Ultraviolet-assisted Pulsed Laser Deposition Research Articles

Er 3+,Yb 3+:YVO 4 waveguides deposited on amorphous SiO 2 by PLD and UVPLD

In this work, erbium, and erbium and ytterbium co-doped YVO 4 waveguiding thin films were deposited on amorphous SiO 2 substrates by pulsed laser deposition (PLD) and ultraviolet-assisted pulsed laser deposition (UVPLD). The influence of the deposition technique on the structure, morphology, and optical properties of the films was investigated. At lower dopant concentrations the films prepared by UVPLD show better crystallinity and optical properties. All the samples show preferred orientation of the (001) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes ∆ n (∆ n = n TE − n TM) for the TE and TM polarizations.

Highly conducting indium tin oxide films grown by ultraviolet-assisted pulsed laser deposition at low temperatures

Indium tin oxide films grown by conventional and ultraviolet-assisted pulsed laser deposition technique (PLD and UVPLD) on Si and Corning glass were analyzed by grazing and symmetric incidence X-ray diffraction. Films deposited at substrate temperatures up to 70 °C were amorphous, while films deposited at temperatures of 120 °C and higher showed good crystallinity, with a (222) texture. The diffraction peaks were split indicating that the films contained a two-layer structure. X-ray reflectivity studies showed that the film surface roughness was below 0.5 nm and their density approximately 7.20 g/cm3. Spectroscopic ellipsometry measurements indicated that the films were highly transparent, while X-ray photoelectron spectroscopy investigations showed homogeneous bulk chemical composition and a very small Sn enrichment in the surface region. The carrier mobility was rather high for films deposited at 40 and 70 °C and then decreased with the increase of the substrate temperature, because the onset of crystallization at such low temperatures produces a defective structure.

Enhanced Crystalline and Magnetic Properties of Co-Doped TiO[sub 2] Films Grown by Ultraviolet-Assisted Pulsed Laser Deposition

Using in situ ultraviolet irradiation during pulsed laser deposition (UVPLD), enhanced magnetic properties (larger remanence and coercivity) were obtained in Co-doped anatase TiO 2 films. The UVPLD grown films exhibited smaller full width at half-maximum value for the (004) peak of the Co-doped TiO 2 layer, indicating higher crystallinity. No superparamagnetic behavior was examined in the zero field cooled/field cooled measurements, suggesting an intrinsic diluted magnetic semiconductor characteristic. X-ray photoelectron spectroscopy results indicated that the cobalt in the films was in the +2 formal oxidation state and a much stronger binding coordination between oxygen and cations (Co and Ti) was inferred in the UVPLD grown films.

Ferromagnetism of anatase Ti1−XCoXO2−δ films grown by ultraviolet-assisted pulsed laser deposition

We report the effect of ultraviolet irradiation during pulsed laser deposition on the growth of cobalt-doped TiO2 films in terms of the crystalline and magnetic properties. Due to more active oxygen gas species created by photodissociation and enhanced atomic migration on the substrate surface, highly crystalline films could be obtained at a relatively low deposition temperature of 400 °C. The full width at half maximum of the (004) peak rocking curve was 0.46° for the UV-assisted film deposited at 400 °C on the LaAlO3(001) substrate. Fourfold symmetry was observed in phi scans of the Ti0.93Co0.07O2−δ film, which indicated that this film was grown in cube-on-cube epitaxial orientation with the [001] normal to the LaAlO3(001) substrate surface. The temperature dependence of the zero-field-cooled/field-cooled magnetization was examined and the hysteresis was clearly identified by the nonzero difference between them. The Curie temperature was estimated to be well over 350 K, and at room temperature the coercive field was ∼180 Oe and the remanence was ∼17% of the saturation magnetization. The in-depth distribution of the constituent elements was characterized by Auger depth profiling. No segregation was found at the surface of the film and the interdiffusion between the substrate and the film was significantly reduced at the low deposition temperature used.

