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[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.
[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 sound generated from a periodically illuminated solid as a photoacoustic effects first discovered in 1881 is used to investigate the properties of materials. The PA spectra of ZnTe and ZnSe crystal were obtained by PAS method. The absorption spectrum of materials which is not accesible with optical spectroscopy can be obtained by PA spectroscopy. The PA signals were proportional to absorption coefficient and the energy bandgaps of ZnTe and ZnSe crystal were measured as 2.01 eV and 2.55 eV respectively. The characteristics of energy transition of ZnTe and ZnSe crystals were investigated as the direct allowed transition by PA spectroscopy. (Author)
[en] An intense infrared free electron laser (IRFEL) causes laser ablation with an emission of visible luminescence from solids samples. In the case of zinc selenide crystals (ZnSe), the focused IRFEL pulse induces the ablation on the surface because of its high peak power density, despite ZnSe being normally transparent to infrared light. The pulsed IRFELs are at 9.2- and 10.2-μm in wavelength and of several GW/cm2 in power density. The luminescent lines can be identified as the neutral atomic lines originating from the target zinc atoms. The pulsed luminescence from ZnSe is short in width and synchronized with the irradiated IRFEL pulses, which is operated at 22.3 MHz. From the relation of the 9.2-μm FEL fluence and luminescent intensity, the threshold of the ZnSe luminescent emission is found to be ∼13 mJ/cm2 at 9.2-μm IRFEL irradiation. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)
[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] On the basis of obtained results we concluded that during treatment of singlet radicals of samples in atmosphere of oxygen by the method of RBQE the incorporation of oxygen atoms into basic ZnSe crystals does not take place. (author)
[en] Traditional Si solar cells have a narrow active absorption cross section among the short wavelength range (200-400 nm). The down-shifting process can efficiently improve the spectral response of Si solar cells by converting shorter wavelengths (i.e., ultraviolet, UV) to longer wavelengths (i.e., the visible range). Here, ZnSe quantum dots (QDs), prepared by an aqueous solution method and employed as a luminescent down-shifting layer, were spin coated onto the upper surface of manufactured Si solar cells. Measurements under standard test conditions (AM1.5, 100 mW/cm2) show that the efficiency of the ZnSe QDs-Si hybrid solar cell is increased from 11.48% to 12%. The improvement of the ZnSe QDs-Si hybrid solar cell is ascribed to the efficient down-shifting process of ZnSe QDs,which enhances spectra response in the UV region for Si solar cells. The mechanism of this optical coupling and efficiency enhancement is investigated in detail. These results support the case that low-cost ZnSe QDs can be employed as efficient downshifting material on large-area solar cells. (author)
[en] Thin films of ZnSe deposited by vacuum evaporation have a high resistivity (>5 x 108 Ω cm), even when donor impurities such as Ga or In and additional Zn are coevaporated. High-conductivity films of ZnSe were produced by annealing films, deposited with coevaporated Ga and Zn, in Zn vapor at 500 0C. Film resistivities in the range 0.5-40 Ω cm were obtained in this way, corresponding to degenerate n-type material with electron densities in the 1019-cm-3 range. Heterojunctions of n-ZnSe/p-CdTe and n-ZnSe/p-GaAs were investigated
[en] Using the Z-scan technique and pump-probe technique with 130 fs laser pulses at 800 nm, we verify that an intraband one-photon absorption follows the interband two photon absorption. Particularly, we find that there is an intraband relaxation interspersed between these two absorption processes for some of the conduction band electrons but not all of them. In this study, we measure the interband two photon absorption coefficient and the absorptive cross sections associated with both excitation pathways within the conduction band. In addition, we estimate the time for relaxation of electrons within the conduction band to be 250 fs.