2. Articole

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Author: search.filters.author.Colibaba, GlebHas files: Yes

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    OBTAINING HIGHLY CONDUCTIVE OXIDE SINGLE CRYSTALS FOR MANUFACTURING NANOTEMPLATES
    (2019) Colibaba, Gleb; Monaico, E.; Rusnac, D.
    The present investigation is devoted to obtaining ZnO, In2O3 and Ga2O3 single crystals by chemical vapor transport (CVT). The thermodynamic analysis of the composition of CVT systems with ZnO, In2O3, Ga2O3 and various transport agents (TAs) is carried out for wide temperature range and for various density/composition of TA. The influence of the growth temperature and of the TA density/composition on the mass transport rate is investigated theoretically and experimentally. The possibility of increase in mass transport rate by several orders of magnitude at the presence of compound TAs is demonstrated. The application prospects of obtained single crystals as substrates for manufacturing nanoporous matrices (nanotemplates) by the electrochemical etching are analyzed. The fabrication of nanopore arrays with various morphology, which depends on the crystallographic orientation of substrates, is demonstrated for ZnO
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    FABRICAREA STRUCTURILOR SnO2/CdTe/ZnO ŞI CERCETAREA PROPRIETĂŢILOR ACESTORA
    (CEP USM, 2020) Lungu, Ion; Colibaba, Gleb; Potlog, Tamara
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    STRUCTURAL AND OPTICAL PROPERTIES OF ZNO:GA THIN FILMS DEPOSITED ON ITO/GLASS SUBSTRATES FOR OPTOELECTRONIC APPLICATIONS
    (Academia de Ştiinţe a Moldovei, 2021) Rusnac, Dumitru; Lungu, Ion; Colibaba, Gleb; Potlog, Tamara
    Doped (with GaCl3), undoped ZnO and ITO/ZnO:Ga nanostructured thin films are synthesized using the spray pyrolysis method. The doped ZnO thin films are synthesized at the atomic ratio of Ga/Zn added in the starting solution fixed at 1, 2, 3, and 5. Gallium-doped ZnO films synthesized on glass/ITO substrates are annealed at 4500C in different environments: vacuum, oxygen, and hydrogen. X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and current–voltage (I–V) measurements are applied to characterize the structural properties, composition, surface morphology, and electrical properties of ZnO:Ga nanostructured thin films. X-ray diffraction analysis shows that ZnO:Ga films deposited on glass substrates have a dense and homogeneous surface with a hexagonal structure. The ZnO:Ga films deposited on glass/ITO substrates are composed of two phases, namely, hexagonal ZnO and cubic ITO. The I–V characteristics show the presence of good ohmic contacts between Al and In metals and ZnO:Ga thin films regardless of the nature of the substrate and the annealing atmosphere.
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    EFFECTS OF IMPURITY BAND IN HEAVILY DOPED ZnO:HCl
    (Elsevier, 2019) Colibaba, Gleb; Avdonin, A.; Shtepliuk, I.; Caraman, Mihail; Domagała, J.; Inculeț, Ion
    A comparative study of properties of ZnO:HCl single crystals obtained by various methods is presented. Characterization by photoluminescence, optical and electrical measurements in the wide temperature range has allowed to analyze the energy spectra of Cl-containing stable defects in ZnO. Presence of shallow Cl donors, deeper donor complexes, incorporating several Cl atoms or stable H-Cl pairs and presence of compensating deep acceptors, attributed to VZnClO centers, are demonstrated. The presence of shallow donor impurity band, as well as strong dependence of its activation energy on the doping level is shown. The controversy of various models for estimation of this dependence is discussed. It is demonstrated, that 90% of this dependence is caused by feature of temperature dependence of Hall coefficient related to conductive impurity band, and a more correct equation for activation energy is suggested. An abnormally low efficiency of neutral impurity scattering of charge carriers and strong optical absorption in the near-IR spectral range are demonstrated and attributed to upper conductive impurity band of negatively charged donors with an extra electron.
