National Institute Of Materials Physics - Romania

Publications

838 articles found

791. Investigation of trapping levels in standard, nitrogenated and oxygenated Si p-n junctions by thermally stimulated currents

Authors: Pintilie, I; Petre, D; Pintilie, L; Tivarus, C; Petris, M; Botila, T

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 309, DOI: 10.1016/S0168-9002(99)00845-1

The trapping levels induced in p-n Si junctions by irradiation with 24 GeV proton were investigated using Thermally Stimulated Currents (TSC) methods in the 90-300 K temperature range. Several trapping levels, with activation energies between 0.27 and 0.57 eV, were put into evidence. The spatial distribution of the traps was investigated using different wavelengths for the light used to fill the traps. The results lead to the conclusion that the deepest trapping levels are not uniformly distributed in the volume of the sample. For the most important trapping level the average introduction rate was estimated to 0.9-1.2 cm(-1). The activation energy and the capture cross-section of this trapping level seems to depend on the impurity element introduced in Si. (C) 2000 Elsevier Science B.V. All rights reserved.

792. Experimental evidence of deep electron and hole trapping levels in high fluence proton irradiated p-n Si junctions using optical charging spectroscopy

Authors: Pintilie, I; Tivarus, C; Botila, T; Petre, D; Pintilie, L

Published: JAN 11 2000, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 439, 227, DOI: 10.1016/S0168-9002(99)00887-6

Optical charging spectroscopy (OCS) is first time reported as applied to p-n junctions. The existence of one deep trapping level for electrons and two deep trapping levels for holes was put into evidence, using this method, in proton irradiated p(+)-n-n(+) silicon structures. An analytical formula for the OCS discharging current for this type of structures was deduced. (C) 2000 Elsevier Science B.V. All rights reserved.

793. Influence of Bi and Y additions on the electromechanical anisotropy of lead titanate ceramics

Authors: Amarande, L; Tanasoiu, C; Miclea, C; Miclea, CF

Published: 2000, PIEZOELECTRIC MATERIALS: ADVANCES IN SCIENCE, TECHNOLOGY AND APPLICATIONS, 76, 66, DOI:

Lead titanate (PT) is well known as a good piezoelectric material with a high Curie temperature (similar to 490 degreesC) and a low dielectric constant (similar to 200). But pure lead titanate cannot be sintered as ceramic bodies, for practical purposes, due to its large crystal anisotropy (tetragonality c/a=1.064). However, dense PT ceramic bodies can be obtained if small additions of other elements are used. Ca and Sm modified PT were succesfully tried, but such dopings proved rather expensive for mass production. Therefore some other doping elements must be tried. In this regard we investigated the effect of Bi and Y additives on the piezoelectric properties of PT ceramics. The general formula of our Bi, Y doped lead titanate ceramics was: (Pb1-3x/2Mex)(Ti0,98Mn0,02)O-3, with Me=Bi,Y and x=0.04, 0.06, 0.08. The modified PT ceramics were prepared by conventional ceramic technique, using p.a.purity raw materials. The mixed powders were sintered at temperatures between 1000-1300 degreesC. Poling was done in fields of about 70kV/cm. Density and coupling factors of the samples were determined as a function of sintering temperatures, and doping level. Temperature dependence of the main piezoelectric characteristics was also investigated for temperatures as high as 500 degreesC. It was found that Bi,Y modified lead titanate ceramics have a very high Curie point (T-c>450 degreesC), a low dielectric constant (<140) and a large electromechanical anisotropy (the radial mode is nearly inexistent, at room temperature and the thickness coupling factor is about 0.4), which make them competitive to the rare-earth doped PT ceramics, for high temperature and high frequency transducers applications.

794. Piezoelectric properties of tungsten doped PZT type materials

Authors: Dimitriu, E; Ramer, R; Miclea, C; Tanasoiu, C

Published: 2000, FERROELECTRICS, 241, 213, DOI: 10.1080/00150190008224993

Piezoelectric properties of four tungsten doped samples of PZT type were determined as a function of composition. The samples were prepared by the usual ceramic technique from raw oxide of 99.9% purity. All compositions exhibited maximum values for the density at a sintering temperature of 1180 degrees C with a soaking time of 4h, so that the piezoelectric properties were determined on the samples sintered at this temperature only. The results showed that the piezoelectric properties were not drastically modified by the doping level, but dopings higher than 5% at. sightly alter the properties. The best values obtained for the piezoelectric parameters were: density rho= 7.7 g/cm(3); dielectric constants, epsilon(T)=1410; electromechanical coupling factors, k(p) = 0.63, and k(T) = 0.55; mechanical quality factor Q(m) approximate to 90; piezoelectric voltage constant d(33) = 470.10(-12) m/V; piezoelectric charge constant g33 = 25.10(-3) Vm/N. These values show that tungsten doped materials are piezoelectric soft type ceramics of high quality that can be successfully used for manufacturing ultrasonic transducers.

