Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering

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Epitaxial relations in BaF2 films grown by MBE on Si(III) substrates [Articol]
(Institute of Electrical and Electronics Engineers Inc., 1995-10-11) Belenciuc, Alexandr; Fiodorov, Alexandr; Zencenco, Vladimir; Lucaș, Victor; Vasiliev, Alexandr
The 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.
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, Petru
CdS 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.
Non-linear transport properties of PbTe(Ga) semiconductors [Articol]
(Institute of Electrical and Electronics Engineers Inc., 1997-10-07) Nicorici, Andrei; Canțer, Valeriu; Nicorici, Valentina; Constantinescu, Dana
The 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.
The structure of high-temperature blue luminescence centers in zinc selenide and mechanisms of this luminescence [Articol]
(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.
Nuclear quadrupole resonance of mixed-valence charge-ordered dimers [Articol]
(1999) Clochișner, Sofia; Gorceac, Leonid
The 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.
On the photoconductivity of Bi2O3 in thin films [Articol]
(2000) Leontie, Liviu; Caraman, Mihail; Rusu, Gheorghe Ioan
The 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.
Hot wall beam epitaxial growth of PbTe layers on BaFdCaFdSi(llI) substrates [Articol]
(Institute of Electrical and Electronics Engineers Inc., 2000-10-10) Belenciuc, Alexandr
PbTe(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.
Hartree-fock Semiconductor Bloch Equations and charge density correlations [Articol]
(2002) Klyukanov, Alexandr; Loiko, Natalia; Babushkin, Ihar; Gurau, Virginia
Generalized 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].
Probleme propuse la Olimpiada Republicană de Fizică – 2003 [Articol]
(2003) Evtodiev, Igor; Cliucanov, Alexandr; Cojuhari, Dumitru; Andronic, Iuliana
Concursul rezolvitorilor [Articol]
(2003) Catană, Pavel; Cârlig, Sergiu; Cliucanov, Alexandr; Marinciuc, Mihai; Miglei, Mircea; Potlog, Miron; Sîrghi, Anatol
Giant negative photoconductivity in La0.7Ca 0.3MnO3 thin films [Articol]
(2004) Moșneaga, Vasilii; Giske, Arnold; Samwer, Konrad; Mișina, Elena; Tamura, Takehisa; Nakabayashi, Seiichiro; Belenciuc, Alexandr; Șapoval, Oleg; Culiuc, Leonid
The 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.
Thermal and dielectric studies of 2,2’-dihydroxybenzophenone [Articol]
(Akadémiai Kiadó, 2005) Tomitaka, S.; Mizukami, M.; Paladi, Florentin; Oguni, M.
Thermal and dielectric properties of 2,2’-dihydroxybenzophenone were studied in relation with the potential progress of crystal nucleation and growth below the ordinary glass transition temperature, Tgα. Differential scanning calorimetry was carried out in a range 100-350 K. The α glass transition was found to occur at Tgα=239 K. Crystallization and fusion were observed to take place when the sample was cooled down to 103 K, but not observed when cooled to 203 K. Crystal nucleation was interpreted as having happened during annealing for a short time at 103 K which is much below the Tgα. Heat capacities were measured in a range 7-350 K by an intermittent heating method with an adiabatic calorimeter. The temperature, enthalpy and entropy of fusion were determined to be 334.46 K, 20.07 kJ mol-1 and 60.01 J K-1mol-1, respectively. Crystal growth was found to proceed even at 220 K below the Tgα, but no glass transition was detected below 220 K. Dielectric losses were measured in a temperature range of 100-250 K and a frequency range of 30Hz-10 kHz. β-Relaxation process was found dielectrically with the activation energy of 22.6 kJ mol-1, and the corresponding glass transition was expected to occur at 76.9 K. It is discussed, based on the “structurally ordered clusters aggregation” model for supercooled liquids and glasses, that the β process is potentially attributed to the crystal nucleation progressing at 103 K.
