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Using the density functional theory and the generalized gradient approximation, we calculated the atomic structure, the density of electronic states, and the optical absorption spectra of CdS quantum dots containing intrinsic defects — a cadmium vacancy VCd and an interstitial sulfur atom SI, and substitutional impurities — zinc and copper in place of the atom cadmium — ZnCd and CuCd, respectively. The calculations were performed for the Cd33S33 cluster corresponding to the so-called “magic” size of the quantum dot. This size has a minimum of dangling bonds at the surface and allows the using of such a cluster without the passivation. The structural relaxation during the formation of such defects and the distribution of the wave function of the state corresponding to the top of the valence band are analyzed in details. It has been shown that the cadmium vacancy forms local states in the band gap of CdS nanocrystals, and can serve as centers of radiative recombination. Other defects form energy levels in the depths of the valence band or near its top, but whose energy positions do not correspond to the band maxima in the experimental photoluminescence spectra of CdS quantum dots, both undoped and doped with zinc. The calculated optical absorption spectra demonstrate a strong peak in the region of fundamental absorption of CdS for a cluster containing a substitutional impurity of CuCd, in contrast to other systems where no such peaks are observed. In addition, the replacement of the cadmium atom with copper leads to a decrease in the number of chemical bonds to three and, accordingly, to the largest relaxation among the systems studied. This feature is caused by the crystal structure inhomogeneity of copper sulfide CuxS, which, depending on stoichiometry, can be either a semiconductor or a metal.

The physicochemical properties of low-dimensional structures based on CdTe obtained are investigated by the method of colloidal synthesis. The analysis of the optical absorption spectra and the luminescence intensity of the CdTe colloidal NCs showed that the nature of the dispersion medium significantly affects their optical properties. The optical absorption spectra of the CdTe NK fractions obtained by dissolving the flocs in deionized water and in deionized water with the addition of NaOH have been shown to have the same character. However, the addition of NaOH results in a shift of the absorption maximum by 8-12 nm into the longwave region. This suggested that the addition of NaOH to the colloidal solution of NK CdTe during sedimentation deposition leads to the aggregation of cadmium telluride particles. The addition of NaOH results in the quenching of photoluminescence. It can be assumed that during the sedimentation deposition there is a leaching of THC to a critical concentration, therefore, due to insufficient stabilization of the surface of the NC CdTe, a rapid aggregation of particles occurs and a loss of sedimentation stability of the solution is observed, which causes the PL quenching. The analysis of the optical absorption and photoluminescence spectra of the fractions of the colloidal solution of NC CdTe obtained by using DMF as a dispersion medium during the sedimentation deposition leads to the conclusion that the nature of the dispersion medium significantly affects the optical properties of CdTe NC. The maxima of the OP spectra corresponding to the first exciton transition of all fractions are shifted to the longwave region and change their shape compared to the corresponding spectra for the aqueous fractions. In this case, the PL intensity of the first and second fractions of CdTe NC in DMF is approximately 100 ppm. exceeds the PL intensity of the aqueous fractions, which can be explained by the fact that DMF, unlike deionized water, does not wash out THC from the surface of the CdTe NC.

Structural and electronic characteristics of neutral and charged vacancies of cadmium and sulfur in CdS nanocrystals have been performed using the density functional method with hybrid exchange-correlation functional. Total and partial density of states, formation energies and the energies of thermodynamic transitions were calculated. Based on these theoretical findings and available experimental data, we can confirm the assumption, that the singly charged vacancies of cadmium are the centers of radiative recombination in such the structures. Key words: Cadmium sulfide, nanocrystal, photoluminescence, vacancy, density functional method.

Surface and optical properties of CdTe nanoparticles obtained by grinding (40-150 nm, microcrystals) and colloidal synthesis (1-4 nm, nanocrystals) methods are investigated. It is shown that the most intensive adsorption of stabilizer molecules on the CdTe surface occurs when solvents are better wetting the surface of CdTe particles. It is found that the best stabilization of both the micro- and nanocrystals of CdTe is provided by using methyl and ethyl alcohol as the dispersion medium. The basic characteristics of photoluminescence of CdTe nanocrystals stabilized with thioglycolic acid in deionized water, methanol and ethanol of various concentrations are reported.

