The integration of ferroelectric materials as thin films has attracted considerable attention these last years thanks to their outstanding performances that allow considering new features for the realization of photovoltaic devices. Our study focuses on investigating structural, dielectric and ferroelectric properties of undoped and Mn doped PZN-4.5PT nanoparticles thin films on Silicon substrate. We fabricate very stable PZN-4.5PT nanoparticles thin films deposited on nanostructured silicon substrate with giant relative dielectric permittivity of 2.76 × 10 4 and 17.7 × 10 4 for respectively the undoped and Mn doped thin films. These values are very large compared to those found in single crystals and might be explained by the influence of the gel in which nanoparticles were dispersed. The SEM images show the crystallization of new hexagonal phases on the film surface probably coming from interaction between Si and the gel. The hysteresis loops permitted to determine the spontaneous polarization (P s), remnant polarization (P r) and coercive field E c which are equal to 11.73 μC/cm 2, 10.20 μC/cm 2 and 20 V/cm, respectively for the undoped nanoparticles thin film and 22.22 μC/cm 2, 19.32 μC/cm 2 and 20 V/cm respectively for the Mn doped one. These values are high and correspond to the best ones found in literature compared to typical ferroelectric thin films.
For semiconductor photovoltaic materials, photons with energy higher than the band gap are absorbed to produce electron-hole pairs which are separated by the internalfield in the p-n junction and collected by the electrodes. Consequently, the photo-induced voltage is limited by the energy barrier height at the interface region and usually smaller than the semiconductor band-gap [
Recently, the discovery of perovskite ferroelectric nanomaterials opened up a great possibility of application for ferroelectric devices. There have been various nanostructures such as nanoparticles, nanorods, and nano-patterned structures using PZT, BaTiO3, and SrTiO3 [
In this paper, to integrate them into silicon nanostructures, we realized PZN-4.5PT nanoparticles deposition, already synthesized by the so-called solution flux method [
Undoped and 1% Mn doped PZN-4.5PT grounded powders were dispersed in gel fabricated in the laboratory LCPM in Assane Seck University of Ziguinchor. To obtain a homogeneous film, spinning process was carried out at room temperature using a spin coater Midas 1200 D at 3500 rpm with an initial acceleration time of 5 seconds and an operating time of 10 min. After 10 min bake in oven at 100˚C, thermal annealing in a K114 type muffle furnace was performed. The heating rate of the furnace is chosen between 10 and 20˚C/min. A 30 - 60 min plateau was carried out at 900˚C for the gel diffusion through the p-type silicon (<100> oriented Boron doped monocrystalline silicon with resistivity 5 - 10 Ω.cm and thickness of 600 - 650 μm) nanowires substrate. Cooling at ambient temperature was done naturally. Different samples were fabricated using the two nanopowders and were characterized. Surface morphology of thin films samples were observed using an electron beam lithography system Pioneer Raith model in C(PN)2 (Paris 13 University).
For dielectric properties characterization, the sample with the deposit thin film was metallized on the both sides with silver paste using the screen-printing method. In order to have good adhesion between the silver and the thin layer, the metallized sample was annealed at 450˚C for 30 min in a thermo scientific model FB1310M-33 oven. For dielectric losses measurements and to calculate the relative dielectric constant (εr), the capacity measurements as function of the temperature and the frequency were performed using a LCR meter model LCR-819 from GWINSTEK. The relative dielectric constant was determined using the following formula
ε r = C e S ε 0 (1)
where C is the measured capacity, e the thickness, S the metallized surface and ε0 the vacuum permittivity (8.85.10−12 F/m). A modified Sawyer-Tower circuit at room temperature was used to measure the polarization versus the DC field. From polarization-Efield curves, Ec, Pr and Ps were determined.
