National Institute Of Materials Physics - Romania

Publications

858 articles found

791. Trapping levels in nanocrystalline porous silicon

Authors: Ciurea, ML; Draghici, M; Lazanu, S; Iancu, V; Nassiopoulou, A; Ioannou, V; Tsakiri, V

Published: MAY 22 2000, APPLIED PHYSICS LETTERS, 76, 3069, DOI: 10.1063/1.126581

Trapping levels in fresh (one month) and naturally aged (one year) nanocrystalline porous silicon have been investigated using the optical charging spectroscopy method. Four significant maxima and/or shoulders were observed for fresh samples and five for aged ones. They have been attributed to five and six trapping levels, respectively. The trapping centers corresponding to the most shallow four levels are situated at or nearby the internal surface of the porous silicon films. (C) 2000 American Institute of Physics. [S0003-6951(00)01621-1].

792. Electrical and photovoltaic properties of photosensitised ITO/a-Si : H p-i-n/TPyP/Au cells

Authors: Antohe, S; Ion, L; Tomozeiu, N; Stoica, T; Barna, E

Published: MAY 15 2000, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 62, 216, DOI: 10.1016/S0927-0248(99)00127-0

The a-Si:H p-i-n photovoltaic cells photosensitized with an organic layer of 5,10,15,20-tetra (4-pyrydil) 21H,23H porphine (TPyP) have been prepared. The action spectrum of these cells was extended by approximately 30 nm to longer wavelengths, with respect to non-sensitized cells. The presence of the organic layer gives some modifications in the electrical and photovoltaic behavior of the cells, that is why an analysis of dark current-voltage characteristics of the cells at room temperature, is also presented. (C) 2000 Elsevier Science B.V. All rights reserved.

793. Size distribution and electroluminescence of self-assembled Ge dots

Authors: Vescan, L; Stoica, T; Chretien, O; Goryll, M; Mateeva, E; Muck, A

Published: MAY 15 2000, JOURNAL OF APPLIED PHYSICS, 87, 7282, DOI: 10.1063/1.372980

In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small (pyramids) and larger (dome) islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns. (C) 2000 American Institute of Physics. [S0021-8979(00)04610-7].

794. Electron-hole recombination in PbCl2 : T1 crystals

Authors: Nistor, SV; Stefan, M; Goovaerts, E; Schoemaker, D

Published: MAY 2000, JOURNAL OF LUMINESCENCE, 87-9, 551, DOI: 10.1016/S0022-2313(99)00287-2

A correlated ESR and optical emission study on samples doped with different concentrations of Tl+ impurity ions shows the involvement of paramagnetic Pb-2(3+) self-trapped electron centers (STEL) and trapped hole A centers in the electron-hole recombination responsible for the 2.6 eV blue-green luminescence. (C) 2000 Elsevier Science B.V. All rights reserved.

795. Structural investigation of a La0.6Y0.07Ca0.33MnO3 thin film by high resolution transmission electron microscopy

Authors: Ghica, C; Nistor, LC; Teodorescu, VS; Valeanu, M; Ristoscu, C; Mihailescu, IN; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 72, DOI:

The morphology and structure of a La0.6Y0.07Ca0.33MnO3 thin film is studied by transmission electron microscopy. The film was grown by pulsed laser deposition (PLD) on an MgO-buffered silicon <100> wafer. The as-deposited films are polycrystalline and show a columnar morphology. We present a detailed high-resolution transmission electron microscopy structural study concerning a possible monoclinic distortion of the orthorhombic LYCMO crystal cell. (Received February 22, 2000; accepted March 10, 2000).

796. Structural comparison between La0.60Y0.07Ca0.33MnO3-delta bulk and pulsed laser deposited thin films

Authors: Teodorescu, VS; Nistor, LC; Valeanu, M; Ghica, C; Sandu, C; Mihailescu, IN; Ristoscu, C; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 211, 60, DOI: 10.1016/S0304-8853(99)00713-1

This work is a comparative study of the structural and magneto-transport properties of La0.60Y0.07Ca0.33MnO3-delta (LYCMO) as bulk and thin film. The bulk samples were prepared by solid-state reaction between the corresponding metallic oxides mixed in stoichiometric ratios. The thin film was deposited by pulsed laser deposition on an MgO single crystal using an excimer laser. We show that the structure and stoichiometry of the bulk target are perfectly reproduced in the thin film. We measured the magnetoresistive effect on both the LYCMO pellet and the thin film by using the four-probe technique. The maximum of the MR effect is 680% on the polycrystalline thin film in a 2T magnetic field. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

797. Optical characterization of dielectric borophosphosilicate glass

Authors: Gartner, M; Modreanu, M; Bosch, S; Stoica, T

Published: APR-MAY 2000, MICROELECTRONICS RELIABILITY, 40, 620, DOI: 10.1016/S0026-2714(99)00291-7

Atmospheric pressure chemical vapour deposition films of borophosphosilicate glass with different contents of phosphorus and boron can be successfully used as masks for etching of silicon in KOH solution. The optical properties of these films were pointed out by spectroellipsometric measurements, using different theoretical models (such as Cauchy and Wemple-DiDomenico models). (C) 2000 Elsevier Science Ltd. All rights reserved.

798. EPR observation of first point defects in cubic boron nitride crystalline powders

Authors: Nistor, SV; Stefan, M; Schoemaker, D; Dinca, G

Published: 2000, SOLID STATE COMMUNICATIONS, 115, 44, DOI: 10.1016/S0038-1098(00)00135-6

An X-band electron paramagnetic resonance (EPR) study of nominally pure, diamond-like cubic boron nitride (c-BN) crystalline powders, has led to the first identification of a spectrum attributed to two related paramagnetic species. The composite EPR spectrum can be observed only in dark brown colored powders known to contain excess of boron. It consists of two superimposed lorentzian components, called D1 and D2, centered at g1 = 2.0063 and g2 = 2.0084, with peak-to-peak linewidths of 3.3 and 17.9 mT, respectively. The temperature dependence of the integrated intensities, their linewidths and intensity ratio D2/D1 allows one to conclude that the narrow line D1 originates from EPR transitions inside a S = 1/2 ground doublet and the broad line D2 from transitions inside the excited levels of another center. Evidence suggests that both centers are boron related paramagnetic species. (C) 2000 Elsevier Science Ltd. All rights reserved.

799. Electrical properties of nanocrystalline porous silicon

Authors: Ciurea, ML; Iancu, V

Published: 2000, 2000 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, CAS 2000 PROCEEDINGS, 64, DOI: 10.1109/SMICND.2000.890188

Conduction properties as well as trapping phenomena in nanocrystalline porous silicon films are investigated in relation to their microstructure. Theoretical models to describe the phenomena are proposed. The main results presented in this paper are: the two-scale porosity of our porous silicon films, the decisive role of the quantum confinement to the conduction phenomena and the prominent part played by the oxidation on the surface effects.

800. Characterization of ITO thin films prepared by spinning deposition starting from a sol-gel process

Authors: Stoica, TF; Stoica, TA; Zaharescu, M; Popescu, M; Sava, F; Popescu-Pogrion, N; Frunza, L

Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 688, DOI:

ITO thin films were deposited by spin coating method starting from indium and tin propoxide in the frame of a sol-gel process. Films with the thickness corresponding to 68 nm for one layer deposition were produced and characterized by X-ray diffraction, transmission electron microscopy and infrared reflection spectroscopy. Low conductivity polycrystalline films exhibiting cubical structure (bixbyite-type) and good adherence were obtained.