2. Articole
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Item SINTERING HIGHLY CONDUCTIVE ZnO:HCl CERAMICS BY MEANS OF CHEMICAL VAPOR TRANSPORT REACTIONS(Elsevier, 2019) Colibaba, GlebThe 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.Item EFFECT OF p-NiO INTERLAYER ON INTERNAL QUANTUM EFFICIENCY OF p-GaN/n-ZnO LIGHT-EMITTING DEVICES(American Scientific Publishers, 2015) Sirkeli, Vadim; Yilmazoglu, Oktay; Küppers, Franko; Hartnagel, HansWe report on numerical investigations of p-GaN/n-ZnO light-emitting devices with p-NiO interlayer, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current–voltage dependences of investigated LEDs show a threshold voltage of 3.1 V and 5.4 V for the LED devices without and with presence of p-NiO interlayer, respectively. It is found that p-NiO layer act as electron blocking layer, that lead to the enhance of charge carriers confinement in active region, and to the increasing of internal quantum efficiency (IQE) of LED device up to 0.5%, that in four times higher in compare with that for original p-GaN/n-ZnO LED device.Item EFFECT OF p-NiO AND n-ZnSe INTERLAYERS ON THE EFFICIENCY OF p-GaN/n-ZnO LIGHT-EMITTING DIODE STRUCTURES(IOP Publishing Ltd, 2015) Sirkeli, Vadim; Yilmazoglu, Oktay; Küppers, Franko; Hartnagel, HansWe report on a numerical study of the characteristics of p-GaN/n-ZnO light-emitting diodes (LEDs) with p-NiO and n-ZnSe interlayers, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current-voltage dependences of investigated LEDs show a threshold voltage of 3.1 V, 5.4 V and 5.6 V for LED devices without and with the presence of p-NiO and n-ZnSe interlayers, respectively. It is found that p-NiO, n-ZnSe and n-ZnO interlayers act as an electron blocking layer, active media layer, and electron transport layer, respectively. It is established that the insertion of both p-NiO and n-ZnSe interlayers leads to the enhancement of charge carrier-confinement in the active region and to the significant increase of internal quantum efficiency (IQE) of the LED device up to 82%, which is comparable with IQE values in order to obtain better AlGaN- and InGaN-based LEDs. It is found that the efficiency of LED devices at 100 A cm−2 is equal to 0.024, 0.09 and 16.4% of external quantum efficiency (EQE), 1.3 × 10−4, 1.6 × 10−4, and 6.4 lm W−1 of PE, and 1.3 × 10−4, 2.9 × 10−4, and 12 cd A−1 of CE for p-GaN/n-ZnO, p-GaN/p-NiO/n-ZnO, and p-GaN/p-NiO/n-ZnSe/n-ZnO LED devices, respectively.Item ЛЮМИНЕСЦЕНТНЫЕ ХАРАКТЕРИСТИКИ ТОНКИХ ПЛЁНОК ОКСИДА ЦИНКА, ПОЛУЧЕННЫХ МЕТОДОМ ЭЛЕКТРОФОРЕЗА(CEP USM, 2012) Гоглидзе, Т.И.; Дементьев, И.В.; Задорожный, А.П.; Коваль, А.В.; Петренко, П.А.; Гашин, П.А.Показана возможность осаждения тонких однородных слоёв оксида цинка с низкой проводимостью электрофоретическим методом. Представлены результаты измерений фотолюминесценции тонких слоёв ZnO при температурах 300 К и 77 К.Item ZnO DOPING EFFICIENCY BY MULTIVALENT METALS IN COMPLEX CVT REACTIONS(Elsevier, 2019) Colibaba, GlebThe 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.Item HALIDE-CARBON VAPOR TRANSPORT OF ZnO AND ITS APPLICATION PERSPECTIVES FOR DOPING WITH MULTIVALENT METALS(Elsevier, 2018) Colibaba, GlebThe 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.Item HALIDE-OXIDE CARBON VAPOR TRANSPORT OF ZnO: NOVEL APPROACH FOR UNSEEDED GROWTH OF SINGLE CRYSTALS WITH CONTROLLABLE GROWTH DIRECTION(Elsevier, 2018) Colibaba, GlebThe 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.Item THE INVESTIGATION OF TCO/CdS/CdTe HETEROJUNCTIONS BY C-U and C-f MEASUREMENTS: EXPERIMENT AND MODELING(IEEE, 2013) Rotaru, Corneliu; Vatavu, Sergiu; Fedorov, Vladimir; Gașin, Petru; Lux-Steiner, Martha; Ferekides, Chris; Rusu, MarinThe paper presents the analysis of C-U and C-f data obtained in the 1 kHz-10 MHz range for CdS/CdTe heterojunctions prepared by CSS onto (ZnO:Al, ZnO:Al/i-ZnO)/Glass substrates. An attempt to model the physical properties of the heterojunctions is made. A small signal analysis has been carried out to establish the equivalent circuit of device. The unusual capacitance behavior of the ZnO based heterojunction is attributed to presence of the barrier at the back contact.Item STRATURI SUBŢIRI DE OXID DE ZINC CRESCUTE PRIN METODA PULVERIZĂRII ÎN FLUX DE ARGON(CEP USM, 2018) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Cinic, Boris; Gaugaș, Petru; Chetruș, Petru M.; Moldovanu, Sergiu; Raevschi, SimionStraturile subţiri de ZnO au fost crescute din acetat de zinc dizolvat în apă-acid acetic-metanol cu o molaritate de 0,2 M folosind metoda pulverizării în intervalul de temperaturi (250-450)°C în flux de argon. Au fost cercetate proprietăţile optice şi electrice ale acestor straturi în dependenţă de temperatura de creștere. Transmitanţa în diapazonul de lungimi de undă (300-1000) nm are valori de 80-85%. Rezistenţa specifică a straturilor subțiri de ZnO crescute la 450°C după tratarea termică în vid şi hidrogen la 450°C timp de o oră se micșorează de la 33 •cm până la 0,028 •cm. Recombinarea radiantă în straturile de ZnO este însoțită de tranziții pe niveluri adânci și de tranziții bandă-bandă la interacțiunea purtătorilor de sarcină cu fononii de tip LO.Item OPTICAL PROPERTIES OF ZnO THIN FILMS OBTAINED BY HEAT TREATMENT OF Zn THIN FILMS ON AMORPHOUS SiO2 SUBSTRATES AND SINGLE CRYSTALLINE GASE LAMELLAS(Elsevier, 2016) Dmitroglo, Liliana; Evtodiev, Igor; Untila, DumitruOptical absorption and photoluminescence of polycrystalline ZnO films obtained by thermal oxidation of Zn thin films deposited on amorphous SiO 2 (quartz) and (0001) surface of single crystalline GaSe lamellas have been investigated. The absorption edge of submicrometric ZnO films on quartz is determined by direct transitions corresponding to an optical band gap of 3.88 eV, at 300 K. For ZnO films with thickness between 1.5 and 10 μm, the absorption threshold is of excitonic nature. Photoluminescence of polycrystalline ZnO films on amorphous quartz reaches its maximum in the orange spectral range, while that of ZnO films on oriented single crystalline GaSe substrate covers the entire visible range. [ABSTRACT FROM AUTHOR]