Alloying behavior of gold,Au-Ge and Au-Ge-Ni on GaAs

The alloying behavior of gold, Au-Ge and Au-Ge-Ni films on GaAs has been studied after furnace annealing at 350 °C, 425 °C and 450 °C for 15 min, 0.5 min and 15 min respectively. Rutherford backscattering reveals that gold from Au-Ge films diffuses into the GaAs at a much lower temperature than that from gold and Au-Ge-Ni films. Transmission electron microscopy analysis reveals the presence of β-Ga₂O₃ in the 450 °C annealed specimens. In addition to this, the presence of Au₇Ga₂ and metastable γ-(Au-Ge) phases was identified in annealed Au-Ge films. Scanning electron micrographs of annealed samples show black patches which were found to be gold deficient compared with the light-gray areas. The surface morphology of Au-Ge-Ni films after alloying is more uniform than that of Au-Ge films.     

In situ X-ray diffraction study of the effects of germanium and nickel concentrations on melting in gold-based contacts to gallium arsenide

Using X-ray diffraction in situ at 1 atm, the melting of the as-deposited film and the formation of the reaction product was investigated for gold, Au-Ge and Au-Ge-Ni contacts with various germanium and nickel concentrations. For the Au-Ge contact, the melting temperature of the as-deposited film was found to be 512±12 °C, 486±13 °C, 363±12 °C, and 363±12 °C with germanium concentrations of 0 wt.%, about 0.6 wt.%, 3 wt.% and 12 wt.% respectively. For the Au-Ge-Ni contacts, the melting temperature of the as-deposited film was 363±12 °C, 363±12 °C and 413±11 °C with germanium concentrations in the range 10–12 wt.% and nickel concentrations of 0 wt.%, 4 wt.% and 17 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₇Ga₂ formed in Au-Ge contacts with 0–3 wt.% Ge and it melted on second heating at 405±5 °C, 387±18 °C and 337±12 °C for germanium concentrations of 0 wt.%, about 0.6 wt.% and 3 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₂Ga formed in Au-Ge contacts with 12 wt.% Ge and Au-Ge-Ni contacts; Au₂Ga melted on second heating at 363±12 °C for Au-Ge-Ni contacts with 12 wt.% Ge and 4 wt.% Ni, and at 413±11 °C for Au-Ge-Ni contacts with 10 wt.% Ge and 17 wt.% Ni. Hence germanium decreased the melting temperatures of α-AuGa (gold-rich solid solution) and Au₇Ga₂ because of the presence of dissolved germanium in these phases. In addition, nickel increased the melting temperature of α-AuGa (gold-rich solid solution) and Au₂Ga owing to the presence of dissolved nickel in these phases.     

Embedding of reduced pressure-chemical vapor deposition grown Ge nanocrystals in a high quality SiO2 matrix for non-volatile memory applications

We have obtained thanks to reduced pressure-chemical vapor deposition germanium nanocrystals in a high quality SiO₂ matrix. A perfect control of (i) the tunnel and control oxide layer thicknesses and (ii) the germanium nanocrystals' density and diameter has been achieved. Scanning electron microscopy was used to (i) determine the nucleation and growth rate of the germanium nanocrystals and (ii) evaluate their morphological stability during their embedding. We have also studied the influence of thin selectively grown Si films in order to passivate the surface of the germanium nanocrystals. X-ray photoelectron spectroscopy has shown that the germanium nanocrystals' surface properties are better with a Si capping. The polycrystalline state of the nanocrystals has been evaluated with X-ray diffraction. Transmission electron microscopy image reveals the lack of germanium diffusion and precipitation in the SiO₂ matrix.     

Dielectric enhancement of the trilayered Bi3.15Eu0.85Ti3O12/Bi3.15Nd0.85Ti3O12/Bi3.15Eu0.85Ti3O12 thin film deposited on Pt/Ti/SiO2/Si substrate

The trilayered Bi_3.15Eu_0.85Ti₃O₁₂/Bi_3.15Nd_0.85Ti₃O₁₂/Bi_3.15Eu_0.85Ti₃O₁₂ (BET/BNT/BET) thin film was deposited on Pt/Ti/SiO₂/Si(100) substrates by metal organic decomposition at annealing temperature of 650 °C, and the microstructure, chemical composition, leakage current, dielectric and ferroelectric properties were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, semiconductor characterization system, impedance analyzer and ferroelectric tester. The trilayered thin film is of crack-free and dense surface with some discrete cluster distribution, and typical Bi-layered perovskite polycrystalline phase. The dielectric constant ε _r and dissipation factor tanδ are 1,233 and 0.0215 at 100 kHz for the trilayered thin film. Comparing with the pure BET and BNT thin films, the dielectric constant of trilayered thin film is enhanced, which is due to the space charge and the intermediate superlattice. The trilayered thin film shows excellent dielectric properties and can be promisingly used for the high dielectric layer of silicon-based embedded capacitors in package substrate.     

