National Institute Of Materials Physics - Romania

Publications

849 articles found

761. Bulk damage effects in standard and oxygen-enriched silicon detectors induced by Co-60-gamma radiation

Authors: Fretwurst, E; Lindstrom, G; Stahl, J; Pintilie, I; Li, Z; Kierstead, J; Verbitskaya, E; Roder, R

Published: NOV 21 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 514, 8, DOI: 10.1016/j.nima.2003.08.077

The influence of oxygen in silicon on bulk damage effects induced by Co-60-gamma irradiation has been studied in a dose range between 0.2 and 900 Mrad. The detector processing and oxygen enrichment were carried out in a common project by the Institute of Micro-sensors CiS using n-type high-resistivity FZ silicon (3-6 kOmega cm) with <111> and <100> orientation. Different oxygen concentrations were achieved by diffusion at 1150degreesC for 24, 48 and 72 h. This report on bulk damage effects is focussed on the observed changes in the reverse current, the effective space charge density N-eff extracted from C/V measurements and investigations using the transient current technique. A substantial improvement of radiation hardness concerning the development of the macroscopic properties was found for detectors manufactured on oxygenated material compared to standard material. It will be demonstrated that the change of the effective space charge density as well as the increase of the reverse current can be attributed to the creation of two deep acceptor levels and a shallow donor level. (C) 2003 Elsevier B.V. All rights reserved.

762. Results on defects induced by Co-60 gamma irradiation in standard and oxygen-enriched silicon

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: NOV 21 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 514, 24, DOI: 10.1016/j.nima.2003.08.079

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of Co-60 gamma irradiation, using Deep Level Transient Fourier Spectroscopy and Thermally Stimulated Current methods. The main focus was on differences between standard and oxygen-enriched material and the impact of the observed defect generation on the diode properties. Two close to mid gap trapping levels and a bi-stable donor level have been found to be responsible for the main macroscopic changes both in standard and oxygen-enriched float zone diodes. (C) 2003 Elsevier B.V. All rights reserved.

763. Second-order generation of point defects in gamma-irradiated float-zone silicon, an explanation for 'type inversion' (vol 82, pg 2169, 2003)

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: OCT 13 2003, APPLIED PHYSICS LETTERS, 83, 3216, DOI: 10.1063/1.1619226

764. Deep defect levels in standard and oxygen enriched silicon detectors before and after Co-60-gamma-irradiation

Authors: Stahl, J; Fretwurst, E; Lindstrom, G; Pintilie, I

Published: OCT 11 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 512, 116, DOI: 10.1016/S0168-9002(03)01884-9

Capacitance Deep Level Transient Spectroscopy (C-DLTS) measurements have been performed on standard and oxygen-doped silicon detectors manufactured from high-resistivity n-type float zone material with <111> and < 100> orientation. Three different oxygen concentrations were achieved by the so-called diffusion oxygenated float zone (DOFZ) process initiated by the CERN-RD48 (ROSE) collaboration. Before the irradiation a material characterization has been performed. In contrast to radiation damage by neutrons or high-energy charged hadrons, were the bulk damage is dominated by a mixture of clusters and point defects, the bulk damage caused by Co-60-gamma-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after Co-60-gamma-irradiation by C-DLTS are the electron traps VOi, CiCs, V-2(=/-), V-2(-/0) and the hole trap CiOi. The main difference between standard and oxygenated silicon at low dose values can be seen in the introduction rate of CiCs compared to CiOi. For highly oxygenated silicon the introduction of CiCs is fully suppressed, while the sum of the introduction rates g(CiCs)+g(CiOi) is independent on the oxygen concentration. (C) 2003 Elsevier B.V. All rights reserved.

765. Growth and properties of Pb(ZrxTi1-x)O-3 step graded-structures

Authors: Boerasu, I; Pintilie, L; Pereira, M; Gomes, MJM; Vilarinho, PM

Published: SEP 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 775, DOI:

Pb(Zr-x Ti1-x)O-3 (x = 55, 65, 92), PZT step graded-structure have been deposited by sol-gel technique on Pt-coated Si. Up-graded and down-graded structures has been obtained by changing the Zr/Ti ratio in steps a long to the film thickness. Up means that the ratio was increased from the bottom to the top while down means it was decreased. The properties of these films were investigated and compared with those of conventional films with homogeneous composition. It was found that the properties of up and down graded structures are completely different. Up-graded films have better ferroelectric properties than the downgraded ones. Pyroelectric signal could be detected also on as-grown up-graded films, in accordance with the structural results that show a strong (100) orientation in this case, The coercive field of the up-graded film is lower than the values obtained in case of homogeneous films with the same Zr/Ti ratios like those used in the graded structures.

