Er related 1.53 μm emission from Er-Si-codoped ZnO multilayer film prepared by rf-sputtering

The near-infrared emission from Er and Si codoped ZnO film, synthesized by cosputtering from separated Er, Si, and ZnO targets, has been investigated. By building the multilayer film structure, controlling the Er concentration, and optimizing the annealing condition, the intensity of Er³⁺ related 1.53 μm photoluminescence (PL), which originates from the transition of Er³⁺: ⁴I_13/2 → ⁴I_15/2, can be modulated. It is shown that the maximum intensities of Er³⁺ related 1.53 μm PL are obtained when the Si:ZnO/Er:Si:ZnO/Si:ZnO sandwiched multilayer film and the alternate Er:ZnO/Si:ZnO multilayer film were annealed at 1000 °C and 950 °C, respectively. The Er³⁺ related 1.54 μm PL intensity of the multilayer film is higher than that of the Er:ZnO monolayer film. This can be attributed to the presence of the silicon nanocrystals that could act as sensitizers of Er³⁺ ions in the multilayer film. The PL of the sandwiched multilayer film and the alternate multilayer film were measured under different temperatures (15-300 K). The sandwiched multilayer film exhibits a nonmonotonic temperature dependence as well as the alternate multilayer film, which differs from that of Er-doped ZnO as previously reported.     

Enhanced photoluminescence response of Er-Si nanoparticle codoped Al2O3 films by controlled synthesis in the nanoscale and thermal processing

Nanostructured Er³⁺-Si nanoparticles (NPs) codoped Al₂O₃ films were synthesized by a one step laser based deposition process which allows to form the Si NPs in situ at room temperature, and to control their size and separation with the Er ions in the nanoscale. Two different thermal annealing treatments are studied in order to optimize the photoluminescence (PL) emission: rapid thermal annealing (RTA) at 900 °C during 2 min, and conventional furnace step annealing at different temperatures up to 750 °C for 1 h. After RTA process the films show an important enhancement on the photoluminescence lifetime values which is related to a reduction of the non-radiative decay channels. Nevertheless, the Si NPs to Er ions energy transfer is strongly reduced. In contrast after conventional furnace annealing up to 700 °C, although there is only a moderate increase of the photoluminescence lifetime values, the excitation of Er ions through Si NPs is still active and as a consequence a large enhancement of the photoluminescence intensity with respect to the Er-only doped film is achieved. These different behaviours are most likely related to structural and chemical changes in the Er environment upon the different annealing processes.     

Sol-gel preparation of near-infrared broadband emitting Er-doped SiO2-Ta2O5 nanocomposite films

This article reports a study on the preparation, densification process, and structural and optical properties of SiO₂-Ta₂O₅ nanocomposite films obtained by the sol-gel process. The films were doped with Er³⁺, and the Si:Ta molar ratio was 90:10. Values of refractive index, thickness and vibrational modes in terms of the number of layers and thermal annealing time are described for the films. The densification process is accompanied by OH group elimination, increase in the refractive index, and changes in film thickness. Full densification of the film is acquired after 90 min of annealing at 900 °C. The onset of crystallization and devitrification, with the growth of Ta₂O₅ nanocrystals occurs with film densification, evidenced by high-resolution transmission electron microscopy. The Er³⁺-doped nanocomposite annealed at 900 °C consists of Ta₂O₅ nanoparticles, with sizes around 2 nm, dispersed in the SiO₂ amorphous phase. The main emission peak of the film is detected at around 1532 nm, which can be assigned to the ⁴I_13/2 → ⁴I_15/2 transition of the Er³⁺ ions present in the nanocomposites. This band has a full width at half medium of 64 nm, and the lifetime measured for the ⁴I_13/2 levels is 5.4 ms, which is broader compared to those of other silicate systems. In conclusion, the films obtained in this work are excellent candidates for use as active planar waveguide.     

Preparation and thermoelectric properties of nc-Si:(Al2O3 + SiO2) composite film

A composite film of nanocrystalline Si (nc-Si) embedded in (Al₂O₃ + SiO₂) has been prepared on a quartz substrate by thermally evaporating a 400 nm thick Al film on a quartz substrate and annealing in air at 580 °C for 1 h. During annealing, the Al reacts with the SiO₂ of the quartz substrate and produces nc-Si, which is embedded in the (Al₂O₃ + SiO₂) film. The average size of nc-Si is ~ 22 nm and the thickness of the nc-Si:(Al₂O₃ + SiO₂) composite film is ~ 810 nm. It is found that the prepared film is thermoelectric with a Seebeck coefficient of − 624 μV/K at 293 K and − 225 μV/K at 413 K.     

