Browsing by Author "Colibaba, Gleb"

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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)
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.
FABRICAREA STRUCTURILOR SnO2/CdTe/ZnO ŞI CERCETAREA PROPRIETĂŢILOR ACESTORA
(CEP USM, 2020) Lungu, Ion; Colibaba, Gleb; Potlog, Tamara
GROWTH TECHNOLOGY FOR ZnSe SINGLE CRYSTALS WITH LOW DISLOCATION DENSITY
(2008) Colibaba, Gleb; Nedeoglo, Dmitrii
The influence of the growth temperature, undercooling, growth rate as well as growth chamber construction and furnace temperature profile on the structural perfection of the crystals grown by both physical and chemical vapors transport has been investigated. The conditions for growing of crystals free from subgrain boundaries and twins are suggested. The etch pits are not observed in the basic volume (up to 4 сm3) of grown crystals. It is shown, that PL spectra of as-grown ZnSe crystals consist of the edge radiation only. The resistivity of ZnSe crystals annealed in a Zn melt is higher than 108 Ohmcm, whereas the electrical conductivity of ZnSe:I crystals grown by chemical vapor transport and annealed in a Zn melt is 10 (Ohm⋅cm)-1 at room temperature.
HALIDE-CARBON VAPOR TRANSPORT OF ZnO AND ITS APPLICATION PERSPECTIVES FOR DOPING WITH MULTIVALENT METALS
(Elsevier, 2018) Colibaba, Gleb
The growth of ZnO single crystals in closed ampoules using HCl+C mixture as a chemical vapor transport agent (TA) was studied. The influence of growth temperature, TA density, C/HCl ratio, and undercooling on the ZnO mass transport rate was investigated theoretically and experimentally. The influence of growth medium composition on the features of crystal growth, such as the minimization of growth nucleus density, the increase in the lateral growth rate of up to 1 mm per day, the suppression of the attachment effect, and stable growth of non-polar, semi-polar and polar planes of a hexagonal structure was analyzed. The structural, photoluminescent, optical and electrical properties were investigated. The doping efficiency of ZnO by oxides of metals was analyzed for various TAs and Zn pressure in the growth medium. The possibility of increase in the doping efficiency by several orders of magnitude for multivalent metals was predicted for HCl+C TA.
HALIDE-OXIDE CARBON VAPOR TRANSPORT OF ZnO: NOVEL APPROACH FOR UNSEEDED GROWTH OF SINGLE CRYSTALS WITH CONTROLLABLE GROWTH DIRECTION
(Elsevier, 2018) Colibaba, Gleb
The thermodynamic analysis of using HCl + CO gas mixture as a chemical vapor transport agent (TA) for ZnO single crystal growth in closed ampoules, including 11 chemical species, is carried out for wide temperature and loaded TA pressure ranges. The advantages of HCl + CO TA for faster and more stable growth are shown theoretically in comparison with HCl, HCl + H2 and CO. The influence of the growth temperature, of the TA density, of the HCl/CO ratio, and of the undercooling on the ZnO mass transport rate was investigated theoretically and experimentally. The HCl/CO ratios favorable for the growth of m planes and (0001)Zn surface were found. It was shown that HCl + CO TA provides: (i) a rather high growth rate (up to 1.5 mm per day); (ii) a decrease of wall adhesion effect and an etch pit density down to 103 cm−2; (iii) a minimization of growth nucleus quantity down to 1; (iv) stable unseeded growth of the high crystalline quality large single crystals with a controllable preferred growth direction. The characterization by the photoluminescence spectra, the transmission spectra and the electrical properties are analyzed.
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.
NOVEL APPROACH FOR CALCULATING THE CHARGE CARRIER MOBILITY AND HALL FACTOR FOR SEMICONDUCTOR MATERIALS
(Elsevier, 2018) Colibaba, Gleb
The additive Matthiessen's rule is the simplest and most widely used rule for the rapid experimental characterization and modeling of the charge carrier mobility. However, the error when using this rule can be higher than 40% and the contribution of the assumed additional scattering channels due to the difference between the experimental data and results calculated based on this rule can be misestimated by several times. In this study, a universal semi-additive equation is proposed for the total mobility and Hall factor, which is applicable to any quantity of scattering mechanisms, where it considers the energy dependence of the relaxation time and the error is 10–20 times lower compared with Matthiessen's rule. Calculations with accuracy of 99% are demonstrated for materials with polar-optical phonon, acoustic phonon via the piezoelectric potential, ionized, and neutral impurity scattering. The proposed method is extended to the deformation potential, dislocation, localized defect, alloy potential, and dipole scattering, for nondegenerate and partially degenerate materials.
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
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
OBŢINEREA STRATURILOR SUBŢIRI DE ZnO CU CONDUCTIBILITATE ÎNALTĂ PRIN PULVERIZARE MAGNETRON A ŢINTELOR PREPARATE ÎN VAPORI HALOGENICI
(CEP USM, 2020) Rusnac, Dumitru; Fedorov Vladimir; Colibaba, Gleb
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.
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.
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.