766. Bi influence on growth and physical properties of chemical deposited PbS films

Authors: Pentia, E; Pintilie, L; Botila, T; Pintilie, I; Chaparro, A; Maffiotte, C

Published: JUN 23 2003, THIN SOLID FILMS, 434, 170, DOI: 10.1016/S0040-6090(03)00449-8

PbS films were chemically deposited on glass substrates from chemical reducing bath doped with Bi. The growth and properties of PbS layers are investigated. The effect of the reducer and Bi3+ ions on the deposition process was studied with a quartz-crystal microbalance technique. The reducer introduces a new deposition mechanism of electrochemical nature, which allows for thicker films. On the other hand, Bi3+ ions introduce nucleation centers in the solution (Bi(OH)(3)), which accelerate the homogeneous precipitation and diminish the film thickness. The PbS grain size within the layer increases with increasing the Bi content in the deposition bath. A considerable enhancement of the photoconductive signal was found in case of PbS films deposited from Bi doped bath. The signal has nonlinear behavior with the Bi content in the chemical bath. There is an optimum quantity of Bi for which the photoconductive characteristic reaches maximum. (C) 2003 Elsevier Science B.V. All rights reserved.

767. Simple model of polarization offset of graded ferroelectric structures

Authors: Pintilie, L; Boerasu, I; Gomes, MJM

Published: JUN 15 2003, JOURNAL OF APPLIED PHYSICS, 93, 9967, DOI: 10.1063/1.1577401

The abnormal polarization offset observed in case of graded ferroelectric structures is explained assuming the presence of a nonreversible part of polarization due to the imposed polarization gradient. It is shown that an upper limit for the offset should exist, fixed by the remnant polarization of the component materials considered as independent layers. This is valid for the structures in which polarization increases or decreases in steps from one layer to the other, but should also be valid for the structures with continuous gradient. However, large values of the charge offset could be achieved in the last case. The electric field dependence of the polarization offset is predicted, together with the possibility of obtaining large nonconventional pyroelectric coefficients. The simulation developed in the case of a bilayer ferroelectric structure and using data from the lead-lanthanum-zirconate-titanate system describes well the observed features of the graded ferroelectric structures. (C) 2003 American Institute of Physics.

768. Combined chemical-physical methods for enhancing IR photoconductive properties of PbS thin films

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

Published: JUN 2003, INFRARED PHYSICS & TECHNOLOGY, 44, 211, DOI: 10.1016/S1350-4495(02)00225-6

IR photoconductive properties of PbS films can be controlled using two different methods: (1) chemical, controlling the film morphology and, thus, the physical film properties by adding small amounts of impurities in the deposition bath, (2) physical, using field effect in complex PbS/SiO2/Si pseudo-MOS structures to control the photoconductivity of PbS film. (C) 2003 Elsevier Science B.V. All rights reserved.

769. Iterative evaluation of the complex constants of piezoceramic resonators in the thickness mode

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

Published: JUN 2003, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 23, 1145, DOI: 10.1016/S0955-2219(02)00277-7

An iterative method is presented for the characterization of lossy piezoelectric materials in the thickness resonant mode, which allows to calculate the frequencies at which the electrical impedance is to be measured. This new method considerably reduces the measurement time by separating the programs for data acquisition and for processing thus simplifying the measurement procedure. The accuracy of the method was tested for several piezoceramic materials, covering a wide range of values of the thickness coupling factor and mechanical quality factor. The new method proved to be as accurate as other iterative methods, but it is easier to apply. (C) 2002 Elsevier Science Ltd. All rights reserved.

770. Competition between ferroelectric and semiconductor properties in Pb(Zr0.65Ti0.35)O-3 thin films deposited by sol-gel

Authors: Boerasu, I; Pintilie, L; Pereira, M; Vasilevskiy, MI; Gomes, MJM

Published: APR 15 2003, JOURNAL OF APPLIED PHYSICS, 93, 4783, DOI: 10.1063/1.1562009

Asymmetric metal-ferroelectric-metal (MFM) structures were manufactured by sol-gel deposition of a lead zirconate-titanate (PZT with Zr/Ti ratio 65/35) film on Pt-coated Si, with a Au top electrode. The average remnant polarization of 9 muC/cm2 and the coercive field of 39 kV/cm were obtained from the hysteresis loop measurements. A detailed analysis of the polarization-electric field (P-E), capacitance-voltage (C-V), and current-voltage (I-V) measurement results allowed us to estimate the near-electrode space-charge region thickness (roughly half of the film thickness at zero voltage), net doping concentration (around 10(18) cm(-3)), built-in potential (in the 0.4-0.8 V range, depending on the injecting electrode), and dynamic dielectric constant (5.2). The current logarithm-voltage dependence for the field-enhanced Schottky emission obeys a "1/4" law. The spectral distribution of the short circuit current measured under continuous light illumination in the 290-800 nm range exhibits a cutoff wavelength at 370 nm and a maximum sensitivity at about 340 nm. The estimated band-gap energy of the PZT material is 3.35 eV. The MFM structure is discussed in terms of two back-to-back Schottky diodes with a ferroelectric material in between. It is concluded that the semiconductor properties of the films are not negligible and, in certain conditions, are dominating over the ferroelectric ones. (C) 2003 American Institute of Physics.