Kinetics of photoconductivity and photoluminescence of CdS/CdTe heterojunctions [Articol]
(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.
Gallium arsenate removal from waste waters [Articol]
(2005) Baranov, Serghei; Cinic, Boris; Redwing, Joan; Stăvilă, Vitalie
The 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.
On the photomagnetic effect in CdTe thin films evaporated onto unheated substrates [Articol]
(2005) Rusu, George G.; Rusu, Mihaela; Caraman, Mihail
Cadmium telluride (CdTe) thin films (d=500–700 nm) were deposited onto unheated glass substrates by thermal evaporation under vacuum. The dependence of the photomagnetic voltage on the magnetic induction for the as deposited and heat-treated films was investigated. The spectral dependence of the photomagnetic voltage was also investigated. The results are discussed in relation with structural characteristics of the studied films.
Electrical and photoelectrical properties of heterojunctions on the base of Cu(InGa)Se2 [Articol]
(2005) Chetruș, Petru; Gașin, Petru; Nicorici, Valentina; Suman, Victor
CdS films deposited by hot wall technique on mica were used as substrates for Cu(InGa)Se2 deposition. Two methods were used for the deposition of Cu(InGa)Se2 films: a) vacuum thermal evaporation from a single source and b) “flash” evaporation. The obtained films were of p-type conductivity with hole concentration varied from 2×1018 cm-3 to 6×1020 cm-3 depending on the fabrication method. The structures Cu(InGa)Se2–CdS were divided into two groups: the structures of type I having the CdS film thickness from 1.6 m to 2.8 m and the structures of type II having the CdS film thickness from 0.6 m to 0.8 m. It was established that the direct/reverse current ratio is 8-16. For the first type heterostructures the diffusion potential is 1.2–1.8 V and for the second type is 0.2–0.34 V. The Cu(InGa)Se2–CdS fotosensitivity is situated in the wavelength region from 0.51 m to 1.1 m and is determined by the electron-hole pair generation in both materials.
Method of study gallium and arsenic losses in technology of gallium arsenate obtained from wastes [Articol]
(2005) Baranov, Serghei; Redwing, Joan; Bogdevici, Oleg; Cinic, Boris; Izmailov, Denis
Having 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.
Converter of x-ray radiation on the basis of A 2B 6 - Layers, obtained by a method chemical pulverization [Articol]
(SPIE, 2005) Goglidze, Tatiana; Dementiev, Igor; Cortiucova, Iulia; Mațcova, Natalia
Multiplasmon laser gain spectra of quantum wells [Articol]
(2005) Klyukanov, Alexandr; Gurau, Virginia
Results of computer simulations concerning gain spectra of In0.05Ga0.95As quantum wells are presented. A novel multi-plasmon concept of a light absorption and laser gain of low- dimensional structures is comprehensively discussed. A generalized theory of multi-plasmon optical transitions in direct gap quantum wells is developed using the cumulant expansion method and fluctuation-dissipation theorem. Multi-quantum LO-phonon-plasmon optical transitions are investigated with account on coherent memory effects in quantum wells. It is shown that a red shift of the absorption edge can be caused not only by the well-known mechanism of band gap shrinkage but also by multi-plasmon transitions. The comparison with other theories and experimental data measured in In0.05Ga0.95As quantum wells is given.
Development of dissipative structures on surface of dielectric liquid in electrostatic field [Articol]
(2005) Constntinov, Boris; Bocan, V.; Pasechnic, Teodosie; Untila, Pantelei
The transition of plane surface of liquid dielectric charged with the electrical charge in the electrostatic field in the periodical gofer surface of crater type deformation is researched. It was proved for the first time that the apparition of dissipative structures keeps not optical character but thermal and is not conditioned by the presence of the photo sensible semiconductor layer. It was esta blished that the development of dissipative structures on the surface of dielectric liquid includes in itself the mechanism of initiation of germination deformations and a mechanism of multiplication of the centers of new deformations in the free volume of germination deformation.