Microstructural and electrochemical properties of lithium manganese oxide thin films grown by pulsed laser deposition

The pulsed laser deposition (PLD) and one of its variants, the ultraviolet assisted pulsed laser deposition (UVPLD) techniques were used to deposit LiMn 2O 4 films on various substrate materials. The effects of processing variables on microstructural and electrochemical characteristics of the grown films were evaluated. Films possessing higher crystallinity were obtained at higher deposition temperatures while for identical deposition conditions UVPLD films possessed a higher degree of crystallinity and a smaller lattice constant than those grown by PLD. An oxygen-rich, defective spinel phase was identified for films deposited using the UVPLD method. The diffusion coefficient of Li for these films, measured using cyclic voltammetry, was found to reach much higher values, of around ∼10 −8 cm 2/s, for those deposited at lower temperatures compared with only ∼10 −10 cm 2/s values found for films deposited at higher temperatures.

Ultraviolet-Assisted Pulsed Laser Deposition of Barium Strontium Titanate on Si: Characterization of the Interfacial Layer

AbstractBarium strontium titanate (BST) thin films were grown directly on Si substrates by the conventional and ultraviolet-assisted pulsed laser deposition techniques. X-ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, current-voltage, capacitance-voltage, and high-resolution transmission electron microscopy were used to investigate the composition, thickness, and electrical properties of the grown structures. It has been found that at the interface between the Si substrate and the grown dielectric layer, an interfacial layer was always formed. The chemical composition of the layer consisted of SiOx partially mixed with the grown BST, without any evidence of silicate formation.

Ultraviolet-assisted pulsed laser deposition of La0.7Ca0.3MnO3 thin films with improved oxygen content, crystallinity and magnetoresistive properties

Colossal magnetoresistive La0.7Ca0.3MnO3 (LCMO) films with improved magnetoresistance properties have been grown at relatively low temperatures using an ultraviolet-assisted pulsed laser deposition technique. In this technique, a low pressure Hg lamp having a fused silica envelope, which allows more than 85% of the emitted 184.9 nm radiation to be transmitted, is added inside the growth chamber during pulsed laser deposition of LCMO films. Magnetoresistance (MR) measurements carried out on LCMO films grown under identical conditions barring the presence/absence of UV radiation during thin film formation have shown that the MR ratio of UV-assisted grown LCMO films is nearly two orders of magnitude higher than that of LCMO films grown without UV. The improvement in magnetoresistive properties of LCMO film deposited in the presence of UV is assumed to be related with improvement in oxygen content, oxygen homogeneity, and crystallinity. Evidences supporting this assumption are obtained from analysis of spectra recorded using x-ray photoelectron spectroscopy and Rutherford backscattering measurements.

Low-temperature growth of high-k thin films by ultraviolet-assisted pulsed laser deposition

Medium- and high-k dielectric films were grown directly on Si by ultraviolet-assisted pulsed laser deposition (UVPLD). It has been found that at the interface between the dielectric and Si, SiO2 layers of various thickness were always formed. The source for this interfacial layer formation could be the physisorbed oxygen trapped inside the growing dielectric layer during the ablation process. When trying to reduce the thickness of this low-k SiO2 layer, a marked decrease in the electrical properties was noticed. The dielectric constant of 50nm thick barium strontium titanate (BST) thin films deposited at 600°C was around 180 while the leakage current density was below 1×10−5A/cm2 at +1.0V.

Ultraviolet-assisted pulsed laser deposition of thin oxide films

The properties of thin Y2O3, ZnO, and Ba0.5Sr0.5TiO3 films grown using an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better structural, optical, and electrical properties, especially for lower substrate temperatures. These improvements can be explained by the combined action of several processes. First, high energy UV photons and ozone ensure a better in situ cleaning of the substrate prior to the deposition. Second, the presence of ozone and atomic oxygen formed by photodissociation of molecular O2 promotes the growth of more oxygenated films. Finally, absorption of UV photons by adatoms could result in an increase of their surface mobility. All these factors have a beneficial effect upon crystalline growth.

Room temperature growth of indium tin oxide thin films by ultraviolet-assisted pulsed laser deposition

Thin indium tin oxide (ITO) films were grown at room temperature on (100) Si and Corning glass by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique. The oxygen pressure during the growth markedly influenced the properties of the films. For oxygen pressure below 1mTorr, films exhibited very low optical transmittance and high resistivity. The resistivity decreased when using higher oxygen pressures while the optical transmittance increased. For a target–substrate distance of 10.5cm, the optimum oxygen pressure was found to be around 10mTorr. For higher oxygen pressures, the optical transmittance was higher but a rapid increase of the electrical resistivity was noticed. X-ray photoelectron spectroscopy showed that ITO films grown at 10mTorr were fully oxidized. All grown films were amorphous regardless of the oxygen pressure used.

