2. Articole
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Item EPITAXIAL RELATIONS IN BaF2 FILMS GROWN BY MBE ON Si(III) SUBSTRATES(Institute of Electrical and Electronics Engineers Inc., 1995-10-11) Belenciuc, Alexandr; Fiodorov, Alexandr; Zencenco, Vladimir; Lucaș, Victor; Vasiliev, AlexandrThe dependence of the epitaxial orientations of the films in BaFdSi(III) heterostructures on growth conditions and the influence of heat treatment on the stability of epitaxial relations in such structures are investigated. The correlations between the types of epitaxial relations and structures of interface are also discussed.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 NON-LINEAR TRANSPORT PROPERTIES OF PbTe SEMICONDUCTORS(Institute of Electrical and Electronics Engineers Inc., 1997-10-07) Nicorici, Andrei; Canțer, Valeriu; Nicorici, Valentina; Constantinescu, DanaThe results of the I-V characteristics (IVC) investigation on PbTe〈Ga〉 semiconductor samples in the temperature range 67-100 K are given. IVC was found to be N-shaped, and at temperatures below 77 K the electric current oscillations through the sample were observed.Item THE STRUCTURE OF HIGH-TEMPERATURE BLUE LUMINESCENCE CENTERS IN ZINC SELENIDE AND MECHANISMS OF THIS LUMINESCENCE(Springer Nature, 1998) Ivanova, G.N.; Kasiyan, V.A.; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Simashkevich, A.V.The characteristic features of temperature quenching of the intensity of the edge luminescence bands of n-ZnSe crystals annealed in different media (vacuum, Zn, Se) are investigated a wide temperature range. A change in the mechanisms of high-temperature exciton luminescence in the short-wavelength region of the spectrum (443 nm) with increase in temperature of the crystal is observed. It is shown that the nature of temperature quenching of the long-wavelength edge luminescence band (458 nm) is evidence of dissociation of associative luminescence centers with increase in the sample temperature.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 ON THE PHOTOCONDUCTIVITY OF Bi2 O3 IN THIN FILMS(2000) Leontie, Liviu; Caraman, Mihail; Rusu, Gheorghe IoanThe spectral characteristics of photoconductivity for Bi2 O3 thin films were investigated. The films were prepared by thermal oxidation in air of Bi evaporated films. As revealed by X-ray diffraction and polarizing microscopy studies, polycrystalline and multiphasic films were obtained. From the photoconductivity spectral curves, the bandgap energy values were determined, by using the Moss criterion. The influence of oxidation (preparation) conditions on the Eg values is discussed. The photoconductivity of Al-Bi 2 O3 -Al, Cu-Bi 2 O3 -Cu and Al- Bi 2 O3-In 2 O3 structures is also investigated.Item HOT WALL BEAM EPITAXIAL GROWTH OF PbTe LAYERS ON BaFdCaFdSi(llI) SUBSTRATES(Institute of Electrical and Electronics Engineers Inc., 2000-10-10) Belenciuc, AlexandrPbTe(III) thin films were grown by the hot wall beam epitaxy (HWBE) technique on Si( III ) substrates using intermediate BaF2/CaF2 buffers grown by MBE. The best PbTe layers exhibit the high resolution X-ray rocking curve linewidth of about 130 arcsec,the low temperature Hall mobility of 8 x l d cm2Ns, and an excellent surface morphology with the roughness of a few angstrom as it was determined by the atomic force microscopy (AFM). The results indicate that high-quality PbTe films can be obtained on fluoride covered Si(III ) substrates by simple and cheap HWBE method.Item HARTREE-FOCK SEMICONDUCTOR BLOCH EQUATIONS AND CHARGE DENSITY CORRELATIONS(2002) Klyukanov, Alexandr; Loiko, Natalia; Babushkin, Ihar; Gurau, VirginiaGeneralized Semiconducor Bloch Equations are derived with using the fluctuation-dissipation theorem. Four op- erator expectation values like density-density correlators are calculated with account of coherent memory effects. Interactionswith mixed plasmon-phonons modes and excitonic effects are taken into account. Comparison with different other theoretical approaches is provided. Numerical calculations of the spontaneous radiationproduced by interband multiplasmon recombination of electron-hole pairs are fulfilled in dependence on the