Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Preparation and characterization of Ga2O3 and GaN nanoparticles [Articol](SPIE, 2015) Rusu, Emil; Ursachi, Veaceslav; Raevschi, Simion; Vlazan, PaulinaIn this communication, we present results on preparation of GaN nanoparticles by conversion of Ga 2O 3 nanocrystals in a flow of NH 3 and H 2. The monoclinic Ga2O 3 nanoparticles have been prepared by hydrothermal method with gallium nitrate and sodium hydroxide as precursors. Ga2O 3 nanowires are produced with increasing the duration of the hydrothermal process up to 24 hours. The production of β-phase Ga2O 3 has been confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. According to XRD, Raman and FTIR spectra, wurtzite type GaN nanocrystals with an average size of 28.6 nm are obtained by nitridation of Ga2O3 nanoparticles. Doping of Ga2O 3 nanomaterial with Eu 3+ ions in the hydrothermal process is demonstrated, and the emission spectra of this Eu-doped nanomaterial are compared with those of Eu-doped nanoparticles prepared previously by solid state reactions.Item Photoluminescence study of Eu-doped Ga2O3 and GaN nanowires and nanoparticles produced by hydrothermal growth [Articol](Editura "Tehnica-UTM", 2015-05-20) Rusu, Emil; Ursachi, Veaceslav; Culeac, Ion; Raevschi, Simion; Vlazan, PaulinaWe present results on preparation of Eu doped GaN nanoparticles and nanowires on the basis of Ga2O3 nanomaterial produced by hydrothermal growth. The monoclinic Ga2O3 nanoparticles and nanowires have been prepared with gallium nitrate and sodium hydroxide as precursors. nanomaterial produced by hydrothermal growth. The monoclinic Ga2O3 nanoparticles and nanowires have been prepared with gallium nitrate and sodium hydroxide as precursors. The geometrical form on the nanomaterial is determined by the duration of the hydrothermal process. The Ga2O3 nanomaterial is transformed unto GaN nanoparticles and nanowires by nitridation in a flow of NH3 and H2. The photoluminescence properties Eu doped Ga2O3 and GaN nanomaterial are investigated under pulsed and continuum wave excitation. The produced material is also investigated by means of XRD analysis, Raman scattering and Fourier transform infrared (FTIR) spectroscopy.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 About the edge luminescence of cadmium sulphide thin layers grown on molybdenum [Articol](Institute of Electrical and Electronics Engineers, 1995-11-11) Raevschi, Simion; Gorceac, Leonid; Coval, Andrei; Chetruș, PetruCdS layers on to molybdenum were synthesized from separate elements in an open flowing hydrogen set. The surface micromorphology and some electrical and photoluminescent properties were investigated. The nature of layers edge photoluminescence peaks are discussed in the frames of the excitated exciton model.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 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 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 Straturi subţiri de CdS depuse din soluţii lichide (baie chimică) [Articol](CEP USM, 2011) Botnariuc, Vasilii; Gorceac, Leonid; Coval, Andrei; Raevschi, Simion; Micli, Valdec; Cinic, BorisThin layers of CdS were deposited on InP (100) substrates with a (3...5) arc degrees misorientation relative to (110) using water solutions of CdSO4, (NH4)2SO4, NH4OH, NH4Cl and CS(NH2)2 for synthesis. The morphology, atomic composition, photoluminescence and electrical properties of the deposited layers were investigated. The morphology of the CdS layers is characterized by a granular structure that is not changing under thermic treatment. A band in the energy interval (1,55 – 3,1) eV at 77 K with the maximum at 2,282 eV is observed in the photoluminescence spectra of the thin layers. Under thermic treatment from 200°C to 500°C in hydrogen the concentration of charge carriers is increasing from 2⋅1017 cm-3 to 2⋅1018 cm-3.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.Item Structura suprafeţei straturilor de AlN depuse pe Si prin metoda HVPE la etapa iniţială de obţinere [Articol](CEP USM, 2010) Raevschi, Simion; Kompan, Mihail; Zhilyaev, Yurii; Gorceac, Leonid; Botnariuc, VasileThe surface structure of AIN layers deposited on the Silicon substrates at the initial stage of germination was studied by the Atomic Force Microscopy (AFM) method. The layers have been deposited by the Hydride Vapor Phase Epitaxy (HVPE) at 1100o C. It was determined that: a) germination follows the 3D model; b) mechanisms of layers growth are changing at the initial deposition stage; c) layers relief can be described in the approximation of a polynomial with elementary Gauss functions as arguments.