795. The influence of interface on the spontaneous polarisation in PbTiO3 thin films deposited on a silicon substrate

Authors: Boerasu, I; Pintilie, L

Published: 2000, PIEZOELECTRIC MATERIALS: ADVANCES IN SCIENCE, TECHNOLOGY AND APPLICATIONS, 76, 308, DOI:

Metal/ Ferroelectric/ Semiconductor (MFS) heterostructures have been of interest in the last decade due to possibility of their potential integration in classical silicon technology and because their potential use in memory devices. Research in this field has lead to new generations of sensors and actuators, laser modulators and deflectors, non-volatile random access memories (NRAM's). Unfortunately many at these types of devices remain in the prototype phase because of the impossibility to know and control phenomena which appear at the ferroelectric/ semiconductor interface. The present paper presents some results on the investigation of a PbTiO3/ Si heterostructure. A study of the film occurring at the interface and how it influences the ferroelectric properties of the heterostructure can clarify some problems of the reproducibility of the parameters of a MFS heterostructure.

796. Preparation and ferroelectric properties of graded Pb(TiXZr1-X)O-3 thin films

Authors: Boerasu, I; Pintilie, L; Matei, I; Pintilie, I

Published: 2000, 2000 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, CAS 2000 PROCEEDINGS, 448, DOI:

Pb(ZrxTil .x)O-3 (x = 0 divided by 0.8) graded thin films were fabricated by sol-gel method on Pt/ SiO2/ Si substrates using metal alkoxide solution. The samples were crystallized by conventional thermal annealing in air for 30 min. at 700 degreesC. The ferroelectric properties of the graded structure were investigated Specific unusual behavior in the ferroelectric loops like large offset on the polarization axis was observed and disscused.

797. The influence of cadmium salt anion on the growth mechanism and on the physical properties of CdS thin films

Authors: Pentia, E; Pintilie, L; Pintilie, I; Botila, T

Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 601, DOI:

Cadmium sulphide films were prepared by Chemical Bath Deposition (CBD) technique from CdCl2, CdSO4, Cd(CH3COO)(2) respectively, as cadmium precursor salts, and thiourea in ammoniacal medium. In this paper we study the changes in the morphology and properties of the films prepared from different cadmium salts, although the starting reaction parameters as concentration of the reactants, pH (denoted as pH(i)), temperature, and time of reaction for all precursor cadmium salts are identical. It is proposed that, during the deposition process, depending upon the anion type of cadmium salt the pH of reaction mixture decrease with different rates. The pH(i) decreases in the deposition bath could allow the change of the layers growth mechanism and therefore the change in the morphology and properties of the films. Above a certain value of starting pH (pH(i) >12.5), the pH decrease did not affect the growth mechanism and properties of the layers. The structure and morphology of the films were investigated by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). Also the optical, electrical and photoelectrical characteristics of the layers and their dependence on films morphology were presented. These studies have allowed us to establish the optimum conditions for fabrication of quality CdS films using CdCl2, CdSO4, or Cd(CH3COO)(2) as cadmium precursor salts.

798. Some annealing effects in proton irradiated silicon detectors

Authors: Pintilie, I; Petris, M; Tivarus, C; Moll, M; Fretwurst, E; Lindstroem, G

Published: 2000, 2000 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, CAS 2000 PROCEEDINGS, 262, DOI:

Annealing studies of a proton irradiated Si test diode (1MeV- neutron equivalent fluence is phi (eq) = 1.82x10(13) cm(-2)) were performed. The macroscopic characterization shows that during the annealing experiment the type inversion effect happened. The changes in the microscopic features during the annealing treatment were investigated using Thermally Stimulated Current method.

799. Trap characterization for Bi4Ti3O12 thin films by thermally stimulated currents

Authors: Pintilie, L; Pintilie, I; Petre, D; Botila, T; Alexe, M

Published: JUL 1999, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 69, 109, DOI: 10.1007/s003390050980

Thermally stimulated current (TSC) measurements performed in the 100 K-400 K temperature range on Bi4Ti3O12 (BiT) thin films annealed at 550 degrees C and 700 degrees C had revealed two trapping levels having activation energies of 0.55 eV and 0.6 eV. The total trap concentration was estimated at 10(15) cm(-3) for the samples annealed at 550 degrees C and 3 x 10(15) cm(-3) for a 700 degrees C annealing and the trap capture cross-section was estimated about 10(-18) cm(2). From the temperature dependence of the dark current in the temperature range 20 degrees C-120 degrees C the conduction mechanism activation energy was found to be about 0.956-0.978 eV. The electrical conductivity depends not only on the sample annealing temperature but also whether the measurement is performed in vacuum or air. The results on the dark conductivity are discussed considering the influence of oxygen atoms and oxygen vacancies.

800. Effect of small amounts of lead oxide on the piezoelectric properties of soft-type PZT ceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF

Published: JUN 1999, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 1, 65, DOI:

Soft type piezoceramics with stoichiometric composition Pb(Nb0.02Li0.007Zr0.51Ti0.463)O-3 were prepared by the usual ceramic technique. Several samples with lead oxide in excess of up to 4% wt, were prepared. Careful measurements of the density of the sintered disc-shaped materials and the piezoelectric properties (piezoelectric voltage constant, g(31), piezoelectric strain constant, d(31), dielectric permittivity,epsilon(r), electromechanical planar coupling coefficient, k(p), mechanical quality factor, Q(m)) were carried out. All piezoelectric properties were spectacularly enhanced by addition of small amount of lead oxide. The maximum values were reached for samples containing 2-3 wt.% PbO, regardless the sintering temperature. The experimental results were discussed in terms of the two competitive processes: structural rearrangement and dissolution-reprecipitation, which are active in the sintering process in the presence on the excess PbO liquid phase. The last process seems to be dominant and explains the improvement on the piezoelectric properties of PZT materials.