We study theoretically the excitonic emission properties of a hybrid nanosystem composed of a spherical metal nanoparticle (NP) and a spherical quantum dot (QD). We show that electromagnetic field (EMF) emitted by a single QD has only dipole, quadrupole, and octupole components, i.e., QD cannot in principle be regarded as an oscillating point dipole, which emits infinite series of multipoles. This leads to a substantial deviation of the characteristics of QD excitonic emission from the emission characteristics of point dipole (molecular fluorophore) located in a vicinity of metal NP at small interparticle distances. The observed fluorescence spectra of the CdTe QD/Ag NP nanostructure are found to be in good agreement with the calculated ones.

Effect of microwave radiation (24 GHz) on transformation of impurity-defect complexes in CdTe:Cl single crystals within the spectral range 1.3–1.5 eV was studied using the low-temperature ( T =2 K) photoluminescence (PL) technique. The shapes of donor–acceptor pairs (DAP) and Y PL bands were studied in detail. The Huang–Rhys factor was calculated for the DAP luminescence depending on microwave radiation treatment. The increase of the distance between the DAP components responsible for emission at 1.455 eV and the quenching of Y-band due to microwave irradiation were observed. The method to decrease the amount of extended defects in near-surface layers of CdTe:Cl single crystals has been proposed.

Using stabilizers and promoters we have obtained colloidal CdTe nanocrystals (NCs) in aqueous solutions. Incorporation of the CdTe NCs into polymer films has been fulfilled subsequently. It is shown that the use of vinyl acetate-acrylate copolymer as the matrix material for CdTe NC incorporation from colloidal solutions allows to get stable and nontoxic nanoheterogeneous film structures, which are characterized by satisfactory values of the photoluminescence quantum yield. Photoluminescence characteristics of the studied materials have been analyzed. Keywords: cadmium telluride, nanocrystal, vinyl acetate-acrylate copolymer, photoluminescence spectra, photoluminescence quantum yield.

Semiconductor Hg3In2Te6 crystals and their analogous are solid solutions of In2Te3 and HgTe. Hg3In2Te6 crystals are congruently melted as chemical compound. Like In2Te3 the Hg3In2Te6 crystal has cubic crystal lattice with stoichiometric vacancies in their crystal structure. The electroconductivity, photoconductivity, mechanical, chemical properties of the crystals do not deteriorate after their irradiation by γ-photons with energies up to 1 MeV and doses up to 1018 cm-2 , by electrons with energies up to 300 MeV and doses up to 1019 cm-2 and by mixed reactor irradiation (filtered slow neutrons) with doses up to 1019 cm-2 [1,2]. This feature is determined by high concentration (~1021 cm-3) of stoihiometric vacancies (Vs) in crystal structure, where every third In-cation node is empty. These Vs are electroneutral, they capture all impurity atoms in these crystals and kept them in electroneutral state too. On the other hand this feature doesn't allow to form direct p-n junctions in these crystals by introducing the impurities. However, we have developed p-n junction analogues in form of Schottki diodes and corresponding photodiodes with semitransparent metal layer on single crystal Hg3In2Te6 substrate that allows irradiation to get into active region preserving this way all the advantages compared to p-n junction.

The effect of microwave radiation on the luminescence properties of CdS and CdTe:Cl single crystals is studied. It is established that the exposure of these semiconductors to short-term (≤30 s) microwave radiation substantially modifies their impurity and defect structure. The mechanisms of transformation of the defect subsystem of II–VI single crystals upon microwave treatment are discussed. It is shown that the experimentally observed changes are defined by the nonthermal effects of microwave radiation at a power density of 7.5 W cm–2; at 90 W cm–2, nonthermal effects are prevailing.

