2. Articole
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Item SYNTHESIS AND PROPERTIES OF AL-DOPED ZnO THIN FILMS FOR PHOTOVOLTAICS(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 HIGH TEMPERATURE ULTRA-FAST GALLIUM ARSENIDE RECTIFIER DEVICES(Institute of Electrical and Electronics Engineers Inc., 2012-10-20) Baranov, Simion; Gorceac, Leonid; Cheibaș, VictorThe report is related to the high temperature electronics field. The industrial developed country practice demonstrates that up to 70% of the fabricated electrical energy passes through semiconductor converters. Only in the field of electrical drive, which uses about 50% from the produced electrical energy, passing to the frequency converter of the asynchronous drives speed control, brings an energy economy up to 25%. In the electrical transport with the energy braking recovering the economy is more than 30%. The present elaboration is foreseeing the improvement of the technological production route of gallium arsenide (GaAs) power semiconductor devices (PSD), by introducing some innovative technological processes as: (1) GaAs epitaxial technology in the Ga-AsCl 3-H2 system; (2) epitaxial structures divided into crystals by chemical method; (3) GaAs p-n junction passivation by own oxide (Ga2 O3) precipitate on the divided surface of the crystal. The goal of the project is increasing manufacturing efficiency (ME) at the GaAs power devices with more than 600 V of voltage fabrication. The proposed improvements are increasing ME with 40% and are expanding the blocking voltage interval up to 1000 V. As a result a new product was elaborated and proposed to the manufacturing– the ultra-fast current converter with 80 ns of recovery time, stable at high temperature (200 oC) and 4.5 kV of blocking voltage, that outrun the characteristics of commercial product ESJC30-05(0.3 s, 110 oC).Item AUTOMATION CONTROL SYSTEM OF THE ALLOYING PROCESS OF GALLIUM ARSENIDE LAYERS GROWTH BY EPITAXIAL TECHNOLOGY(Institute of Electrical and Electronics Engineers Inc., 2012-10-20) Baranov, Simion; Cojuhari, Irina; Izvoreanu, Bartolomeu; Gorceac, LeonidThis paper proposes to control the thermal alloying process of GaAs epilayers growth by transport reaction in Ga- AsCl 3-H2 system. The thermal alloying process is controlled by using the universal two-channel programmable PID-controller TRM151, which permits automatic control of complicated objects with high precision. The thermal process was identified using the parametric model ARX (Auto-Regressive eXogenous) from System Identification Toolbox from MATLAB. The experimental technologist’s program contains steps of p +- po –n + photovoltaic structures achievement with damper layer on p-GaAs substrate. There is a possibility to obtain multiple periodical epitaxial layers structures with different dimensions and electro-physical properties, including nano-dimension structures, changing different steps of production. The tuning controller was performed using the maximal stability degree method. This control system minimizes the new technologies elaboration terms, accelerates the implementation of the elaborated technology in industry by reducing production costs, improving the product quality and its market competitiveness.Item NUCLEAR QUADRUPOLE RESONANCE OF MIXED-VALENCE CHARGE-ORDERED DIMERS(1999) Clochișner, Sofia; Gorceac, LeonidThe influence of an external magnetic field on the conditions of charge ordering of mixed-valence dimer clusters Ni 2q–Niq is considered. The manifestations of charge ordering in the spectra of nuclear quadrupole resonance are elucidated. These spectra are shown to give information on the key parameters of charge-ordered crystals.Item THE CARACTERIZATION OF THE CdS-BASED SOLAR CELL HETEROJUNCTIONS(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(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 AERO-ZNS ARCHITECTURES WITH DUAL HYDROPHILIC–HYDROPHOBIC PROPERTIES FOR MICROFLUIDIC APPLICATIONS(2020) Pleșco, Irina; Braniște, Tudor; Wolff, Niklas; Gorceac, Leonid; Duppel, Viola; Cinic, Boris; Mishra, Yogendra Kumar; Sarua, Andrei; Adelung, Rainer; Kienle, Lorenz; Tighineanu, IonHere, we report on a new aero-material, called aero-ZnS, representing self-organized architectures made of ZnS hollow micro-tetrapod struc- tures with nanoscale thin walls. The fabrication process is based on the hydride vapor phase epitaxy of CdS on sacrificial micro-tetrapods of ZnO with simultaneous or subsequent transformation of CdS into ZnS and removal of the sacrificial ZnO crystals. The nanostructure of the obtained ZnS hollow micro-tetrapods exhibits the polytypic intergrowth of wurtzite- and sphalerite-type phases perpendicular to their close packed planes. The inner surface of the micro-tetrapod walls preserves oxygen sites, as demonstrated by imaging based on electron energy- loss filtering. The self-organized aero-ZnS architecture proves to be hydrophilic under tension and hydrophobic when compressed against water. Self-propelled liquid marbles assembled using ZnS hollow micro-tetrapod structures are demonstrated.Item CdS NANOMETRIC LAYERS GROWN ON SnO2 COATED GLASS SUBSTRATES FOR PHOTOVOLTAIC DEVICES(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 AlN FILMS GROWTH ON Si (III) BY HYDRIDE VAPOR PHASE EPITAXY(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 PROPRIETĂŢILE ELECTRICE ALE CELULEI FOTOVOLTAICE CU JONCŢIUNE RELIEFATĂ FABRICATĂ PRIN HVPE(Editura "Tehnica-UTM", 2014-10-22) Baranov, Simion; Gorceac, Leonid; Cinic, BorisIn this report we are represented the electro-physical properties of the photovoltaic cell with single relief junction fabricated on gallium arsenide substrate by HVPE method. This cell have the shunt resistance of 3.8 time bigger then the plane one, that it demonstrates the decrease of energy losses on the cell surface. It increases the efficiency of charges gathering (78 % of the full coefficient). It was used the AFM and RAMAN methods of investigation.