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[en] Metastability of states associated with point defects in semiconductors in an interesting fundamental property turning out to be more common than erstwhile. This article highlights two important examples of metastable defects, one in the elemental semiconductor silicon and the other in the compound semiconductor Zn Se, of significant current interest for blue-emitting devices. (author)
[en] The electronic structure of zinc chalcogenide crystals doped with nontransition V elements was studied in the cluster approximation on the basis of a physically adequate method accounting for boundary conditions. It is shown that the formation of A-centers is a specific manifestation of a general tendency toward the reconstruction (relaxation) of impurity centers, which is mainly caused by the change in crystal electronic structure upon doping. Specific features of the formation of reconstructed centers with different charge states are studied for a series of impurities and crystalline matrices. 19 refs., 3 tabs
[en] It is suggested that the existing classification of polytype structures of zinc sulfide be supplemented with an additional criterion: the characteristic of regular point systems (Wyckoff positions) including their type, number, and multiplicity. The consideration of the Wyckoff positions allowed the establishment of construction principles of known polytype series of different symmetries and the systematization (for the first time) of the polytypes with the same number of differently packed layers. the classification suggested for polytype structures of zinc sulfide is compact and provides a basis for creating search systems. The classification table obtained can also be used for numerous silicon carbide polytypes. 8 refs., 4 tabs
[en] ZnS polytypes are formed by martensitic transformations from their common parent, the hexagonal 2H structure, and their crystallographic characteristics depend on the detailed transformation mechanism. The ratio of the number of rhombohedral to the number of non-rhombohedral polytypes in the population of the currently identified polytypes is 1.5. It was formerly argued that the expected ratio is 2 and that the discrepancy indicates that the population is biased. An analysis based on the established properties of martensitic transformations in ZnS shows that the ratio of rhombohedral to non-rhombohedral polytypes depends on the transformation probability by a dislocation dipole; it is further shown that the experimental ratio of 1.5 can be derived by assuming the plausible value of 0.8±0.1 for this probability. (orig.)
[en] We investigated the properties of artificial pinning centers of YBCO multilayer films in which Y2O3 and ZnO nanoparticles are uniformly introduced by using the pulsed laser deposition (PLD) technique. Y2O3 and ZnO nanoparticles were deposited on top of YBCO buffer layer and the density of nanoparticles was controlled by varying the number of nanoparticle layers. YBCO superconducting layers with total thickness of 250 nm were deposited on top of Y2O3 and ZnO nanoparticles. Based on analyses of the surface morphology, the transition temperature Tc, and the critical current density Jc, we discussed the difference between the two kinds of nanoparticles as flux pinning centers.
[en] A triple-color photodetector with MSM structure based on the ZnO/MgZnO films was fabricated. There are three response peaks in the response spectrum for the triple-color photodetector, which response peaks are located at around 290, 320 and 360 nm, respectively. A further study on responsivity for the triple-photodetector is carried out. The rising velocity of cubic MgZnO (111) response peak is faster than hexagonal MgZnO (002) response peak, the different internal gain between the different crystal orientation is the main reason for the different of the response peaks between the two phases. This experiment would have a great significance for multiple-colors photodetectors field.
[en] We demonstrate the formation of self-assembled homogenous flower-like ZnO nanorods over a ZnO seed layer deposited on a HF-etched Si (111) substrate. The typical flower-like morphology of ZnO nanorod arrays is ascribed to the formation of the island-like seed layer which is deposited by the drop method followed by annealing at 300 °C. The island-like ZnO seed layer consists of larger ZnO grains, and is built by constraining of the Si (111) surface due to pattern matching. Pattern matching of Si with ZnO determines the shape and size of the seed layer and this controls the final morphology of ZnO nanorods to be either flower like or vertically aligned. The high quality of the island-like ZnO seed layer enhances the diameter and length of ZnO nanorods. Besides, while the amorphous layer formed during the annealing process would influence the strained ZnO grain, that subsequent amorphous layer will not block the constraining between the ZnO grain and the substrate. (paper)
[en] Highlights: • Conduction band offsets of Zn1-xMgxSe/Zn1-yMgySe heterointerfaces. • Valence band offsets of Zn1-xMgxSe/Zn1-yMgySe heterointerfaces. • Relaxed and strained band-gap energies for various compositions y. • The present investigation could provide valuable support in the design of Zn1-xMgxSe based heterostructures for future device applications. - Abstract: Based on the model-solid theory coupled with a pseudopotential approach within the virtual crystal approximation, the conduction and valence band offsets (CBO) and (VBO) of the unstrained and strained Zn1-xMgxSe/Zn1-yMgySe heterointerfaces have been investigated. The calculated elastic constants C11 and C12 for ZnSe and MgSe are found to agree to within 7% with experiment. Our findings showed that for electrons the CBO is negative whereas the Mg content of the overlayer (x) is lower than the Mg content of the substrate (y). Nevertheless, the reverse can be seen when x > y. As regards the light-and heavy holes the VBOs remain negative as far as the Mg concentration of the overlayer is lower than that of substrate layers and become positive in the opposite case. The alignment of the bands is found to be of type II (staggered) whatever is the Mg compositions of both the overlayer and the substrate layer. The relaxed and strained band-gap energies versus the composition y have been computed and the results are examined and discussed.