A new method for formation of the cross-linked polymer films at the solid surface as well as the thin nanocomposite films based on them with embedded CdS nanocrystals is reported in this paper. The process involves several stages, namely, (i) thin polymer film formation on glass slide by spin coating of an organic solution of reactive peroxide-containing copolymer (RC), polyethylene glycols (PEG) of various molecular weight, and cadmium acetate [Cd(Ac)2] as nanocrystal precursor; (ii) melting and cross-linking of the polymer film; and (iii) synthesis of CdS nanocrystals inside the polymer film via sol–gel technique. The X-ray diffraction analysis and UV–visible spectroscopy prove formation of the CdS nanocrystals in the thin polymer films. This method allows forming multilayered nanocomposite films with tuned properties. The obtained results reveal that size of the CdS nanocrystals and optical properties (absorption and photoluminescence spectra) of the nanocomposite films depend on the nature of polymer matrix, PEG/RC ratio, Cd(Ac)2 concentration, and the number of layers composing the films.

A colloidal suspension method is used to obtain CdTe nanocrystals modified with thioglycolic acid in aqueous solutions of ethylene glycol. Their photoluminescence spectrum is shifted to shorter wavelengths relative to that of CdTe nanocrystals synthesized in water. It is found that the ethylene glycol molecules participate in the stabilization of the nanocrystals and passivation of surface defects, with an optimum concentration of 10% ethylene glycol in the reactive mixture for production of stably dispersed CdTe. It is difficult to observe plasmon effects in these nanoparticles when Ag nanoparticles are present because cadmium iodide is used as a precursor salt, which leads to the appearance of I2, an oxidant for Ag nanoparticles, in the solution. When a protective polyelectrolyte intermediate layer of thickness ~11.7 nm is deposited on a colloidal silver substrate, the photoluminescence intensity of the CdTe nanoparticles increases by a factor of 1.7. The chemical features of these nanoparticle solutions cause their luminescence characteristics to be highly sensitive to the presence of Ag nanoparticles in the solution. Changes in the position and intensity of the photoluminescence peak are observed for concentrations of Ag nanoparticles in the solution as low as 10–11 mol/l.

Photoelectric Properties of Heterostructures with Oxide Films Containing Si(Ge) Quantum Dots Formed by Pulsed Laser Deposition A. V. Sachenko1, D. V. Korbutyak1, Yu. V. Kryuchenko1 ∗, E. B. Kaganovich1, E. G. Manoilov1, E. V. Begun1, O. M. Sreseli2, and I. I. Geru3 1V Lashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv 03028, Ukraine 2Ioffe Physical-Technical Institute of the Russian Academy of Sciences, St.-Petersburg 199034, Russia 3Institute of Chemistry of the Academy of Sciences of Moldova, Chisinau, MD-2028, Moldova

The effect of microwave radiation on the transformation of impurity-based structural complexes in CdTe:Cl single crystals is studied using low-temperature photoluminescence measurements. It is shown that microwave radiation activates ClTe centers, resulting in an increase in the intensity of photoluminescence line of excitons bound at the corresponding ClTe donor centers. A nonmonotonic dependence of the integrated photoluminescence intensity on the duration of microwave irradiation is observed. At the initial stage of microwave irradiation (t = 30 s), an increase in the integrated excitonic photoluminescence intensity is observed; as the duration of microwave irradiation is increased, the photoluminescence intensity decreases. The experimentally observed variations in the photoluminescence intensity are athermal in nature. The hypothetical mechanism of transformation of impurity-based structural complexes is described.

An analysis of physical mechanisms responsible for the influence of stabilizer type and ambient material on CdTe nanocrystal growth rate and passivation effectiveness of surface dangling bonds has been carried out. The possibility to change properties of nanocrystals by changing the stabilizer type has been shown.