Characteristics of the surface layer of barium strontium titanate thin films deposited by laser ablation

Ba 0.5 Sr 0.5 TiO 3 (BST) thin films grown on Si by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique exhibited significantly higher dielectric constant and refractive index values and lower leakage current densities than films grown by conventional PLD under similar conditions. X-ray photoelectron spectroscopy (XPS) investigations have shown that the surface layer of the grown films contained, besides the usual BST perovskite phase, an additional phase with Ba atoms in a different chemical state. PLD grown films always exhibited larger amounts of this phase, which was homogeneously mixed with the BST phase up to several nm depth, while UVPLD grown films exhibited a much thinner (∼1 nm) and continuous layer. The relative fraction of this phase was not correlated with the amount of C atoms present on the surface. Fourier transform infrared spectroscopy did not find any BaCO3 contamination layer, which was believed to be related to this new phase. X-ray diffraction measurement showed that although PLD grown films contained less oxygen atoms, the lattice parameter was closer to the bulk value than that of UVPLD grown films. After 4 keV Ar ion sputtering for 6 min, XPS analysis revealed a small suboxide Ba peak for the PLD grown films. This finding indicates that the average Ba–O bonds are weaker in these films, likely due to the presence of oxygen vacancies. It is suggested here that this new Ba phase corresponds to a relaxed BST surface layer.

Low Temperature Growth Of Barium Strontium Titanate Films By Ultraviolet-Assisted Pulsed Laser Deposition

AbstractBarium strontium titanate (BST) thin films were grown directly on Si substrates by an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique. With respect to films grown by conventional (i.e. without UV illumination) pulsed laser deposition (PLD), the UVPLD grown films exhibited improved structural and electrical properties. The dielectric constant of a 40-nm thick film deposited at 650 °C was determined to be 281, the leakage current density was approximately 4×10−8 A/cm2at 100 kV/cm, and the density of interface states at the flat-band voltage was found to be approximately 5.6×1011 eV−1 cm−2 X-ray photoelectron spectroscopy investigations found that the surface of the grown films exhibited an additional Ba-containing phase, besides the usual BST perovskite phase, which was likely caused by stress and/or oxygen vacancies. The amount of this new phase was always smaller and very superficial for UVPLD grown films, which can explain their better overall properties.

Characteristics of Ultra violet-Assisted Pulsed Laser Deposited Thin Oxide Films

AbstractThe properties of thin oxide films such as Y2O3, ZnO and Ba0.5Sr0.5TiO3 grown using an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better structural and optical and electrical properties, especially for lower substrate temperatures. They also exhibited a better stoichiometry and contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be traced to several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate prior to the deposition. Secondly, the presence of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular O2 promotes the growth of more oxygenated films. Thirdly, absorption of UV photons by adatoms could result in an increased of their surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures. For optimised growth conditions, the crystalline quality and properties of ultraviolet-assisted pulsed laser deposited films was similar to that of films grown using conventional PLD at substrate temperatures of at least 200°C higher.

Room Temperature Growth of Indium Tin Oxide Films By Ultraviolet-Assisted Pulsed Laser Deposition

AbstractThe characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Coming glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.

Room Temperature Growth of Indium Tin Oxide Films by Ultraviolet-Assisted Pulsed Laser Deposition

AbstractThe characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Corning glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.

Characteristics of Ba 0.5 Sr 0.5 TiO 3 thin films grown by ultraviolet-assisted pulsed laser deposition

The microstructure and properties of barium strontium titanate (BST) thin films grown by an in situ ultraviolet-assisted (UV-assisted) pulsed laser deposition (UVPLD) technique are reported in this paper. In comparison with BST films grown by conventional pulsed laser deposition (PLD) under similar conditions, but without UV illumination, the UVPLD-grown films exhibited improved structural, electrical, and optical properties. X-ray photoelectron spectroscopy showed that when exposed to atmosphere, Ba atoms from the outermost layers formed a thin layer of barium carbonate, which negatively affects the film electrical characteristics. UVPLD-grown films exhibited a smaller amount of Ba atoms within the carbonate layer, resulting in better electrical characteristics. The dielectric constant of 40-nm-thick films deposited at 650 °C by UVPLD and PLD were determined to be 281 and 172, respectively. The leakage current density of the UVPLD-grown films was in the mid-10-8 A/cm2 range, a factor of 2 lower than that obtained from PLD-grown films.

