National Institute Of Materials Physics - Romania

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885 articles found

851. Photoconductive properties of Bi4Ti3O12/Si heterostructures with different thickness of the Bi4Ti3O12 film

Authors: Pintilie, L; Pintilie, I; Alexe, M

Published: 1999, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 19, 1476, DOI: 10.1016/S0955-2219(98)00455-5

Ferroelectric Bi4Ti3O12 (BiT) thin films of different thicknesses were deposited on p-type Si substrates using the Chemical Solution Deposition (CSD) method. The films were crystallized by the conventional thermal annealing for 30 min at temperatures in the 500-700 degrees C range. It was found that the shape of the photoconductive signal spectral distribution is dependent on the film thickness. For thin films (150 nm) four peaks were observed (400, 500, 860 and 1075 nm) and the photoconductive signal occurs only if the Si substrate is negatively biased. For thicker films (500 nm) only two peaks were observed (370 and 1075 nm) and the photoconductive signal occurs no matter the polarity of the applied voltage. (C) 1999 Elsevier Science Limited. All rights reserved.

852. Superconductor-ferroelectric heterostructures

Authors: Constantin, C; Ramer, R; Matei, I; Trupina, L; Stegarescu, M

Published: 1999, FERROELECTRICS, 225, 1092, DOI:

Superconductor-ferroelectric heterostructures were prepared by deposition of ferroelectric doped-PZT type material on the top of the superconductor YBCO thin films. Both, ferroelectric and superconductor thin films were obtained by off-axis RF magnetron sputtering method with a single target. On these heterostructures, measurements were made in order to evidence the influence of contact between the two materials on the electrical and thermal parameters. X-ray diffraction patterns of superconductor thin film show a good crystallization c-axis oriented perpendicular to the substrate plane, and a perovskite structure without traces of pyrochlore at 550 degrees C the ferroelectric thin film deposited by RF magnetron sputtering (off axis method). Important variations of the critical temperature of superconductor films have been obtained, due to the increased dielectric permittivity (epsilon).

853. Photoconductivity of SrBi2Ta2O9 thin films

Authors: Pintilie, L; Alexe, M

Published: 1999, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 19, 1488, DOI: 10.1016/S0955-2219(98)00460-9

Photoconductive properties of SrBi2Ta2O9 thin films in the 250-400 nm wavelength range were investigated. The films were deposited on Pt/SiO2/Si substrates using the Chemical Solution Deposition and were crystallized by conventional thermal annealing at 850 degrees C. One sensitivity maximum was observed in the spectral distribution of the photoconductive signal and was attributed to band-to-band generation in the film. The wavelength corresponding to this maximum was found to be dependent on the applied voltage, on the delay time, defined as the time between the application of light on the film and the reading of the generated photocurrent, and on the wavelengths sweeping direction tug or down). The gap value was estimated to be around 3.94-4 eV. (C) 1999 Elsevier Science Limited. All rights reserved.

854. Photoelectric effects in chemical solution deposited Bi4Ti3O12 thin films

Authors: Pintilie, L; Alexe, M; Pignolet, A; Hesse, D

Published: DEC 1998, JOURNAL DE PHYSIQUE IV, 8, 104, DOI: 10.1051/jp4:1998916

Bismuth titanate ferroelectric thin films were deposited on platinum coated silicon using chemical solution deposition. Photoconductive and photovoltaic effects were observed both in continuous and modulated light. With the increasing of the annealing temperature the maximum of the photoconductive signal spectral distribution is moving toward longer wavelengths, from 340 nm to 370 nm. The existence of the photovoltaic effect could be due to some potential barriers existing at the grain boundaries and me enlargement of its spectral distribution toward longer wavelengths could be due to the presence of some traps at the grain boundaries.

855. Theoretical background of the optical charging spectroscopy method used for investigation of trapping levels

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

Published: SEP 21 1998, APPLIED PHYSICS LETTERS, 73, 1687, DOI: 10.1063/1.122245

An analytical formula for the optical charging spectroscopy (OCS) discharging current in the case of homogeneous semiconductors is deduced. The computation shows that the OCS current is proportional with the square of the initially trapped carrier concentrations. This result leads to a higher sensitivity in case of the OCS method compared with the thermally stimulated current method. The OCS current formula obtained for one trapping level is generalized in the case of many trapping levels. From the generalized formula it can be seen that the OCS current can change the sign if both electron and hole traps exist in the sample. (C) 1998 American Institute of Physics.