The technology for preparing colloidal CdTe quantum dots (QDs) in an alcaline medium in the presence of passivators thioglycolic acid (TGA) and L-cysteine (L-cys) as well as the technology for preparing colloidal CdSe QDs by method of the reverse micelles is presented. The CdTe QDs were synthesized at different technologic conditions in an aqua colloidal solutions as well as in a polymeric matrix of poly(diallydimethylammonium chloride). For synthesis of CdSe QDs in microemulsion system Triton X-100 and n-hexyl alcohol were used. Cyclohexane served as a non-polar phase, water and water solutions of cadmium acetate and sodium selenide were used as polar phase. The peculiarities of photoluminescence (PL) and optical absorption spectra of CdTe QDs in the 4.2 K– 300 K temperature range were investigated. PL spectrum consist of relatively narrow exciton line with maximum at 2.1–2.4 eV for QDs synthesized at different content of thioglycolic acid (TGA) and L-cysteine (L-cys). It was shown that the Stokes shift in PL and optical absorption spectra monotonically increases from 170 meV to 200 meV at decreasing of QDs size from 3.1 nm to 1.8 nm that is caused by the increasing of the electron–phonon interaction. The dependence of the Huang-Rhys factor on QDs size was obtained.

This paper deals with the theoretical and experimental study of radiative processes in zero-dimensional Si and Ge nanostructures consisting of a system of Si or Ge nanocrystals embedded in an Al2O3 matrix. The Al2O3 films containing Si or Ge quantum dots were produced by pulsed laser-assisted deposition. The timeresolved photoluminescence spectra of the films were recorded in the energy range from 1.4 to 3.2 eV in the range of photoluminescence relaxation times between 50 ns and 20 μs. The exciton binding energy and the energy of radiative excitonic transitions are calculated, taking into account the finite barrier height and the polarization of heterointerfaces. In addition, the excitonic photoluminescence spectra are calculated, taking into account the effect of quantum mesoscopic fluctuations and the possible nonmonotonically varying dependence of the radiative zero-phonon lifetime of excitons on the dimensions of the quantum dots. The observed agreement between the calculated and recorded photoluminescence spectra confirms the excitonic nature of photoluminescence and provides a means for the determination of the model parameters of photoluminescence in the nanostructures.

The exciton binding energy and the energies of radiative excitonic transitions in the separate SiOx-Si-SiOx quantum wells are calculated in the effective-mass approximation with the quadratic dispersion relation. Along with the real finite offsets of the bands in such quantum well structures, the effect of dielectric enhancement of the exciton binding energy due polarization of the heterointerfaces is taken into account. In addition, the dependence of the zero-phonon radiative excitonic recombination time on the width of the SiOx-Si-SiOx quantum well is calculated. This dependence exhibits unsteady (oscillating) behavior, which is caused by the indirect band gap of the silicon material. It is shown that the theoretically calculated energies of the radiative excitonic transitions in the SiO2-Si-SiO2 quantum wells match the experimentally determined energies for the quantum wells whose widths are larger than 1.5 nm. Good agreement between the theoretically calculated and experimental spectral dependences of photoluminescence in the SiO2-Si-SiO2 quantum wells is attained.

Variations in absorption and emission spectra induced by thermal treatment are reported for aqueous solutions of thiol-stabilized CdTe nanocrystals with different Cd2+:Te2– molar ratios. Heating of colloids was shown to result in appearance of two photoluminescence lines that were assigned to two ensembles of nanocrystals with different mean diameters. Effect of heat treatment on size distribution, absorption and emission properties, and stability of nanocrystals with various Cd2+:Te2– molar ratios is discussed in the terms of different coverage of the nanocrystal surfaces with tellurium atoms (ions?) and with thioglycolic acid molecules. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An original iterative procedure has been developed to obtain energy spectrum of neutral and charged excitons (positive and negative trions) in spherical semiconductor quantum dots (QD) imbedded into a dielectric material. Numerical calculations are made using the effective mass approximation and Hartree-Fock method. A combined effect of heterointerface polarization (image force potential) and finite band-off-sets on the energy spectrum of excitons and trions in QDs is considered for the first time. It is shown that binding energies of excitons and trions in such QDs can be substantially larger than those in bulk semiconductors due to spatial and "dielectric" confinement effects.

