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Development of bulk acoustic wave filters with ultra-wide pass bands and operating at high frequencies for 5th and 6th generation telecommunication applications and micro-scale actuators, energy harvesters and sensors requires lead-free piezoelectric thin films with high electromechanical coupling and compatible with Si technology. In this paper, the epitaxial growth of 36°Y-X and 30°X-Y LiNbO3 films by direct liquid injection chemical vapour deposition on Si substrates by using epitaxial SrTiO3 layers, grown by molecular beam epitaxy, has been demonstrated. The stability of the interfaces and chemical interactions between SrTiO3, LiNbO3 and Si were studied experimentally and by thermodynamical calculations. The experimental conditions for pure 36°Y-X orientation growth have been optimized. The piezoelectricity of epitaxial 36°Y-X LiNbO3/SrTiO3/Si films was confirmed by means of piezoelectric force microscopy measurements and the ferroelectric domain inversion was attained at 85 kV.cm−1 as expected for the nearly stoichiometric LiNbO3. According to the theoretical calculations, 36°Y-X LiNbO3 films on Si could offer an electromechanical coupling of 24.4% for thickness extension excitation of bulk acoustic waves and a comparable figure of merit of actuators and vibrational energy harvesters to that of standard PbZr1− x Ti x O3 films. [ABSTRACT FROM AUTHOR]

Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol–gel/spin-coating approach of polycrystalline LiNbO3 films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol–gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO3 films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films. [ABSTRACT FROM AUTHOR]

The photoluminescence of undoped ZnO single crystals up to 1350 °C and the optical absorption of stress-relaxed, epitaxial ZnO thin films up to 1100 °C are reported. The photoluminescence intensity and power dependence with illumination flux are related to the crystal growth methods and stabilize after high temperature annealing. The observation of excitonic recombination at very high temperatures requires high illumination flux. It is found that the zero phonon line model reproduces the shift and the band gap narrowing as well as the free excitonic transition up to the cross-over with a defect level at 2.83 eV that occurs at 800 °C. A phenomenological model of the excitonic recombination band shape, taking account exciton-phonon losses and defect levels provides an excellent fit up to 2.2-2.4 eV (1100 °C). At these cross-over temperatures, an energy transfer is observed between the free exciton transition and defect transitions. However, at temperature above 1100 °C, the decrease of the band gap and the increase of thermal radiation, as well as the restrictions of our experimental set-up and particularly the illumination flux of the exciting laser, limit the analysis of the photoluminescence spectra measurements. [ABSTRACT FROM AUTHOR]

Over the past five decades, LiNbO3 and LiTaO3 single crystals and thin films have been studied intensively for their exceptional acoustic, electro-optical, and pyroelectric and ferroelectric properties. Today, LiNbO3 single crystals in electro-optics are equivalent to silicon in electronics, and about 70% of radio-frequency (RF) filters, based on surface acoustic waves, are fabricated on these single crystals. These materials in the form of thin films are needed urgently for the development of the next-generation of high-frequency and/or wide-band RF filters or tuneable frequency filters adapted to the fifth generation of infrastructures/networks/communications. The integration of LiNbO3 films in guided nanophotonic devices will allow higher operational frequencies, wider bandwidth, and miniaturized optical devices in line with improved electronic conversion. Here, the challenges and the achievements in the epitaxial growth of LiTaO3 and LiNbO3 thin films and their integration with silicon technology and to acoustic and guided nanophotonic devices are discussed in detail. The systematic representation and classification of all epitaxial relationships reported in the literature have been carried out in order to help the prediction of the epitaxial orientations in the new heterostructures. Future prospects of potential applications and the expected performances of thin film devices are overviewed, as well. [ABSTRACT FROM AUTHOR]

Photoluminescence of (0001) epitaxial ZnO films with thicknesses of 10, 30 and 100 nm on C-sapphire substrates have been studied at room temperature and after exposure to Ar, Ar-O2, Ar-N2 and Ar-H by remote microwave and radiofrequency plasmas. The photoluminescence are not modified by remote plasma treatments where only neutral species were involved. On the contrary, the photoluminescence signal is enhanced or quenched after radiofrequency plasma treatments when energetic ion species are involved in the surface treatment processes. Little changes of electric properties are observed, however, the optical transmission indicates that the absorption edge and probably also the index of refraction are affected. Photoluminescence peak shifts, widths and intensities changes show very strong similarities with polarized emission of ZnO single crystal where it exists a strong dichroism. The photoluminescence emission properties may then result from this optical modification. However, the plasma treatments on the different samples show very low stability in time, except, for the treatment in argon plasma alone. In this later case, in-situ monitoring of photoluminescence as a function of temperature revealed a partial recovery of the photoluminescence properties after a heat treatment at 400 °C for few minutes. These results indicate that photoluminescence of (0001) ZnO thin film, related to σ-emission polarized emission from c-axis polar surfaces, is highly affected by surface and implanted charged species. [ABSTRACT FROM AUTHOR]