Preparation and photoluminescence of Er-doped Al2O3 films by sol-gel method

The 0-1.5 mol% Er³⁺-doped Al₂O₃ films have been prepared on the thermally oxidized SiO₂/Si(100) substrate in the dip-coating process by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with the addition of erbium nitrate [Er(NO₃)₃·5H₂O]. The continuous Er³⁺-doped Al₂O₃ films with the thickness of about 1.2 μm were obtained for nine coating cycles at a sintering temperature of 900 °C. The aggregate size for the Er³⁺-doped Al₂O₃ films increased with increasing the Er³⁺ doping concentration from 0 to 1.5 mol%. The root-mean-square roughness of the films was independent on the Er³⁺ doping, which was about 1.8 nm for the 0-1.5 mol% Er³⁺-doped Al₂O₃ films. The γ-Al₂O₃ phase with a (110) preferred orientation was produced for the Al₂O₃ film. The photoluminescence (PL) spectra of 0.1-1.5 mol% Er³⁺-doped Al₂O₃ films were observed at the measurement temperature of 10 K. There was no significant change for the PL peak intensity with the increase of Er³⁺ doping concentration from 0.1 to 1.5 mol%, and similar full width at half maximum of about 40 nm was detected for the 0.1-1.5 mol% Er³⁺-doped Al₂O₃ thin films. The Er³⁺-doped Al₂O₃ films possess the available PL properties for use in planar optical waveguides.     

Composition, surface morphology and electrical characteristics of Al2O3-TiO2 nanolaminates and AlTiO films on silicon

We propose and demonstrate Metal-Oxide-Semiconductor structures comprising Al₂O₃-TiO₂ nanolaminate and AlTiO films. Composition, structural and electrical characteristics were studied in detail and compared to TiO₂ thin film-based structures. All dielectric films were evaporated using an electron beam gun (EBG) system on unheated p-Si substrate without adding O₂. MOS structures were investigated in detail before and after annealing at up to 950 °C in O₂ and N₂ + O₂ environments. The nanolaminate films remain in an amorphous state after annealing at 950 °C. The smallest quantum mechanical corrected equivalent oxide thickness measured was ∼1.37 nm. A large reduction of the leakage current density to 1.8 × 10^− 8 A/cm² at an electric field of 2 MV/cm was achieved by the annealing process.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Investigation of electronic structure of Si nanocrystals and their interface with host matrix in P-doped SiO2:Si and Al2O3:Si nanocomposites

The system of the nanoinclusions of Si in the SiO₂ and Al₂O₃ matrix (SiO₂:Si, Al₂O₃:Si) attracts great attention due to its ability of the luminescence in visible and near-IR range of spectrum. The influence of the P ion alloying on the electronic structure of nanocomposites was investigated. The P ion doping and post-annealed at T = 1000 °C (2 h) results in the enhancement of the photoluminescence (PL) peak connected with the Si nanocrystals. The electronic structure was investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy losses spectroscopy (HREELS) methods. Ion surface modification and annealing forms the special nanostructure with Si nanocrystals in SiO₂ and Al₂O₃ matrix having high density of interfaces with special atomic structure and various degree of oxidation of Si atoms on the boundaries. HREELS investigations show that the P ion doping increases the probability of interband transitions in SiO₂:Si and Al₂O₃:Si composites.     

Temperature effects on the growth and electrical properties of Er2O3 films on Ge substrates

Er₂O₃ films were grown on Ge (001) substrates at different temperatures by molecular beam epitaxy using metallic Er and molecular oxygen sources with otherwise identical conditions. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the microstructures and compositions of the films. The film deposited at room temperature is found to be composed of an Er₂O₃ layer and an ErGe_xO_y interface layer with a thickness of 5.5 nm; the film grown at 300 °C has a mixed structure of Er₂O₃ and ErGe_xO_y and the thickness was found to be reduced to 2.2 nm; the film grown at 450 °C becomes much rougher with voids formed underneath the film, having a mixed structure of three compounds of Er₂O₃, GeO and ErGe_xO_y. The growth mechanisms of the films at different temperatures are suggested. Current images obtained by tunneling atomic force microscopy show that the film grown at 450 °C has much more leaky spots than those grown at RT and 300 °C, which may arise from the formation of volatile GeO in the film.     