Low-temperature growth of epitaxial ZnO films on (001) sapphire by ultraviolet- assisted pulsed laser deposition

ZnO thin films have been grown on thin Si3N4 membranes and (001) sapphire substrates by an ultraviolet-assisted pulsed laser deposition (UVPLD) technique. The microstructure of the films grown on Si3N4 membranes, investigated by transmission electron microscopy, showed that crystalline and textured films can be grown by UVPLD at a substrate temperature of only 100 °C. For deposition temperatures higher than 400 °C, ZnO films grown on sapphire substrates were found to be epitaxial by Rutherford backscattering (RBS) and X-ray diffraction measurements. The minimum yield of channeling RBS spectra recorded from films deposited at 550 °C was around 2% and the FWHM of the rocking curve for the (002) diffraction peak was 0.17°; these values are similar to those recorded from ZnO layers grown by conventional PLD at 750 °C.

Low-temperature growth of Y 2 O 3 thin films by ultraviolet-assisted pulsed laser deposition

Thin Y2O3 films have been grown on (100) Si using an in-situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique. When compared to conventional pulsed laser deposited (PLD) films under similar conditions, the UVPLD-grown films exhibited better structural and optical properties, especially those grown at lower substrate temperatures, from 200 °C to 400 °C. X-ray diffraction investigations showed that the films grown were highly crystalline and textured. According to X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry investigations, UVPLD-grown Y2O3 films have a better overall stoichiometry and contain less physisorbed oxygen than the conventional PLD-grown films. The refractive index values, measured in the range 300–750 nm by using variable-angle spectroscopic ellipsometry, were similar to those of a reference Y2O3 film.

Enhanced electrical properties of Ba0.5Sr0.5TiO3 thin films grown by ultraviolet-assisted pulsed-laser deposition

In this letter, we report enhanced electrical performance of high-dielectric-constant barium strontium titanate (BST) thin films grown by an in situ ultraviolet (UV)-assisted pulsed-laser deposition (UVPLD) technique. In comparison with conventional pulsed-laser deposition (PLD) BST (i.e., films grown under similar conditions but without UV illumination) and films grown by other techniques, the UVPLD-grown films exhibited improved structural and electrical properties. The dielectric constant of 40-nm-thick films deposited at 650 °C by PLD and UVPLD were determined to be 172 and 281, respectively. The density of interface states at the flat-band voltage was found to be approximately 5.6×1011 eV−1 cm−2 for the UVPLD-grown BST films, which was almost an order of magnitude lower than that obtained for conventional PLD films. The leakage current density of the UVPLD-grown films was approximately 4×10−8 A/cm2 at 100 kV/cm, which was nearly 1.5 times lower than that obtained from the PLD deposited films. The equivalent silicon dioxide thickness of the best BST films grown was found to be around 10 Å.

Ultraviolet Assisted Pulsed Laser Deposition of Thin Oxide Films

AbstractThe properties of Y2O3, ITO (indium tin oxide), and TaSi2 thin layers grown using a new in-situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. X-ray diffraction investigations showed that with respect to conventional PLD grown films under similar conditions, but without UV illumination, UVPLD grown films exhibited better crystallinity, especially for growth at low substrate temperatures, from 200 °C up to 450 °C, depending on the material. X-ray photoelectron spectroscopy investigations showed that UVPLD layers contained less physisorbed oxygen than the conventional PLD layers, exhibiting a better overall stoichiometry. These results suggest that during the ablation-growth process, UV radiation increases the surface mobility of adatoms and provides more reactive gaseous species. Both factors contribute to the crystalline growth and are especially effective at moderate processing temperatures, where the thermal energy available for the process is comparatively low.