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    SINTERING HIGHLY CONDUCTIVE ZnO:HCl CERAMICS BY MEANS OF CHEMICAL VAPOR TRANSPORT REACTIONS
    (Elsevier, 2019) Colibaba, Gleb
    The features of sintering ZnO ceramics by means of chemical vapor transport (CVT) in sealed quartz chambers were investigated. CO, C, H2, HCl, HCl + H2, HCl + C, HCl + Zn and HCl + H2+ C mixtures were used as transport agents (TAs) at the 925–1070 °C temperature range. The exact thermodynamic analysis of compound CVT systems, carried out for wide temperature and loaded TA pressure ranges, was applied to establish the relation between medium composition and the characteristics of sintered materials. The advantages of some compound TAs based on HCl were shown. ZnO:HCl ceramics with a diameter of 25 mm (99 ± 1% of the initial diameter of the sintering powder), a density of 5.1 ± 0.3 g/cm3, a hardness of 2.0 ± 0.2 GPa, a resistivity of 2.4⋅10-2 Ω cm, and a controllable stoichiometric deviation, were obtained. The investigated materials have no contamination from metallic Zn, ZnCl2 or solid C. The doping efficiency of ZnO ceramics by oxides of various metals, by means of low temperature CVT reactions with ZnCl2 vapors as a TA, was calculated for oxides of all non-radioactive metals of the periodic table.
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    OBTAINING OF II-VI COMPOUND SUBSTRATES WITH CONTROLLED ELECTRICAL PARAMETERS AND PROSPECTS OF THEIR APPLICATION FOR NANOPOROUS STRUCTURES
    (John Wiley & Sons, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Monaico, Eduard; Tiginyanu, Ion
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    A COMPARATIVE ANALYSIS OF INFRARED LUMINESCENCE SPECTRA OF ZnSe:Yb, ZnSe:Gd, AND ZnSe:Cr CRYSTALS
    (Wiley, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia
    Photoluminescent and optical properties of ZnSe crystals doped with Yb and Gd rare-earth elements (REEs) and Cr impurity are investigated in infrared (IR) spectral range. The influence of stoichiometric deviation on photoluminescence (PL) spectra of the crystals is investigated and the structure of complex IR PL bands is analysed. The good coincidence between the IR PL spectra of the samples doped with Yb, Gd, and Cr is shown. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the composition of IR PL spectra by enrichment of the samples with Zn or Se is discussed. The model that explains the formation of associative centres based on the REEs and background Cu impurity fixed in the nodes of crystal lattice with tetrahedral symmetry, which are responsible for IR PL bands, is proposed. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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    INFRARED PHOTOLUMINESCENCE OF ZnSe:GD CRYSTALS
    (Elsevier, 2015) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia
    Photoluminescent and optical properties of ZnSe crystals doped with Gd impurity are investigated in infrared (IR) spectral range. The influence of crystal growth temperature, impurity concentration, stoichiometric deviation and post-annealing cooling rate, concentration of Cr and Cu background impurities, temperature and excitation level on photoluminescent and optical properties of the samples is studied. Based on these investigations, the structure of complex IR photoluminescence (PL) bands is analyzed. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the IR PL spectra by enrichment of the samples with Zn or Se is discussed. Coincidence of the IR PL spectra structure is shown for the samples doped with Gd, Yb, and Cr impurities. The model that explains the formation of complexes based on rare-earth elements (REEs) and Cr and Cu background impurities fixed in the nodes of crystal lattice with tetrahedral symmetry, responsible for IR PL bands, is proposed.
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    ZnO DOPING EFFICIENCY BY MULTIVALENT METALS IN COMPLEX CVT REACTIONS
    (Elsevier, 2019) Colibaba, Gleb
    The present investigation is a theoretical study of doping efficiency of ZnO crystals grown by using compound chemical vapor transport (CVT) agents based on HCl and doped by oxides of various metals in the growth process. The thermodynamic analysis for compositions of MexOy−ZnO–ZnCl2–CO CVT systems in the closed growth chambers was carried out for oxides (MexOy) of all non-radioactive metals of the periodic table, taking into account various types of chloride species. The influence of temperature (1000–1500 K), ZnCl2 pressure (10−2−10 atm) and Zn pressure (10−5−3 atm) on the total pressure and mass transport rate of doping species (MeCln) were investigated. The possibility of increase in the doping efficiency of ZnO by MexOy + ZnCl2 + Zn CVT reactions is predicted for some multivalent metals. Some calculation results are confirmed experimentally.