temperatureand plasmaconcentration. It is shown that the intensity maximum of spontaneous radiationshifted to the region of the first LO-phonon satellite with increasing of concentration in accordance with experiments [19,21].Item CONCURSUL REZOLVITORILOR(2003) Catană, Pavel; Cârlig, Sergiu; Cliucanov, Alexandr; Marinciuc, Mihai; Miglei, Mircea; Potlog, Miron; Sîrghi, AnatolItem PROBLEME PROPUSE LA OLIMPIADA REPUBLICANĂ DE FIZICĂ – 2003(2003) Evtodiev, Igor; Cliucanov, Alexandr; Cojuhari, Dumitru; Andronic, IulianaItem GIANT NEGATIVE PHOTOCONDUCTIVITY IN La 0.7Ca0.3MnO3 THIN FILMS(2004) Moșneaga, Vasilii; Giske, Arnold; Samwer, Konrad; Mișina, Elena; Tamura, Takehisa; Nakabayashi, Seiichiro; Belenciuc, Alexandr; Șapoval, Oleg; Culiuc, LeonidThe increase of the resistance up to two orders of magnitude under laser illumination (l5760 nm) was observed in La0.7Ca0.3MnO3 ~LCMO! epitaxial thin films in ferromagnetic state.Optical absorption also increases by 10–15 % and the magnetic second-harmonic generation signal decreases down to zero under the irradiation. The light induced changes are reversible with decreases down to zero under the irradiation. The light induced changes are reversible with characteristic relaxation times t;1 – 30 s. Magnetic field, B54 T, suppresses the photoconductivity and decreases its relaxation time. Photoinduced effects are caused by the injection of a large number of extra carriers, which change the ~antiferromagnetic! AFM/FM phase balance in LCMO, favoring the insulating AFM state.Item INFLUENCE OF DEFECT COMPOSITION ON OPTICAL ACTIVITY OF Mn 2+ IONS IN ZnS CRYSTALS(2005) Korotkov, Vitalii; Sobolevskaya, Raisa; Bruk, Leonid; Sushkevich, Constantin; Ketrush, Petru; Dubrovin, A.The Mn Zn2+ ion intracentred luminescence in ZnS crystal (max=590nm, FWHM=160-210meV) and its relation to the native, impurity (the background and aluminum) defects formed at the crystal annealing in the bismuth melt at 950oC during 100hrs was studied. The luminescence of the aluminum doped and undoped ZnS single crystals , before and after annealing, were studied. The aluminum presence on the one hand creates sensitizing centers (the radiation bands close to 400nm and 450nm) and on the other hand makes difficult Mn doping of the crystal. It is supposed that the temperature influence on the Mn Zn2+ ion is determined by the position of the electron and hole Fermi cuazi-levels relative to the deep levels, acting as recombination radiative and noneradiative centers the nature of which is determined by the type of crystal lattice defects. The relation between blue centers of recombinative radiation and Mn bands was shownItem KINETICS OF PHOTOCONDUCTIVITY AND PHOTOLUMINESCENCE OF CdS/CdTe HETEROJUNCTIONS(2005) Vatavu, Sergiu; Caraman, Iuliana; Gashin, Peter A.The photoluminescence and absoption spectral distribution close to the edge of fundamental band were studied in the CdS and CdTe films components of the CdS/CdTe heterojunctions. Recombination level energetic position was determined. The annealing of the CdS/CdTe heterojunctions in presence of CdCl2 results in formation of new recombination levels, revealed by a luminescent band in the energy range of 1.6-1.7 eV and by the shift of the impurity band maximum to the red wavelength region by 50 meV.Item ELLIPSOMETRIC STUDIES OF NANOMETRIC CdS AND CdTe FILMS(2005) Caraman, Mihail; Evtodiev, Igor; Cuculescu, Elmira; Rusu, Marin; Salaoru, IurieThe thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analysis of the polarization ellipse of the reflected light from the surfaces of structures thin layers substrate. The thermal treatment of the samples CdS-CdTe in the presence of CdCl2 leads to the increasing of the crystalline phase from layers.Item MODELING OF TEMPERATURE REGIMES OF THIN FILM GAS SENSITIVE DEVICES(2005) Dmitriev, SergheiThis paper presents results of the modeling of the temperature distribution in a chip of thin film gas sensor, operating at high temperatures (150-1000 oC), required to provide high sensitivity and selectivity to target gases. Analysis of thermal regimes of such chip was carried out on the base of model of plate with local source of