The preparation of Zn-ferrite epitaxial thin film from epitaxial Fe3O4:ZnO multilayers by ion beam sputtering deposition

A new method to grow a well-ordered epitaxial ZnFe₂O₄ thin film on Al₂O₃(0001) substrate is described in this work. The samples were made by annealing the ZnO/Fe₃O₄ multilayer which was grown with low energy ion beam sputtering deposition. Both the Fe₃O₄ and ZnO layers were found grown epitaxially at low temperature and an epitaxial ZnFe₂O₄ thin film was formed after annealing at 1000 °C. X-ray diffraction shows the ZnFe₂O₄ film is grown with an orientation of ZnFe₂O₄(111)//Al₂O₃(0001) and ZnFe₂O₄(1-10)//Al₂O₃(11-20). X-ray absorption spectroscopy studies show that Zn²⁺ atoms replace the tetrahedral Fe²⁺ atoms in Fe₃O₄ during the annealing. The magnetic properties measured by vibrating sample magnetometer show that the saturation magnetization of ZnFe₂O₄ grown from ZnO/Fe₃O₄ multilayer reaches the bulk value after the annealing process.     

Effect of heat treatment on the microstructure and property of cold-sprayed nanostructured FeAl/Al2O3 intermetallic composite coating

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using compound feedstock powders due to their intrinsic low temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post heat treatment. In this study, a nanostructured Fe(Al)/Al₂O₃ composite alloy coating was prepared by cold spraying of ball-milled powder. The cold-sprayed Fe(Al)/Al₂O₃ composite alloy coating was evolved in-situ to FeAl/Al₂O₃ intermetallic composite coating through a post heat treatment. The effect of heat treatment on the phase formation, microstructure and microhardness of cold-sprayed Fe(Al)/Al₂O₃ composite coating was investigated. The results showed that annealing at a temperature of 600 °C results in the complete transformation of the Fe(Al) solid solution to a FeAl intermetallic compound. Annealing temperature significantly influenced the microstructure and microhardness of the cold-sprayed FeAl/Al₂O₃ coating. On raising the temperature to over 950 °C, diffusion occurred not only in the coating but also at the interface between the coating and substrate. The microhardness of the FeAl/Al₂O₃ coating was maintained at about 600HV_0.1 at an annealing temperature below 500 °C, and gradually decreased to 400HV_0.1 at 1100 °C.     

Structural and optical properties of Er-doped Y2Ti2O7 thin films by sol-gel method

Er³⁺-doped Y₂Ti₂O₇ and Er₂Ti₂O₇ thin films were fabricated by sol-gel spin-coating method. A well-defined pyrochlore phase Er_xY_2-xTi₂O₇ was observed while the annealing temperature exceeded 800 °C. The average transmittance of the Er_xY_2-xTi₂O₇ thin films annealed at 400 to 900 °C reduces from ∼ 87 to ∼ 77%. The refractive indices and optical band gaps of Er_xY_2-xTi₂O₇ (x = 0-2) annealed at 800 °C/1 h vary from 2.20 to 2.09 and 4.11 to 4.07 eV, respectively. The ∼ 1.53 μm photoluminescence spectrum of Er³⁺ (5 mol%)-doped Y₂Ti₂O₇ thin films annealed at 700 °C/1 h exhibits the maximum intensity and full-width at half maximum (∼ 60 nm).     

Luminescent properties of Gd2Ti2O7: Eu phosphor films prepared by sol-gel process

Gd₂Ti₂O₇: Eu³⁺ thin film phosphors were fabricated by a sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800 °C and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. The doped Eu³⁺ showed orange-red emission in crystalline Gd₂Ti₂O₇ phosphor films due to an energy transfer from Gd₂Ti₂O₇ host to them. Both the lifetimes and PL intensity of the Eu³⁺ increased with increasing the annealing temperature from 800 to 1000 °C, and the optimum concentrations for Eu³⁺ were determined to be 9 at.%. of Gd³⁺ in Gd₂Ti₂O₇ film host.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

Post deposition annealing temperature effect on silicon quantum dots embedded in silicon nitride dielectric multilayer prepared by hot-wire chemical vapor deposition

