Abstract. 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 (14H 1 4334, 10H 2 55, 14H 2 77). 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.
Temperature dependence of magnetic switching processes with multiple jumps in Fe/MgO (001) films is investigated by magnetoresistance measurements. When the temperature decreases from 300 K to 80 K, the measured three-jump hysteresis loops turn into two-jump loops. The temperature dependence of the fourfold in-plane magnetic anisotropy constant K 1 , domain wall pinning energy, and an additional uniaxial magnetic anisotropy constant K U are responsible for this transformation. The strengths of K 1 and domain wall pinning energy increase with decreasing temperature, but K U remains unchanged. Moreover, magnetization reversal mechanisms, with either two successive or two separate 90 • domain wall propagation, are introduced to explain the multi-jump magnetic switching process in epitaxial Fe/MgO(001) films at different temperatures.
Abstract. In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown original defects are reported. , N D 110 18 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 DL i (i = 1, 2, 3, 4) spectra. The appearance of the DL i spectrum is associated with formation of new nano-phases. Data of photoluminescence, excitation and absorption spectra show the uniformity of different DL i spectra. Structurally, the general complexity of the DL i 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 (SF i ) spectra. The DL i spectra differ from SF i spectra and have other principles of construction and behavior. The DL i 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 DL i and SF i spectra coincide and indicate formation of nanostructures 14H 1 4334, 10H 2 55, 14H 2 77, 8H44.
Abstract. 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 (E gx ) 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.
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.
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