heat. It was found that substrate heat conductivity is most influencing parameter, determining both temperature distribution in chip and also the electrical power consumption decreasing. The example of realized chips designed in accordance with results of modeling is presented. The results of modeling are compared with experimental data.Item GALLIUM ARSENATE REMOVAL FROM WASTE WATERS(2005) Baranov, Serghei; Cinic, Boris; Redwing, Joan; Stăvilă, VitalieThe aim of this paper is to study the loss of gallium (Ga) and arsenic (As) loss during the sedimentation of gallium arsenate (GaAsO4 ) from waste solutions of GaAs epitaxial production by chloride method. The solid wastes of this semiconductor manufacturing process are removed from technological equipment by dissolution in an acidic etching solution. In order to recover valuable Ga and very toxic As from these waste solutions we proposed to precipitate them as gallium arsenate. Experiments have been conducted to determine the migration of the two elements in filtrate and washing solutions as a function of pH for both model and real industrial wastes. It has been determined the optimal interval of pH for sedimentation, the losses of Ga and As present 0,01-0,053%. For model solutions the sedimentation is optimal in the range of pH from 3,2 to 4,3, while in the case of real waste solution this interval is 3,6-5,0. Comparative evaluation of the precipitation efficiency revealed that for model solutions the arsenic loss during the precipitation is higher (0,5%), and this can be explained by a different ratio of initial Ga3+ and AsO43- in model and real solutions. The results described in this paper provide important guidelines for the sedimentation of gallium arsenate from acidic waste solutions and indicate an overall efficiency of the process that could lead to savings in cost and process time for industrial effluent treatment technologies.Item CONVERTER OF X-RAY RADIATION ON THE BASIS OF A2B6-LAYERS OBTAINED BY A METHOD OF CHEMICAL PULVERIZATION(SPIE, 2005) Goglidze, Tatiana; Dementiev, Igor; Cortiucova, Iulia; Mațcova, NataliaItem METHOD OF STUDY GALLIUM AND ARSENIC LOSSES IN TECHNOLOGY OF GALLIUM ARSENATE OBTAINED FROM WASTES(2005) Baranov, Serghei; Redwing, Joan; Bogdevici, Oleg; Cinic, Boris; Izmailov, DenisHaving the goal to recover gallium (Ga) and arsenic (As) from technological wastes derived from the process of growing epitaxial gallium arsenide structures, it is proposed to extract gallium arsenate (GaAsO4) by precipitation and filtration of the sediment. In this paper it is proposed to measure the concentrations of Ga and As by means of the atomic absorption spectrometer AAnalyst 800 directly in the filtrate solution. We compare the results obtained by two methods of elemental Ga and As atomization: flame and thermal atomization. The values of Ga and As concentrations in filtrate are function of pH for solutions containing 1- 680 mg/1 of Ga and 55-880 mg/1 of As. The developed method can be used to study and further optimize the technological process.Item OPTICAL PROPERTIES OF CRYSTALS GaSe AND InSe DOPED WITH Cu(2005) Evtodiev, Igor; Cuculescu, Elvira; Caraman, Mihail; Anghel, Sergiu; Petrov, M.The anisotropy of absorption spectra in the range of the margin of fundamental band of the crystals GaSe and InSe doped with Cu in the percentage quantities up to 0.5 % at. from which the implementation mechanism of the impurity atoms of Cu in the hexagonal crystal grating of the GaSe and InSe crystals and the localization energy of the impurity levels in the forbidden energetic band is studied.Item IMPURITY DISTRIBUTION IN n-ZnSe CRYSTALS DOPED WITH Au(2005) Nedeoglo, Dmitrii; Nedeoglo, Natalia; Sirkeli, VadimHall effect, electric conductivity and mobility of charge carriers in n-ZnSe single crystals doped with Au are investigated in the temperature range from 77 to 300 K. Impurity distribution in the crystals was studied by a method of “layer-by-layer” etching of a sample surface. The model, which explains this distribution by a simultaneous diffusion of Zn and Au atoms during a long-term high-temperature annealing of as-grown crystals in Zn + Au melt, is proposed.