Enhanced photoluminescence of CaTiO3:Pr phosphor films deposited on SiO2 buffered Si substrates

CaTiO₃:Pr³⁺ films have been prepared by pulsed-laser deposition method on SiO₂-buffered Si substrates, and their microstructure and photoluminescence properties have been compared with those of the films deposited directly on bare Si substrates. The SiO₂ buffer layers were prepared using thermal oxidization and HF-etching. Photoluminescence intensities of CaTiO₃:Pr³⁺ films on the SiO₂-buffered Si substrates are significantly higher (up to 800%) than those of the films on bare Si substrates, which is attributed to the low refractive index and low light absorption of the SiO₂ buffer layer. This study reveals that the presence of the buffer layer is effective in improving the red emission brightness of CaTiO₃:Pr³⁺ films without sacrificing the surface roughness.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Deuterium trapping in iron alloys formed by ion implantation

The main results of several years' work on MIS structures based on germanium are presented. We studied the properties of the interfaces between germanium and germanium dioxide, germanium and silicon dioxide, germanium and silicon nitride and also germanium and double-layer SiO₂Si₃N₄ dielectric films. The main electrophysical characteristics of the various interfaces were compared bearing in mind the techniques of their fabrication. The important role of carriers tunnelling into traps is described. The characteristics of a germanium MIS transistor are discussed and the structural defects of the interfaces and their effect on the electrophysical characteristics of the transistor are briefly considered.     

Properties of indium tin oxide films deposited on unheated polymer substrates by ion beam assisted deposition

The optical, electrical and mechanical properties of indium tin oxide (ITO) films prepared on polyethylene terephthalate (PET) substrates by ion beam assisted deposition at room temperature were investigated. The properties of ITO films can be improved by introducing a buffer layer of silicon dioxide (SiO₂) between the ITO film and the PET substrate. ITO films deposited on SiO₂-coated PET have better crystallinity, lower electrical resistivity, and improved resistance stability under bending than those deposited on bare PET. The average transmittance and the resistivity of ITO films deposited on SiO₂-coated PET are 85% and 0.90 × 10^− 3 Ω cm, respectively, and when the films are bent, the resistance remains almost constant until a bending radius of 1 cm and it increases slowly under a given bending radius with an increase of the bending cycles. The improved resistance stability of ITO films deposited on SiO₂-coated PET is mainly attributed to the perfect adhesion of ITO films induced by the SiO₂ buffer layer.     

Spectrographic ellipsometry study of a liquid crystal display substrate consisting of thin films of SiO2, polyimide and indium tin oxide on glass

Variable angle spectrometric ellipsometry at room temperature is used to determine thin film parameters of substrates used in liquid crystal displays. These substrates consist of sequential thin films of polyimide (PI), on indium tin oxide (ITO),on SiO₂ deposited on a glass backing approximately 1.1 mm thick. These films were studied by sequentially examining more complex systems of films (SiO₂, SiO₂-ITO, SiO₂-ITO-PI). The SiO₂ layer appears to be optically uniform and flat. The ITO film is difficult to characterize. When this surface film's lower surface is SiO₂ and upper surface is an air-ITO-interface it is found that including surface roughness and variation of the optical properties with ITO thickness in the model improved the fit; suggesting that both phenomena exist in the ITO films. However, the surface roughness and graded nature of optical properties could be not determinable by ellipsometry when the ITO is coated with a polyimide film. The PI films are ellipsometrically flat and over the wavelength range from 500 to 1400 nm the real refractive index of polyimide films varying in thickness between 25 and 80 nm is well modeled by a two-term Cauchy model with no absorption. The ellipsometric thickness of the ITO layer is the same as the profilometric thickness; however, the ellipsometric thickness of the polyimide layers is roughly 10 nm larger than that obtained from the profilometer. These final observations are consistent with the literature.     

Kinetics of interfacial layer formation during deposition of HfO2 on silicon

Very thin HfO₂ films were deposited directly on Si substrates by the pulsed laser deposition technique in a wide range of substrate temperatures and oxygen pressures to investigate the kinetics of the interfacial layer formation. Angle-resolved X-ray photoelectron spectroscopy (XPS) investigations showed that the interfacial layer formed between the Si substrate and the deposited oxide contains a mixture of HfO₂ and SiO₂ without any strong evidence to support the formation of a silicate-type compound. X-Ray reflectivity measurements showed that the mass density of the interfacial layer is higher than that of pure SiO₂, while spectroscopic ellipsometry measurements showed that the refractive index is higher than that of pure SiO₂, therefore corroborating the XPS results.     

Effect of barrier layers on the properties of indium tin oxide thin films on soda lime glass substrates

In this paper, the electrical, structural and optical properties of indium tin oxide (ITO) films deposited on soda lime glass (SLG) haven been investigated, along with high strain point glass (HSPG) substrate, through radio frequency magnetron sputtering using a ceramic target (In₂O₃:SnO₂, 90:10 wt.%). The ITO films deposited on the SLG show a high electrical resistivity and structural defects compared with those deposited on HSPG due to the Na ions from the SLG diffusing to the ITO film by annealing. However, these properties can be improved by intercalating a barrier layer of SiO₂ or Al₂O₃ between the ITO film and the SLG substrate. SIMS analysis has confirmed that the barrier layer inhibits the Na ion's diffusion from the SLG. In particular, the ITO films deposited on the Al₂O₃ barrier layer, show better properties than those deposited on the SiO₂ barrier layer.     

