Nanocrystalline silicon carbide films for solar cells

Nanocrystalline silicon carbide (nc-SiC) films as protective coating and as solar cell material for a harsh environment, high temperatures, light intensities and radiation, were investigated. p- and n-types 100-mm silicon wafers with (100) orientation were used as substrates for SiC films deposition. The films were deposited using HighFrequency Plasma Enhanced Chemical Vapor Deposition (HF-PECVD) with CH₃SiCl₃ gas as a silicon and carbon source. Hydrogen supplied CH₃SiCl₃ molecules in the field of HF discharge. Deposition was carried out on a cold substrate. The power density was 12.7 W/cm². Deposition conditions were explored to prepare films with a controlled band gap and a low defect density. Formation of nc-3C-SiC films has been confirmed by the high resolution-transmission electron microscopy analysis, optical band gap values ETauc, conductivity, charge carrier activation energy and Hall measurements. The efficiency of photoconductivity was calculated for evaluating the photoconductivity properties and for the correlations with technology. For p-n junction creation in solar cell fabrication, the ntypes nc-SiC films were doped with Al. Employing Al as a doping material of nc-n-SiC, the open-circuit voltage as high as 1.43 V has been achieved

Peculiarities of phase transformations in SiC crystals and thin films with in-grown original defects

Phase transformations of SiC crystals and thin films with in-grown original defects have been studied. The analysis of absorption, excitation and low-temperature photoluminescence spectra testifies to formation of new micro-phases during the growth. The complex spectra can be decomposed into similar structure-constituting spectra shifted against each other on the energy scale. These spectra are indicative of formation of new nanophases. Taking into account the position of the short-wave edge in the zerophonon part of the SF-i spectra as well as the position of corresponding excitation spectra and placing them on the well-known linear dependence of the exciton gap (Egx) on the percentage of hexagonally in different polytypic structures, one can obtain a hint to the percentage of hexagonally in the new metastable structures appearing in the 6H (33) matrix or in the growth process. The SF spectra are indicative of the appearance of these metastable structures

White Light Emission of ZnO-Cu Nano-Films

The ZnO films were prepared by reactive rf-magnetron sputtering on silicon and sapphire substrates. For Cu-doping of the ZnO films, the close space sublimation method (CSS) was used at atmospheric pressure in air. After CSS processing, the ZnO and ZnO-Cu films were annealed in a wet media. The reference ZnO-Cu films, obtained from ZnO-Cu target by electron-beam evaporation (EBE) were treated at the same conditions. The microstructure and optical properties of the samples were compared and studied by atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence (PL) and cathodoluminescence (CL) spectra. XRD results indicated that all the ZnO films have a polycrystalline hexagonal structure. The surface and crystal quality of ZnO thin film was improved when doped with Cu. The shape of the spectrum depends on the method of doping. Spectrum of the reference ZnO-Cu films has green band only. Spectrum of ZnO-Cu films consists of three emission bands at doping by CSS. The first band is in a blue region with a maximum at 465 nm. The second and third bands are in the green and orange regions with maximum at 520 and 580-600 nm, respectively. The green band is the most intensive. As a consequence, the emission looks like white light. Origin of observed emission bands is discussed

Измерение эстрогенов в тканях молочной железы методом жидкостной хроматографии и тандемной масс-спектрометрии

Although estrogen contribution estrogen to breast cancer development is not fully understood, an effective method of their measurement, in the mammary gland might provide additional insight. In this study, we have developed a LC-MS/MS method of simultaneous quantification of estrone and estradiol in breast tissue samples. Analytes were extracted with methyl tert-butyl ether by sonication and derivatized with dansyl chloride. Estrogens were analyzed by liquid chromatography-tandem mass spectrometry with an electrospray ionization source. Accuracy and precision were better than 20% for most concentrations. Although estrone and estradiol levels in normal and malignant breast tissue samples analyzed using our method insignificantly differed. The method developed may be used in further studies aimed at evaluating a role estrogens in breast cancer risk.Воздействие эстрогенов считается одним из основных факторов риска развития рака молочной железы, однако механизмы действия этого фактора до конца не изучены. В связи с этим актуальным является создание методов оценки содержания эстрогенов в тканях молочной железы. В данной работе представлены результаты разработки метода количественного определения эстрона и эстрадиола в образцах ткани молочной железы с помощью высокоэффективной жидкостной хроматографии с масс-спектрометрической детекцией. Аналиты экстрагировали метил-трет-бутиловым эфиром в ультразвуковой бане и дериватизировали дансилхлоридом. Были рассмотрены варианты нормировки количественных данных на исходную массу ткани и на массу экстрагированных липидов. Точность и прецизионность конечного метода были выше 20% для большинства концентраций. С помощью метода были проанализированы уровни эстрона и эстрадиола в образцах нормальной и злокачественной ткани молочной железы. Разработанный метод может быть использован в дальнейших исследованиях влияния эстрогена на риск развития рака молочной железы