The CdTe:Si single crystals with Si concentration in the range of C{sub Si}{sup 0}=2x10{sup 18}-5x10{sup 19} cm{sup -3} are grown by the Bridgman-Stockbarger method. The samples were of the n-and p-type with electrical conductivity {sigma}=2x10{sup -1}-8x10{sup -9} {omega}{sup -1} cm{sup -1}. Being heated in the temperature range 300-440 K, the p-CdTe crystals were annealed, and their conductivity decreased. The shape of the low-temperature (5-20 K) photoluminescence spectra of the samples are indicative of their high structural quality. The specific feature of the emission of the CdTe:Si crystals is its decrease in the intensity of all lines induced by donors as the samples are cut progressively closer to the ingot top. The results obtained indicate that the Si impurity, in contrast with Ge, Sn, and Pb, does not exhibit the compensating and stabilizing effect in CdTe.

The exciton binding energy, the energies of the basic radiative exciton transition, and the zerophonon radiative lifetime of excitons in silicon quantum dots embedded in the SiOx matrix are calculated in effective mass approximation with quadratic dispersion relation. In addition, the spectra of steady-state photoluminescence and of time-resolved photoluminescence of excitons in the silicon quantum dots are calculated, and the kinetics of the photoluminescence relaxation is considered. The theory is compared with the experiment. It is shown that, for nanostructures involving silicon quantum dots with diameters smaller than 4 nm, the governing factor in the broadening of the spectral photoluminescence bands is the effect of mesoscopic quantum fluctuations. In this case, either an even one dangling bond at the interface, or one intrinsic point defect, or one foreign atom located inside the small-sized nanocrystallite or in its close surroundings produces a pronounced effect on the energy of the exciton transition.

Photoluminescence spectra of CdTe:Cl crystals were measured at 5 K before and after irradiation by the second harmonic of a YAG:Nd laser. It was found that the Huang–Rhys factor for donor–acceptor pair (DAP) recombination increases after irradiation with laser power above the CdTe melting point which is explained by a decrease of the DAP concentration due to Cd evaporation and to the presence of the thermogradient effect.

The evolution of photoluminescence (PL) spectra with increasing γ-irradiation dose was monitored for undoped and Cl-doped CdTe crystals. The emission intensities and the Huang-Rhys factors for different PL lines were determined as a function of the exposure dose. In irradiated CdTe:Cl, an irradiation-induced enhancement of the electron-phonon coupling for the A-center PL was attributed to decreasing concentration of the donor–acceptor pairs responsible for this band. Gamma-irradiation of undoped CdTe at a dose larger than 10 kGy resulted in quenching of the A-center PL at 1.4 eV, the donor–acceptor line in the edge luminescence at 1.55 eV, as well as emission of the donor-bound excitons. Observed peculiarities are explained by a decrease of concentration of isolated donors, presumably through the creation of complexes with intrinsic defects generated by γ-rays.

The dependence of carrier density in silicon quantum wires sheathed with SiO2 on the wire diameter and the position of impurity atoms in respect to the wire center is analyzed theoretically. It is shown that, as the diameter of wires and nanocrystals decreases, the ionization energy of a dopant increases; therefore, the free carrier density decreases, and the screening of the Coulomb attraction becomes ineffective. As a result, the photoluminescence is defined by the radiative recombination of excitons even in the case of heavily doped Si. These conclusions are supported by the data of experimental study of spectral, excitation-power, and temperature dependences of photoluminescence in porous silicon structures fabricated on lightly and heavily doped Si substrates.

Obtained experimental data on low-temperature photoluminescence are used to numerically simulate the energy states in symmetrical and asymmetrical short-period (GaAs)N/(AlAs)M superlattices with the (001) orientation. The matrix formalism in the envelope-function method is employed to study trends in the behavior of the miniband spectrum in models with different boundary conditions. It is shown that correct information about the type of transitions in the materials under consideration can be obtained even if the boundary conditions are diagonal. The effect of corrections on the miniband spectrum that arise when mixing of the states belonging to the Γ and X valleys is taken into account and a δ-functional potential localized at the heterointerface is present is studied.

High-resolution x-ray diffraction and photoluminescence experiments were carried out on short-period direct-gap GaAs/AlAs superlattices. Despite a small difference in the well and barrier thicknesses of the samples studied, both the deformation of superlattice (SL) layers caused by the lattice mismatch and thermal activation energy of non-radiative recombination were found to differ for the different samples. The correlation observed between the deformation reduction and the activation energy increase as the SL period decreases is discussed in the context of a configuration coordinate diagram.

