Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Synthesis and properties of Al-doped ZnO thin films for photovoltaics [Articol](Institute of Electrical and Electronics Engineers Inc., 2018-11-27) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Gorceac, Leonid; Raevschi, Simion; Taku, Miyake; Worasawat, Suchada; Mimura, HidenoriPolycrystalline undoped and Al-doped ZnO thin films were deposited by spray pyrolysis using oxygen and argon atmospheres. The influence of postdeposition vacuum annealing on the structure, morphology and optical properties was studied by X-ray diffraction, atomic force microscopy and UV–VIS spectroscopy. The thermal vacuum annealing induces structural and morphological changes, especially in Al-doped ZnO thin films synthetized in oxygen atmosphere. Further on, the electrical conductivity in dependence of the nature of gas atmosphere and Al concentration is discussed.Item The caracterization of the CdS-based solar cell heterojunctions [Articol](Institute of Electrical and Electronics Engineers Inc., 2010-10-11) Potlog, Tamara; Botnariuc, Vasile; Gorceac, Leonid; Spalatu, Nicolae; Maticiuc, Natalia; Raevschi, SimionThe CdS-based solar cell heterojunctions (HJ) have been obtained by growth of CdS at relatively lower temperature using the close space sublimation method(CSS). Investigation of the photovoltaic characteristics shows an efficiency of about 12 % for InP/CdS and 9.6 % for CdS/CdTe solar cell HJ. The analysis of the forward dark current-voltage and the capacitance-voltage characteristics indicate a tunnelling recombination current which flows through states near or at the interfaces of a thermal energy of about 0.62 eV for CdS/CdTe and 0.42 eV for InP/CdS solar cell heterojunctions. The solar energy conversion efficiency is influenced by the interface states through the open circuit voltage and the fill factor.Item CdS nanometric layers grown on SnO2 coated glass substrates for photovoltaic devices [Articol](2012) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Chetruș, Petru; Cinic, Boris; Raevschii, Simion; Micli, ValdecCdS layer thickness decreases at high substrate temperatures due to the fact that a part of CdCl2/(NH2)2 CS aqueous solution evaporates without reaching the substrate surface. CdS layers deposited at the substrate temperature from 250oC to 450oC are growing with a deficit of sulfur. CdS layers with better stoichiometry were grown in the conditions when in the solutions, used for CdS layers growing, there is an excess of thiourea (CdCl2/ TU =1:2). The high charge carrier concentration of 1020cm-3 in CdS layers grown on glass substrates coated with SnO2 layer is related to Sn doping of the layers from SnO2 layer.Item Thin AIN films growth on Si (III) by hydride vapor phase epitaxy [Articol](2008) Raevschi, Simion; Davydov, Valerii; Zhilaev, Yurii; Gorceac, Leonid; Botnariuc, VasileThin AlN layers have been grown on Si (111) by hydride vapor phase epitaxy (HVPE) method in a horizontal quartz reactor. The surface of layers has been studied by scanning electron microscopy and by the Raman spectroscopy method and found to have the structured morphology. It has been determined that the layers have high specific electrical resistance and are strained in the plane of the substrate.Item Effect of carrier gas and vacuum annealing on the physical properties of ZnO thin films doped with gallium by chemical spray pyrolysis [Articol](Editura "Tehnica-UTM", 2018-05-24) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Raevschi, Simion; Worasawat, Suchada; Mimura, Hidenori; Gorceac, LeonidStructural, optical and electrical properties of zinc oxide thin films doped with 2% Ga, annealed in the vacuum at the same temperature and obtained onto glass substrates by the chemical spray pyrolysis method in the different gas atmospheres were investigated by X-ray Diffraction (XRD), UV-VIS spectrophotometry and Hall measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c-axis orientation. All ZnO:Ga thin films had higher than 80 % transmittances in the visible region. Doping with 2% Ga led to a decrease in the optical band gap indifferent of the nature of the carrier gas. The synthesis of ZnO thin films with 2% Ga doping and annealing in the same conditions in Ar and O2 atmospheres led to the lower conductivity with electron concentration of 1016 cm−3.Item Stanat de cadmiu obţinut prin metoda pulverizării [Articol](CEP USM, 2013-09-26) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Inculeţ, Ion; Chetruş, Petru; Raevschi, SimionItem Straturi nanometrice SnO2 pentru structuri fotovoltaice [Articol](CEP USM, 2014) Botnariuc, Vasile; Gorceac, Leonid; Cinic, Boris; Inculeţ, Ion; Raevschi, SimionItem Proprietăţi electrofizice ale straturilor de CdS obţinute prin metoda pulverizării cu tratare termică în hidrogen [Articol](CEP USM, 2012) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Cinic, Boris; Chetruș, Petru; Raevschi, Semion; Banu, SimionPrin metoda pulverizării chimice au fost crescute straturi de CdS din soluţii apoase de CdCl2/(NH2)2 CS cu molaritatea de 0,1 M în intervalul de temperaturi (250...450)°C. Straturile au fost tratate termic în flux de hidrogen timp de 20 min la temperaturile de 350 şi 450°C. Au fost cercetate proprietăţile electrofizice şi fotoluminescenţa acestor straturi. În straturile depuse la 450°C cu mărirea temperaturii de tratare până la 450°C se observă o uşoară micşorare a concentraţiei purtătorilor de sarcină. Spectrul fotoluminescenţei prezintă o fâşie largă în intervalul de energii 1,6...2,6 eV. Se observă un vârf al fotoluminescenţei cu energia de 1,95 eV, care se deplasează cu mărirea temperaturii de creştere a straturilor de CdS şi atinge valoarea de 2,5 eV pentru straturile crescute la temperatura de 450°C.Item Straturi CdS crescute pe suporturi de sticlă prin metoda pulverizării [Articol](CEP USM, 2012) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Chetruș, Petru; Cinic, Boris; Raevschi, Simion; Micli, ValdecCdS layers were grown from aqueous solutions of cadmium chlorine (CdCl2) and thyourine (NH2)2 CS with the molarity of 0,1 M by pulverization method in the temperature range of (250...450)°C. CdS layers were grown on glass substrates covered with a previously deposited SnO2 layer. The deposited CdS layers morphology, atomic weight and composition were studied biasing a sunning electron microscope (SEM). The morphology, atomic weight and composition of the deposited CdS layers considerably changes with the increase of the deposition temperature. The charge carriers’ concentration and their mobility in CdS layers deposited at different temperatures were measured and estimated.Item Evoluarea particulelor dispersate de ALN depuse pe si prin metoda HVPE la etapa de formare a stratului continuu [Articol](CEP USM, 2011) Raevschi, Simion; Kompan, Mihail; Zhilyaev, Yurii; Gorceac, Leonid; Botnariuc, VasileEvolution of growth of the disperse particles of AlN which has been grown up on substrates of silicon during formation of a continuous layer are studies by AFM (Atomic Force Microscopy ) method. Layers have been grown up by HVPE (Hydride Vapor Phase Epitaxy) method at 1100o C. It is established: a) nunucleation occurs according to three dimensional model; b) layers are formed of two categories of disperse particles; c) growth rate of categories differ; d) at an initial stage of growth there is a latent period of time when superficial concentration of disperse particles remains to a constant.
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