The preparations of the 20-period of a Si quantum dot (QD)/SiN_x multilayer in a hot-wire chemical vapor deposition (HWCVD) chamber is presented in this paper. The changes in the properties of Si-QDs after the post deposition annealing treatment are studied in detail. Alternate a-Si:H and SiN_x layers are grown in a single SiN_x deposition chamber by cracking SiH₄, and SiH₄ + NH₃, respectively at 250 °C. The as-deposited samples are annealed in the temperature range of 800 °C to 950 °C to grow Si-QDs. All the samples are characterized by confocal micro Raman, transmission electron microscope (TEM), and photoluminescence (PL) to study the changes in the film structures after the annealing treatment. The micro Raman analysis of the samples shows the frequency line shifting from 482 cm^− 1 to 500 cm^− 1 indicating the Si transition from an amorphous to a crystalline phase. The TEM micrograph inspection indicates the formation of Si-QDs of size 3 to 5 nm and a density of 5 × 10¹²/cm². The high resolution TEM micrographs show an agglomeration of Si-QDs with an increase in the annealing temperature. The PL spectra show a peak shifting from 459 nm to 532 nm with increasing the annealing temperature of the film.     

Characterization of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Microstructural characterization of pulsed laser deposited Al₂O₃/ZrO₂ multilayers on Si (1 0 0) substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar and at room temperature (298 K) has been carried out. A nanolaminate structure consisting of alternate layers of ZrO₂ and Al₂O₃ with 40 bi-layers was fabricated at different zirconia layer thicknesses (20, 15 and 10 nm). The objective of the work is to study the effect of ZrO₂ layer thickness on the stabilization of tetragonal ZrO₂ phase for a constant Al₂O₃ layer thickness of 5 nm. The Al₂O₃/ZrO₂ multilayer films were characterized using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1473 K. The studies showed that the thickness of the zirconia layer has a profound influence on the crystallization temperature for the formation of tetragonal zirconia phase. The tetragonal phase content increased with the decrease of ZrO₂ layer thickness. The cross-sectional transmission electron microscope (XTEM) investigations were carried out on a multilayer thin films deposited at room temperature. The XTEM studies showed the formation of uniform thickness layers with higher fraction of monoclinic and small fraction of tetragonal phases of zirconia and amorphous alumina.     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba_0.5Sr_0.5TiO₃(BST)/Bi_1.5Zn_1.0Nb_1.5O₇(BZN) multilayer thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. The structures and morphologies of BST/BZN multilayer thin films were analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscope. The XRD results showed that the perovskite BST and the cubic pyrochlore BZN phases can be observed in the multilayer thin films annealed at 700 °C and 750 °C. The surface of the multilayer thin films annealed at 750 °C was smooth and crack-free. The BST/BZN multilayer thin films annealed at 750 °C exhibited a medium dielectric constant of around 147, a low loss tangent of 0.0034, and a relative tunability of 12% measured with dc bias field of 580 kV/cm at 10 kHz.     

Overview of optical properties of Al2O3 films prepared by various techniques

We study optical properties of Al₂O₃ films prepared by various techniques using spectroscopic ellipsometry. The film preparation techniques include conventional pulsed magnetron sputtering in various gas mixtures, high power impulse magnetron sputtering, annealing of as-deposited Al₂O₃ in an inert atmosphere and annealing of as-deposited Al in air. We focus on the effect of the preparation technique, deposition parameters and annealing temperature on the refractive index, n, and extinction coefficient, k, of stoichiometric Al₂O₃. At a wavelength of 550 nm we find n of 1.50-1.67 for amorphous deposited Al₂O₃, 1.65-1.67 for amorphous Al₂O₃ obtained by Al annealing, 1.46-1.69 for γ-Al₂O₃ and decreasing n for Al₂O₃ annealing temperature increasing up to 890 °C. The results facilitate correct interpretation of optical characterization of Al₂O₃, as well as selection of a preparation technique corresponding to a required Al₂O₃ structure and properties.     

Single-source chemical vapor deposition of clean oriented Al2O3 thin films

Clean oriented Al₂O₃ thin film with a dominant Al₂O₃ <1 1 3> plane was deposited on Si <1 0 0> substrate at 550 °C, by single-source chemical vapor deposition (CVD) using aluminium(III) diisopropylcarbamate, Al₂(O₂CNⁱPr₂)₆. This process represents a substantial reduction in typical CVD film growth temperatures which are typically > 1000 °C. Through the studies of thermal stability of this precursor, we propose a specific β-elimination decomposition pathway to account for the low temperature of the precursor decomposition at the substrate, and for the lack of carbon impurity byproducts in the resulting alumina films that are characterized using X-ray photoelectron spectroscopy and depth profiling.