856. Bi4Ti3O12 ferroelectric thin film ultraviolet detectors

Authors: Pintilie, L; Alexe, M; Pignolet, A; Hesse, D

Published: JUL 20 1998, APPLIED PHYSICS LETTERS, 73, 344, DOI: 10.1063/1.121828

Bi4Ti3O12 (BiT) ferroelectric thin films were used as photoconductive or photovoltaic ultraviolet detectors. The maximum of the spectral distribution lies around 370 or 390 nm, depending on whether the incident light is continuous or modulated. The maximum current responsivity obtained for the films annealed at 700 degrees C is about 0.01 A/W. The specific detectivity is 5.5 x 10(8) cm W-1 Hz(1/2) at a modulation frequency of 20 Hz. The frequency characteristics of the photovoltaic signal measured in modulated light suggests a 1/f frequency dependence of this signal. (C) 1998 American Institute of Physics.

857. Investigation of deep impurity levels in high resistivity silicon using optical charging spectroscopy

Authors: Botila, T; Brancus, D; Pintilie, I; Pintilie, L; Petre, D

Published: 1998, DEFECT RECOGNITION AND IMAGE PROCESSING IN SEMICONDUCTORS 1997, 160, 296, DOI:

The Optical Charging Spectroscopy (OCS) was applied for the first time to investigate the trapping levels in high resistivity silicon irradiated with neutrons. An analytical formula for the OCS discharging current has been obtained. The theoretical and experimental results proved that the OCS is more sensitive than the usual Thermally Stimulated Currents method.

858. Electrical and optical characterization of PbTiO3/Si heterostructures for applications in optoelectronics

Authors: Dragoi, V; Pintilie, L; Pintilie, I; Petre, D; Boerasu, I; Alexe, M

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 851, DOI: 10.1117/12.312674

The ferroelectric/semiconductor heterostructures were fabricated by sol-gel deposition of lead titanate (PT) thin films on a single-crystalline p-type Si wafers. The ETT films were crystallyzed by a conventional thermal annealing for 30 min at temperatures ranging from 575 degrees C to 675 degrees C. Current-voltage and capacitance-voltage characteristics show a hysteresis which can be due to the spontaneous polarization of PbTiO3. The current-voltage characteristics exhibit a diode behaviour while the capacitance-voltage exhibits a large memory window, up to 3.5 V, for the films annealed at 600-650 degrees C. At the illumination with modulated light, a.c. photovoltage was detected on a broad range of wavelengths (0.35+4 mu m) for all samples. The spectral distribution of the photoelectric signal in the UV-Vis-IR domain shows two local maxima. A model is proposed to explain the observed experimental results.

859. A model of the metallic surface-emitting second harmonic generator

Authors: Popa, A; Lazarescu, MF; Dabu, R; Stratan, A

Published: SEP 1997, IEEE JOURNAL OF QUANTUM ELECTRONICS, 33, 1480, DOI: 10.1109/3.622625

We present an accurate calculation of the intensity of the second harmonic radiation generated by the reflection of the incident radiation from a metal surface, This radiation is due to two currents, The first current results from the rapid variation of the normal component of the oscillating electric field in the vicinity of the surface and depends on both conduction and bound electrons, The second one results from the action of the Lorentz force on conduction electrons, We show that if the adiabatic and the Thomas-Fermi assumptions are considered, then an accurate calculation of these currents is possible and leads to a simple relation of the intensity of the second harmonic radiation.

860. Indirect enhancement of PbS photoconductivity by ferroelectric field effect in a PbS/PbTiO3/Si heterostructure

Authors: Pintilie, I; Pintilie, L; Dragoi, V; Petre, D; Botila, T

Published: AUG 25 1997, APPLIED PHYSICS LETTERS, 71, 1106, DOI: 10.1063/1.119740

A lead sulphide/lead titanate/silicon (PbS/PbTiO3/Si) heterostructure was manufactured by successive deposition of PbTiO3 and PbS thin film on a single crystalline, p-type Si substrate. Chemical methods were used for deposition. A three electrode configuration was used to control the photoconductivity of PbS thin film by field effect, through the ferroelectric PbTiO3 thin film. The spectral distribution of the photoconductive signal shows two maxima, situated at 1.1 and 2.45 mu m. It was found that the photoconductive signal at 1 mu m varies of about eight times when the voltage applied on the Si substrate is varied between -1 and +1 V. At 2 mu m the photoconductive signal is almost independent of the applied voltage on the Si substrate. The observed results are explained considering a ferroelectric field effect by which the photogenerated carriers in Si influence the photoconductive signal in the PbS thin film. (C) 1997 American Institute of Physics.