The dependence of photoluminescence spectra of SiGe/Si(001) structures with self-assembled islands on Ge deposition temperature was investigated. Due to inhibition of SiGe alloying and an increase of the Ge content in islands the photoluminescence peak from the islands significantly shifted to low energy with a lowering temperature. The maximum of the peak from the island grown at 600°C was observed at energies less than the energy of the bandgap for bulk Ge. As a result of holes localization in islands the photoluminescence peak from the islands was observed up to room temperature. Sufficient enhancement of the room-temperature intensity of the photoluminescence signal at 1.55 μm was obtained for structures with islands grown on pre-deposited Si1-xGex layer. It is associated with a more effective capturing of holes by densely packed islands in structures with a pre-deposited Si1-xGex layer.
The intensive up-conversion photoluminescence (UPL) was observed at low temperatures in CdSe/ZnSe structures with single CdSe inserts of a nominal thickness of 1.5 and 0.6 ML. The quadratic-like dependence of UPL intensity on the excitation power was obtained. UPL mechanism was interpreted on the basis of non-linear process of two-step two-photon absorption (TS-TPA) through deep defect states including cation vacancies localized at the barier-nanoisland heterointerface.
Pseudomorphic strained-layer AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures have been studied by means of photoluminescence (PL) and Raman scattering. It is established the correlation between the PL line shape changes and the Raman spectra modification when the QW width is below the critical layer thickness (CLT) estimated to be of 25 nm for y = 0.1. The PL feature observed for the InGaAs QW width equal to 20 nm as extremely narrow exciton-like peak with the FWHM equal 1.5 meV at low temperature (T = 6K) transforms into broad band of the FWHM equal 16 meV when the QW width reaches the value about of 12 nm. The PL line shape broadening is accompanied by the modifications of Raman spectra. A new line arising at the spectral position v = 160 cm-1 is assigned to impurity-induced longitudinal acoustic optical mode of InyGa1-yAs. The changes observed in optical spectra are related to generation of defects in the under-CLT region.
Comparative study of nitrogen implanted a-C:H film has been carried out by micro-Raman and nanoindentation techniques. At high dose nitrogen implantation (1(DOT)1017 cm-2) the structural inhomogeneities are observed in the implanted region. After implantation a significant broadening and energy shift of both G- and D-bands in Raman spectra are observed. On the other hand, film hardness measurements reveal the existence of more dramatic differences between both implanted regions with homogeneous and structural inhomogeneities. The film hardness in the inhomogeneous region more than by 5 times exceed the one in the homogeneous region. The hardness improvement of ion implanted a-C:H film is related to film disordering and ion beam induced phase-structure transformation in the implanted region.
Si/SiO2 structures implanted by Si+ ions are investigated with photoluminescence (PL), electron spin resonance and low frequency Raman scattering (RS) methods. The nature of the PL band at 2.0 eV that appears after implantation is identified. The sizes of Si nanocrystals formed after the implantation and thermal annealing at T equals 1200 degree(s)C are determined by low frequency RS method. It is shown that low temperature plasma treatment of the annealed samples leads to the increase of PL intensity.
Hydrogenated amorphous diamond-like carbon (DLC) films produced by RF-glow discharge deposition from hydrocarbon mixtures in a parallel diode-type plasma reactor were investigated. The DLC films were obtained at various gas mixture compositions and bias voltages (Vb). Raman spectra of DLC films in the range 1000 - 1800 cm-1 were analyzed. Our results are given in terms of I(D)/I(G) intensity ratio, bands position, and width (FWHM) as a function of bias voltage and gas mixture. The analysis of Raman spectra shows that bias voltage value is critical for the DLC films structure. The increase of Vb from -200 V to -700 V results in the essential high-frequency shift of G- and D-bands and change of their intensities ratio I(D)/I(G) from 0.64 (Vb equals 200 V) to 3.2 (Vb equals 700 V). Similar high-frequency shift, change of FWHM and I(D)/I(G) intensities ratio were observed at the variation of methane concentration in gas mixture composition from 100 to 20%.
The results of light scattering and photoluminescence investigations of sub micron free- standing silicon crystals are presented. Measurements were carried out within the wavelength range 0.2 - 1.5 micrometer. It was found that if the size of micro crystals is less than 1 micrometer, the peak of (L3 - L'3)-transition in the absorption spectrum shifts towards larger photon energies. We have found also that the micro crystals are the strongly depolarizing medium, and the depolarization depends on wavelength and angle of observation. Moreover, s- and p-polarized scattered light spectral dependences are different. The photoluminescence spectra of the crystals of micron and submicron scale are essentially different from the conventional bulk silicon spectra. At 4.2 K temperature we have observed new visible and several infra-red photoluminescence bands. While at room temperature only visible light band was found. The results obtained are treated using the Mie's theory and the suggestion of the surface atomic layers reconstruction.
Photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR) have been used to characterize porous silicon layers (PSL) exposed to HF destructive etching. The results obtained lend support to the view that chemical passivation, in particular by oxygen, is the major factor which controls the origin of PL. The PL intensity and the PL shift are ascribed to the changes in hydrogen and oxygen termination of pores.
MicroRaman, Raman, photoluminescence and x-ray diffraction spectra were measured for different SiC splices. It has been shown that Raman and especially MicroRaman scattering gives us a gain over other diagnostic techniques on the way to define polytype structure of the splice.
New concepts are developed to describe a wide area of nonlinear systems involving the phase relaxation peculiarities for the degenerate two-level system under the resonant optical excitation. Nonlinear susceptibility of the two-level system becomes anisotropic, and self-induced changes of polarization (SICP) are developed to the large (gigantic) magnitudes. The nonlinearities of two different natures are considered: the saturation of absorption and the resonant optical reorientation of anisotropic defects. For these particular cases, the SICP effects manifest themselves at a field much lower than that in traditional nonlinear optics. The larger magnitudes of the effects offer good possibilities for the development of optical devices based on the new physical principles. Various applications of SlOP effects are demonstrated, including the spectroscopic investigations of impure cubic crystals, optical diagnostics, optical storage, information processing, and the development of new optical devices.
Photoluminescence investigations of silicon subjected to such industrial treatments as implantation, high temperature postimplantation annealing, treatment in high frequency discharge plasma, as well as the prolonged thermal annealing with the formation of thermal donors were carried out. It was shown that photoluminescence can be used for direct observation of the implanted impurity activation under various postimplantation treatments. Photoluminescence also proved to be useful for indirect control of thermal donors generation in Si:Ge.
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