8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions

In this paper the results of photoluminescence researches devoted to phase transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by Tairov’s method with and without polytype joint before and after plastic deformation at high temperature annealing were investigated using optical spectroscopy. Low temperature photoluminescence changes in the transition phase of SiC crystal represented with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking fault spectra indicate formation of metastable nanostructures in SiC crystals (14H₁ , 10H₂ , 14H₂ ). The phononless part of each stalking fault spectrum consists of two components of radiative recombination that are responsible for hexagonal and cubic arrangement of atoms. Each of radiative recombination components in the stalking fault spectrum has the width of entire band 34 meV and shifts relative to each other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine structure of the recombination components in spectrum is observed, and it is related to different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is similar (temperature, decay of luminescence). The processes of the phase transition are explained by the mechanism of interfacial rearrangements in the SiC crystals

3C-6H transformation in heated cubic silicon carbide 3C-SiC

Results of the research on the photoluminescence study of the 3C-6H-SiC phase transformation are presented. 3C-SiC crystals with in grown 3C-6H transformation and pure perfect 3C-SiC crystals grown by the Tairov-Tsvetkov method without a polytypes joint after high temperature annealing were investigated. Fine structure at the energy of E = 2.73, 2.79 eV, E = 2.588 eV, and E = 2.48 eV that appeared after annealing was described. The role of stacking faults in the process of structure transformation was investigated

Structure of photoluminescence DL-spectra and phase transformation in lightly doped SiC crystals and films

In this work, the results of investigations of DLi spectra in α-SiC crystals and films with a low impurity concentration have been presented. Photoluminescence spectra of lightly doped SiC single crystals and films with the impurity concentration of ND–NA ~ (2…8)∙10¹⁶ cm⁻³, ND ~ (5…8)∙10¹⁷ cm⁻³, and ND–NA >3∙10¹⁷ cm⁻³, ND ≥ 1∙10¹⁸ cm⁻³ (NDLsamples) were investigated within the temperature range 4.2…77 K. Complex spectroscopic study of one-dimensional disordered structures caused by solid phase transformations in SiC crystals was presented. Disordered growth D-layers in lightly doped crystals and α-SiC films were investigated using low temperature photoluminescence. The analysis testifies that DL and SF spectra hand-in-hand follow the structure transformations. It has been shown that the DL and SF spectra of luminescence reflect the fundamental logic of SiC polytypes structure. This allows to observe the structure changes at the phase transformations, the growth of SiC polytypes and to control their aggregates

Nanostructures in lightly doped silicon carbide crystals with polytypic defects

In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown original defects are reported. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)*10¹⁶ cm⁻³, NA ~ (2…8)*10¹⁷ cm⁻³, and ND – NA ~ (1…5)*10¹⁷ cm⁻³, ND = 10¹⁸ cm⁻³ were investigated. The analysis of absorption, excitation and low temperature photoluminescence spectra suggests formation of a new micro-phase during the growth process and appearance of the deep-level (DL) spectra. The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2, 3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new nano-phases. Data of photoluminescence, excitation and absorption spectra show the uniformity of different DLi spectra. Structurally, the general complexity of the DLi spectra correlated with the degree of disorder of the crystal and was connected with onedimensional disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi spectra differ from SFi spectra and have other principles of construction and behavior. The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals with higher concentrations of non-compensated impurities. The excitation spectra for the DLi and SFi spectra coincide and indicate formation of nanostructures 14H₁, 10H₂, 14H₂, 8H<44

Peculiarities of photoluminescence spectra behavior in SiC crystals and films during phase transformations

Peculiarities of photoluminescence spectra behavior in SiC crystals and thin films with in-grown defects during phase transformations have been studied. On the deep-level(DL)-spectra, as an example, their characteristics and behavior were investigated. It has been shown that all DL spectra have the same logic of construction and demonstrate identical behavior of the thin structure elements

External impacts on SiC nanostructures in pure and lightly doped silicon carbide crystals

Influence of plastic deformation and high-temperature annealing (T = 2100 °C, t = 1 h) on SiC crystals with grown polytypic junctions demonstrating SF and DL spectra have been presented. SF-i and DL-i type luminescence are inherent to SiC crystals with distortions of the structure related with availability of packing defects that lead to onedimensional disordering (along the c-axis). They are a most expressed in doped crystals with original growth defects. DL luminescence appears in pure crystals at plastic deformation and in doped crystals at a hydrostatic pressure. It enhances at the high temperature annealing, too