A Systematic study of domain Structure and residual stress evolution with film thickness and of phase transition in c/a epitaxial PbTiO3/LaAlO3 films using X- ray diffraction and Ranian spectroscopy is reported. Both techniques revealed that the films are under tensile residual stress in the film plane and that a-domains are more stressed than c-domains. The two components of the large A1(TO) Raman modes are associated with a- and c-domains and their intensity ratio correlates to the volume fraction of a-domains. The evolution of the Raman signature with temperature revealed that the spectrum of a-domains disappears around 480°C, whereas c-domains present an anomaly in their spectrum at 500° C but maintain a well- defined Raman signature up to 600°C. [ABSTRACT FROM AUTHOR]

This work reports the deposition and characterization of piezoelectric ZnO thin films on semi-insulating GaAs substrates for the fabrication of bulk acoustic waves sensors. ZnO films are deposited at 350 °C and low deposition rate using reactive radio frequency magnetron sputtering. The use of a Pt bottom electrode, between ZnO and GaAs, with and without Ti buffer layer, as well as the effect of the substrate crystallographic orientation are investigated. The characterization of the deposited films is performed to determine the optimal parameters for obtaining high-quality films and ZnO residual conductivity. ZnO films are textured along the c-axis for all GaAs cuts. The highest structural quality is obtained on (100) GaAs substrates. Moreover, the presence of the Ti buffer layer improves the texture quality, surface roughness and residual stresses. The lowest residual conductivity is determined for the ZnO/Pt/Ti/GaAs structure. However, a slight diffusion of Ga and Ti into Pt is observed, which may be of concern if Pt is used as a bottom electrode. Therefore, for thickness excitation functioning, further optimization of the Pt/GaAs interface has to be considered. • High quality ZnO films are grown on GaAs at low temperature. • ZnO and Pt/ZnO on GaAs are investigated for the integration in GaAs technologies. • Pt/ZnO is investigated with Ti additional adhesion layers. • Pt buried electrode on GaAs is characterized by interdiffusion through Pt. [ABSTRACT FROM AUTHOR]

Reducing the irradiation damage in materials processed by crystal ion slicing (CIS) is pivotal for recovering the properties linked to the materials' structure, which enables the performance of related devices. The study of the X-ray diffuse scattering allows to understand the mechanism of thermal recrystallization in CIS-processed materials, which facilitates the optimal design of the crystallinity recovery process. [Display omitted] • Optimal recovery of crystal ion slicing-processed LiNbO 3 crystallinity achieved through 2 h, 200 °C annealing post crystal-ion-slicing. • The recovery of the crystallinity involves the rearrangement of CIS-induces point defects and their clusters into dislocation loops and cascade. • Post-CIS annealing at temperature 200 °C above the split temperature induces non-correlated dislocations and increases the in-plane stress. • The findings in this work support the optimization of the design of LiNbO 3 thin-film bulk acoustic wave filters. LiNbO 3 (LNO) is a material suitable for high-frequency and wideband RF filters as well as photonic applications due to its outstanding piezoelectric and optical properties. Applications such as thin-film bulk acoustic wave resonators or highly confined electro-optic modulators require thin films, which are still challenging to be obtained with the necessary crystalline quality by deposition methods. Alternatively to deposition, crystal ion-slicing (CIS) or Smart CutTM enables obtaining thin films hundreds of nanometers thick from the bulk single-crystal utilizing high-energy and dose implantation of light atoms. The price to pay is the partial degradation of the initial crystalline perfection, which translates to a degradation of the piezoelectric performance of the material if the CIS-induced damage is not eliminated. This work aims to understand the physics of the recrystallization process of the CIS-damaged LNO crystal upon thermal annealing. The study of the coherent and diffuse scattering by high-resolution X-ray diffraction, complemented by micro-Raman backscattering spectroscopy and Transmission Electron Microscopy (TEM), allowed to study the recovery of the crystallinity from the CIS-induced lattice strain and stress and the progressive reduction of the defects clusters dimension. [ABSTRACT FROM AUTHOR]