The effect of surface treatments on the main characteristics of excitons in the subsurface region of semiconductors (for GaAs), as well as the spatial distribution of main characteristics of excitons (for CdS), was studied. An analysis of experimental data showed that the deposition of insulator layers with a lower dielectric constant on the surface of the semiconductor resulted in an enhancement of the exciton-phonon interaction and an increase in the exciton binding energy. The appearance of the surface layer with a higher defect concentration increasing after some surface treatments results in the lowering of the exciton binding energy in the subsurface region and also in the weakening of the exciton-phonon interaction.

Ultrashort-period GaAs/AlAs superlattices of type-II were investigated by low-temperature photoluminescence spectroscopy. The photoluminescence spectra consisting of many lines were carefully analyzed to obtain energy position, full width at half maximum and relative intensity for each individual line. Influence of the energy band structure, layer thickness and interface disorder on the radiative electron-hole transitions in these structures is discussed.

The interaction of electrons and phonons is strongly enhanced in ultrashort-period GaAs/AlAs superlattices. The enhancement is caused by an increase of the exciton binding energy with decreasing superlattice period. The photoluminescence spectra of indirect-gap superlattices exhibit a zero-phonon line due to scattering by defects and/or interfacial roughness as well as pronounced phonon sidebands.

Characteristics of GaAs/In$_{x}$Ga$_{1-x}$As/GaAs heterostructures with a single quantum well, which were obtained at various growth parameters, are evaluated according to the results of measurements of low-temperature photoluminescence spectra and their corresponding theoretical analysis., Comment: 8 pages, 5 figures

Nonsymmetric short-period GaAs/AlAs superlattices, for which the well thickness is at least a factor of 2 larger than the barrier thickness, have been shown to exhibit a direct band gap for any well thickness. These superlattices are characterized by an enhanced intensity of the luminescence as compared to their symmetric indirect-gap counterparts with the same well width, and, thus, may be used as light-emitting devices, in particular, as low-threshold lasers in the red visible spectrum. This conjecture is supported by the observation of stimulated emission at T=80 K for a GaAs/AlAs superlattice with six monolayers well and three monolayers barrier width.

We present the tensoresistivity effects which demonstrate the pressure‐induced increase of the mobility of electrons and holes at certain orientations of uniaxial pressure X with reference to the [100] crystallographic axis. The uniaxially strained channels occur in silicon n‐MOS‐transistors and p‐MOS transistors [1, 2]. Both longitudinal tensoresistivity (TR) and transverse TR investigation in high uniaxially strained n‐Si(P) and p‐Si(B) are presented.. In n‐Si the change of the longitudinal TR and transverse TR at X ‖ [100] is determined by both the change of f‐transition probability with increasing pressure and the redistribution of electrons between the valleys with the effective mass m‖ (longitudinal TR) and m⊥ (transverse TR). It is shown that the strong anisotropy of longitudinal TR and transverse TR are caused by pressure‐induced change of isoenergetic surface shape, i.e. by the change of heavy holes effective mass and its anisotropy.

Experimental data were found to be in qualitative agreement with theoretical calculations of the degree of linear polarization. The effect of the pumping level on the shape of photoluminescence spectra of superlattices with various types of bands was established. The electron-phonon coupling constants of type-II superlattices were evaluated.

The transition from an indirect to a direct energy band structure has been induced in short-period GaAs/AlAs superlattices by going from a symmetric to an asymmetric distribution of the well and the barrier thickness within the unit cell of the superlattice. Reducing the barrier thickness dB to half the well thickness dW moves the lowest state in the conduction band from the X point in the AlAs barrier to the Γ point in the GaAs well. For dW=2dB, the band structure becomes therefore direct for all values of dW. This change in the type of energy gap is accompanied by a significant enhancement of the integrated photoluminescence intensity for asymmetric superlattices.

