transition in the adjacent quantum well. The quantum wells were 30 nm apart. A radiative mechanism of energy transfer in the near-field region of emitting exciton is proposed. Within this theoretical model, the efficiency of the energy transfer decreases by a power law with greater distance between the quantum wells. The theory is found to be in qualitative agreement with the experimental results.

The experimental results of a photoluminescence kinetics study of InAs/GaAs structures with quantum dots grown by metal-organic vapor-phase epitaxy are shown. The measurements have revealed the fast capture of excited carriers from the GaAs barrier to quantum dots and slow interlevel relaxation inside the quantum dots.

A new approach for producing high-purity silicon with isotopic enrichment of Si-28 isotope is reported. The methods of centrifugal enrichment were modified to obtain the initial gaseous silicon tetrafluoride with a record-breaking enrichment of 0.99999664(11) with respect to Si-28. The effective conversion of silicon tetrafluoride into elementary silicon with minimal isotopic dilution was achieved in an electron cyclotron resonance discharge plasma, sustained by gyrotron microwave radiation with a frequency of 24 GHz. We have experimentally demonstrated the deposition of the layers of microcrystalline Si-28 with enrichment of 0.999986 +/- 0.000003, which is the best result at the present time. (C) 2012 Elsevier Ltd. All rights reserved.

The results of experimental studies of the subpicosecond relaxation dynamics of photoexcited charge carriers in an In 0.22 Ga 0.78 As/GaAs quantum-well heterostructure are reported. From photoluminescence studies of the structure by the upconversion technique, the cooling rate of charge carriers in the quantum well and the time of charge-carrier trapping into the well are estimated to be ∼1 ps at 300 K and at ∼6.5 ps at 10 K.

In this paper we report a study on relaxation of the impurity photoresponse in strained p-Ge/GeSi heterostructures excited by pulsed THz radiation. The relaxation time is found to increase with the applied dc electric field, which is interpreted within the model of cascade carrier capture by the impurity centers. A second time scale of the impurity photoconductivity relaxation is observed near the impurity breakdown field, and in post-breakdown electric fields the relaxation time (decreasing with the field) is shown to be governed by the impact ionization rather than by the recombination.

Processes occurring when a static transverse electric field is applied to a GaAs/AlGaAs n - i - n heterostructure with single quantum wells and asymmetric tunnel-coupled double quantum wells have been investigated by optical methods. The difference between the energies of exciton transitions for quantum wells of different widths makes it possible to attribute the observed photoluminescence peaks to particular pairs of wells or particular single quantum wells. The local electric field for each quantum well has been determined in terms of the Stark shift and splitting of exciton lines in a wide range of external voltage. A qualitative model has been proposed to explain the nonmonotonic distribution of the electric field over the depth of the heterostructure.

The paper presents the theoretical investigation of the Fano resonance in the spectra of impurity photocurrent for bulk semiconductors doped with donors. Calculation is made for the parameters describing the Fano resonance. These parameters can be evaluated with the use of two general dimensionless functions that are calculated numerically. Two kinds of donor impurity are considered: a hydrogen-like charged center and an impurity influenced by the central cell potential.

The Purcell effect, acceleration of a spontaneous emission recombination rate, has been observed in InN/In nanocomposites with buried nanoparticles of metallic In. This effect, associated with localized plasmons, is characterized by the averaged Purcell factor as high as 30-40 in the structures with large enough particles. This high value is indicative of a noticeable contribution from the emitting dipoles polarized normally to the nanoparticle surface in this system. The experimental observation of shortening of the emission lifetimes with increasing the amount of In is supported by calculations performed in a semiclassical approximation.

The photocurrent spectra of p -GaAs samples and a p -InGaAs/GaAsP quantum-well heterostructure doped with shallow acceptors (C, Be, Zn) are investigated. Fano resonances associated with the ground and excited acceptor states are revealed and analyzed. It is found that sharp change in dielectric constant in the GaAs reststrahlen region strongly affects the lineshape of the Fano resonance associated with the acceptor ground state.