to give a hexagonal nano-crystals; on the other hand it is possible that there is a reaction between Pb and the gel giving these nano-crystals), which could be explained by the formation of a new phase and due to the presence of new atoms from the gel containing nanoparticles such as Pb and P that may form new hexagonal complexes with Si thanks to annealing. In
Thin films | εr (1 kHz) ambient T | tanδe (%) ambient T | TRT (˚C) | Tc (˚C) | εrmax (at Tc) | Ps (µC/cm2) | Pr (µC/cm2) | Ec (V/cm) |
---|---|---|---|---|---|---|---|---|
NW-PZN-4.5PT | 2.76 × 104 ± 100 | 6.45 ± 1 | 130 ± 1 | 310 ± 1 | 2.60 × 107 ± 100 | 11.73 ± 0.1 | 10.20 ± 0.1 | 20 ± 1 |
PZN-4.5PT + 1% Mn | 17.7 × 104 ± 100 | 5.00 ± 1 | 130 ± 1 | 305 ± 1 | 3.00 × 107 ± 100 | 22.22 ± 0.1 | 19.32 ± 0.1 | 20 ± 1 |
could be explained by the new phase from combination of Si-perovskite-gel overgrowth on the silicon surface. The dielectric losses are low compared to other high K materials; their values are equal to 6.45% and 5% respectively for the undoped and Mn doped PZN-4.5PT thin films. These values show that the mechanical factor would be very interesting and high. The results from dielectric measurements show the potential application of such materials in micro and nanoelectronic devices as a colossal relative dielectric permittivity material.
These results show that this new material could support very large electric field change (40 - 60 V/cm) compared to the other thin films dielectric. However,
over a certain value its performances would decrease. It exists a critical electric field value (around 60 V/cm) corresponding to the maximum dielectric permittivity for these materials polarization. The Mn doping did not greatly affect the thin films properties. However, it is clear that it stabilizes the electric field dependence (values are more stable compared to undoped). Indeed, one can see in
This kind of behavior usually comes from the space charges at low frequencies. Along with the improvement in the dielectric constant, an increase in the dielectric loss (
undoped and Mn doped samples. The presence of bias since it is equal to 0 V increases highly the permittivity values and behavior both for the two films. As explained above, this could be due to charge injection and accumulation. These large relative dielectric values and low dielectric losses make these materials interesting candidates for ferrophotovoltaic and energy storage.
the PZN-PT thin films at room temperature. The tunability ((εmax − εmin)/εmax) of the doped PZN-PT thin films is around 86%. This film showed very high tunability compared to those found in other ferroelectric materials such as the BNT-BT-ST thin films (29% and 35% [
and 22.22 µC/cm2, 19.32 µC/cm2 and 20 V/cm respectively for the Mn doped thin film. These values are large (high) and correspond to the best ones found in literature compared to typical ferroelectric thin films. One can see that Mn doping increases the polarization values. This is normal compared to the dielectric constant value in room temperature at 1 kHz increasing by doping (
In this study, we fabricate with success PZN-4.5PT nanoparticles thin films. Their ferroelectric behavior has been demonstrated, measured and evaluated. We found colossal dielectric constant, which could be explained by the presence of new crystals components probably coming from the reaction between Si and the gel where nanoparticles were dispersed. These results make such thin films very potential candidates for energy storage and for ferrophotovoltaic application.
The determination of the composition of these hexagonal nanocrystals on the film surface and the origin of such colossal relative permittivity would be investigated.
This work is supported by Agence Universitaire de la Francophonie (AUF).
The authors declare no conflicts of interest regarding the publication of this paper.
Ndioukane, R., Touré, M., Kobor, D., Motte, L., Solard, J. and Lebrun, L. (2019) Dielectric and Ferroelectric Properties of PZN-4.5PT Nanoparticles Thin Films on Nanostructured Silicon Substrate for Ferrophotovoltaic and Energy Storage Application. Journal of Modern Physics, 10, 613-623. https://doi.org/10.4236/jmp.2019.106043