2. Articole
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Item Crystalline structure, surface morphology and optical properties of nanolamellar composites obtained by intercalation of InSe with Cd [Articol](2015) Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Canțer, Valeriu; Spalatu, Nicolae; Leontie, Liviu; Dmitroglo, Liliana; Luchian, EfimiaA material composed of InSe and CdSe crystallites was obtained by heat treatment at 753K of InSe single crystalline plates in Cd vapour for 3÷24 hours. The average diameters of CdSe and InSe crystallites determined from diffraction lines analysis are respectively equal to 20 nm and 22 nm. The photoluminescence spectra at 300K and 80K of composite decompose well into two Gaussian curves, one is in good correlation with the photoluminescence of CdSe crystals and the other is shifted to higher energies than the width of the band gap of CdSe crystals.Item Electrical properties of thermally annealed CdS thin films obtained by chemical bath deposition [Articol](Institute of Electrical and Electronics Engineers Inc., 2011-10-17) Scorțescu, Dumitru; Maticiuc, Natalia; Nicorici, Valentina; Spalatu, Nicolae; Potlog, Tamara; Hiie, Jaan; Valdna, VelloElectrical conductivity and the Hall-effect are investigated in the temperature interval (80-400) K on thermally annealed in H 2 CdS thin films obtained by chemical bath deposition. Different characters of the temperature dependence of conductibility are observed in the CdS films annealed at different temperatures. The Hall measurements allow calculating the values of the NA , N D , n ex and ED . According to Hall measurements the CdS films show several donor levels at different energetic depths in dependence of the annealing temperature. The sample annealed at high temperatures than 350oC proves to be compensated with a sharply decreasing electrical conductivity with the temperature decrease.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 Photoelectric and photoluminescence properties of CdTe–GaTe composite [Articol](2016) Caraman, Iuliana; Spalatu, Nicolae; Evtodiev, Igor; Untila, Dumitru; Leontie, Liviu; Caraman, MihailA GaTe–CdTe composite was obtained by thermal treatment at 1020 K of GaTe single crystals in Cd vapor atmosphere. The composite photoluminescence, photoconductivity, and com- position are studied in this work. The photosensitivity and photoluminescence band structure are determined for both the primary crystals and the composite. The CdTe crystallites create, in the GaTe bandgap, recombination and trapping levels, which determine the structure of the photoluminescence spectra and the spectral range of composite photosensitivity. The photoluminescence spectrum of the composite at 80 K contains characteristic bands of both composite components, GaTe and CdTe. From the analysis of thermally stimulated luminescence curves, the energies of the electron trapping levels in the composite are determined.Item Optical properties of GaTe-ZnTe nanolamellae composite [Articol](2015) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Evtodiev, Silvia; Rotaru, Irina; Caraman, Mihail; Untilă, DumitruA material composed of GaTe and ZnTe crystallites with average diameter of ~ 37 nm and 68 nm respectively was obtained by heat treatment at the temperature of 1000K and 1073K of GaTe plates in Zn vapour for 24 hours. The absorbance spectra of composite material obtained at 1073K and that calculated from diffuse reflection using the Kubelka-Munk formula contains the bands characteristic for light absorption in ZnTe and GaTe crystallites. The photoluminescence spectrum of composite material at the temperature of 80K is composed to the excitonic band in GaTe and impurity bands of ZnTe crystallites.Item Morfologia suprafeţei şi proprietăţile optice şi fotoelectrice ale heterojoncţiunilor CdTe-GaTe [Articol](CEP USM, 2014) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Leontie, Liviu; Rotaru, Irina; Until, Dumitru; Caraman, MihailItem Optical and Photoelectric Properties of Nanolamellar Structures Obtained by Thermal Annealing of InSe Plates in Zn Vapours [Articol](2018) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Spalatu, Nicolae; Dmitroglo, Liliana; Caraman, MihailThe structural, optical and photoelectric properties of InSe crystals grown by Bridgman–Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe‐InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS‐NIR spectral region.Item Elaborarea tehnologiei de fabricare a celulelor solare ITO/CdS/CdTe pe suporturi flexibile [Articol](CEP USM, 2007) Potlog, Tamara; Spalatu, Nicolae; Caproş, NinaThe development of high efficiency, stable, lightweight and flexible solar cell is important for terrestrial and space applications. We have developed a novel process to make solar cells on flexible polymer sheets. A thin layer of CdTe compound semiconductor is used for the absorption of solar light and generation of electrical current. In this work the solar electricity conversion efficiency of 4,66% is the highest efficiency reported for a solar cell grown on a polymer sheet.Item Caracterizarea heterostructurilor CdS/CdTe/Te cu ajutorul caracteristicilor capacitate-tensiune [Articol](CEP USM, 2009) Potlog, Tamara; Spalatu, Nicolae; Maticiuc, NataliaThin Film CdS/CdTe heterojunctions were fabricated by close space sublimation at the substrate temperature 340 ± 5ºC and evaporator temperature 610oC± 5ºC. Capacitance-voltage characteristics in the region of temperatures 313 K – 363 K were measured. Was established that the capacitance of heterojunction CdS/CdTe/Te increases from 658 (cm2/pF)2, T=313 K to 1096 (cm2/pF)2, T=393 K. The width space charge region at room temperature is 7,4 μm, but at the tempera-ture of 393 K are 0,15 μm. In the above mentioned temperature region the potential contact barrier height decreases from 0,8 V at room temperature (293 K) up to 0,12 V at the temperature of 393K. The ionized-charge concentration profi le (NA-ND)is not constant, but it is increasing together with the enlarging of the depth of heterojunction and measure tem-perature, indicating to a high density of the states in the space charge regionItem Cercetări XRD și XPS ale straturilor de AIN, AlGaN, GaN depuse pe siliciu prin metoda HVPE [Articol](CEP USM, 2018) Raevschi, Simion; Spalatu, Nicolae; Botnariuc, Vasile; Gorceac, Leonid; Potlog, Tamara; Dobromir, MariusPrin metoda reacțiilor chimice de transport HVPE (Hydride Vapor Phase Epitaxy) in sistemul (H2-NH3-HCl-Al-GaSi) au fost sintetizate straturi subțiri de AlN, AlGaN, GaN pe substraturi de siliciu, Si(111). Morfologia suprafeței, precum și a secțiunilor transversale ale structurilor a fost cercetată prin metoda SEM (Scanning Electron Microscopy) de rezoluție înaltă. Compoziția în secțiune transversală a structurilor a fost studiată prin metoda XRD (X-Ray Diffraction method), iar de suprafață – prin metoda XPS (X-Ray Photoelectronic Spectroscopy). Afară de aluminiu, galiu și azot în straturi au fost depistate oxigen și carbon. S-a stabilit că concentrația oxigenului pe suprafața straturilor de GaN, depuse la temperaturi relativ mai joase, este mai mică. Se presupune că concentrația ridicată a oxigenului în straturi are loc în urma descompunerii cuarțului, din care este confecționat reactorul, la temperaturi ridicate. S-a constatat că încorporarea galiului în straturile de AlGaN este diminuată de fluxul precursorilor aluminiului. Prin aceasta se demonstrează că viteza reacțiilor chimice ale precursorilor azotului cu ale aluminiului este semnificativ mai mare decât cu ale galiului, ultimele fiind înlăturate din zona de depunere de fluxul gazului de transport.