An investigation was made of the processes taking place in gallium phosphide light-emitting diodes exposed to ultrasound treatment. It was observed that the luminescence intensity of the diodes decreases monotonically in the field of an ultrasound wave. After the action of the ultrasound has ceased, the radiative recombination intensity gradually recovers. The degradation effects occur as a result of the destructive effect of the ultrasound on bound excitons and the formation of nonequilibrium dislocation pileups at room temperature.

The polarization dependence of the photoluminescence of GaAs-AlAs superlattices with different well and barrier widths has been investigated. In wide-well superlattices (10-15 nm) the luminescence signal of free excitons has the largest degree of polarization (20-25%). In short-period superlattices, however, the recombination is dominated by indirect, localized excitons (X- Gamma ), which are exposed to anisotropic perturbations along the (110) crystallographic axis. This results in an anomalous detection angle dependence of the polarization.

We have studied, both theoretically and experimentally, the mechanism of photoluminescence (PL) of Ge nanocrystals in SiO2 and GeO2 matrices. Ge quantum dots (QDs) have been created by pulsed laser deposition (PLD). Time-resolved PL spectra in the photon energy range of 1.4– 3.2 eV have been measured within the time range 50 ns–20 µs. We have calculated the exciton binding and radiative transition energies accounting for both finite potential barriers and heterointerface polarization in the system. PL spectra have been calculated and compared with experimental results accounting for quantum-mesoscopic fluctuations and possible oscillations in exciton radiative lifetime occurring as QD size decreases. Good agreement between calculated and experimental PL spectra supports an assumption on the excitonic character of PL in Ge QDs and enables the parameters of the PL model to be determined.

An experimental and theoretical study is made of the reflection spectra of surface excitons and exciton–impurity complexes. The conditions for the localization of the excitons near the CdS surface are fulfilled experimentally by low-energy argon ion bombardment (E ⪅ 1 keV). The binding energy of the surface excitons at impurities of small effective charges is calculated theoretically. It is shown that the binding of the surface excitons at an impurity center is possible both, for positive and negative effective charges. Satisfactory agreement is observed between the theoretical calculation of the reflection spectrum within the frequency range of the surface excitons and the experimental data for Ar-ion bombarded CdS surface. [Russian Text Ignored].

It has been shown that band parameters for unimplanted films differ from those for bulk materials. Mechanical stresses and increased concentrations of defects seem to be responsible for this difference. The neighbourhood of the surface and the existence of drain paths for bulk defects determine the activity of the surface as a collector for mobile defects and hence their accumulation and their subsequent combination and annihilation reactions. From this point of view ion-implanted films with radiation-induced defects exhibit specific types of behaviour. For example, low energy ion bombardment (together with the removal of a very thin surface layer by etching) leads to an extensive movement of defects towards the surface and to a purification of the corresponding layer. In a number of cases even structural phase transformations take place within the surface layer, which lead in particular to the creation of surface excitons. High energy ion bombardment does not alter the band parameters of the films at the depth d of ion penetration but distorts the structure at the surface owing to a drain of defects into this layer. At the same time centres of scattering and radiative recombination are effectively induced at the depth d.

The spectral and planar distribution of the luminescence intensity of the electron-hole plasma (EHP) created by laser excitation in the subsurface region of a direct-band semiconductor like GaAs in contact with a dielectric medium (Si3N4) is studied. High optical excitation levels (L ≈ ≈ 5 MW/cm2) make possible to detect: (1) the appearance of stimulated radiation mainly from the regions of the sample edges; (2) the expansion of EHP from the excited region predominantly along the GaAs-Si3N4 interface up to a distance (l ≈ 50 to 100 μm), which is several times greater than the corresponding bulk value. The assumption is made that the electron-hole liquid is created not only at the “tails” of the expanded plasma, but also within the excited regions (in the latter case after a partial cooling of EHP, when in the process of the relaxation the electron-hole pairs concentration achieves the EHP-condensation value n ≈ 1016 cm−3). The mechanism of a long-wave range tail formation in EHL radiation, which is caused by the energy losses on non-equilibrium plasmons, is discussed. [Russian Text Ignored]