The role of SiO2 buffer layer in the growth of highly textured LiNbO3 thin film upon SiO2/Si by pulsed laser deposition

Highly c-axis-oriented lithium niobate (LiNbO₃) thin films have been grown on Si with optimum thickness of the SiO₂ buffer layer by pulsed laser deposition technique. The amorphous SiO₂ buffer layer was formed on Si (100) wafer by thermal oxidation method. The crystallinity and c-axis orientation of LiNbO₃ films were strongly influenced by the thickness of amorphous SiO₂ buffer layers. The optimum thickness of the amorphous SiO₂ buffer layer was found to be about 230 nm for the growth of highly c-axis-oriented LiNbO₃ films. The achieved films have smooth surface and sharp interface. The prism coupler method indicates that the prepared LiNbO₃ films have great potential for optical waveguide device.     

Dielectric properties of (Ba,Ca)(Zr,Ti)O3/CaRuO3 heterostructure thin films prepared by pulsed laser deposition

(Ba_0.90Ca_0.10)(Zr_0.25Ti_0.75)O₃ (BCZT) thin films were grown on Pt/Ti/SiO₂/Si substrates without and with a CaRuO₃ (CRO) buffer layer using pulsed laser deposition (PLD). The structure and surface morphology of the films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At room temperature and 1 MHz, the dependence of dielectric constant and tunability of the films with electric field were investigated; the dielectric constant and tunability are 725 and 47.0%, 877 and 50.4%, respectively, for the BCZT film on Pt/Ti/SiO₂/Si substrates without and with the CRO buffer layer at 400 kV/cm. The tunability of the BCZT/CRO heterostructure thin films on Pt/Ti/SiO₂/Si substrates was higher than that of the BCZT thin films on Pt/Ti/SiO₂/Si substrates. The high constant likely results from the oxide electrode (CRO).     

Thin magnetite films on an oxidized silicon surface: Raman spectroscopy study

Polycrystalline films of magnetite (Fe₃O₄) formed by the reactive sputtering of iron in oxygen on Si(001) substrates covered by thin (1.4 nm) or thick (1200 nm) SiO₂ layers have been studied by Raman spectroscopy. It is established that (i) the α-Fe₂O₃ phase is formed due to the laser-induced heating in magnetite films synthesized on thick SiO₂ layers and (ii) the formation of α-Fe₂O₃ phase depends on the thickness of the buffer SiO₂ layer.     

Blue-shifted stimulated emission from ZnO films deposited on SiO2 by atomic layer deposition

ZnO films were prepared by atomic layer deposition upon a SiO₂ layer on a Si substrate and treated by rapid thermal annealing. The optically-pumped random lasing actions with low threshold values were observed in the ZnO films on SiO₂/Si substrates. With the decrease in ZnO film thickness or the increase in post-annealing duration, the stimulated emission shifted toward the shorter wavelength and the lasing threshold increased. The results can be attributed to the inter-diffusion between ZnO and SiO₂, which causes the modification of bandgap renormalization in ZnO.     

The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films prepared by RF magnetron sputtering

(Ba_{1 − x} Sr _x )TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering. The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy and dielectric frequency spectra. It was found that the preferred orientation of BST thin films could be tailored by insertion of YSZ interlayer and adjusting the thickness of YSZ interlayer. The BST thin films deposited on YSZ interlayer exhibited a more compact and uniform grain structure than that deposited directly on Pt electrode. Dielectric measurement revealed that the BST thin films deposited on 10 nm YSZ interlayer have the largest dielectric constant and a low dielectric loss tangent. The enhanced dielectric behavior is mainly attributed to the YSZ interlayer which serves as an excellent seeding layer to enhance the crystallization of subsequent BST films layer, and a smaller thermal stress field built up at the interface between YSZ interlayer and BST film layer.     

Enhanced effect of vacuum-deposited SiO2 overlayer on photo-induced hydrophilicity of TiO2 film

Photo-induced hydrophilicity of SiO₂/TiO₂ multilayer film prepared by using the vacuum deposition method was investigated by means of water contact angle measurement. Using black light irradiation of the films centering at a wavelength of 365 nm, an extreme photo-induced hydrophilicity was achieved when the TiO₂ film was covered by SiO₂ overlayer ranging from 10 to 20 nm in thickness. These multilayer films exhibited much more extreme hydrophilicity than the TiO₂ film without SiO₂ overlayer. The surface analyses revealed that the enhanced photo-induced hydrophilic surface of the multilayer films exhibited an improved photo-catalytic activity towards decomposition of organic substances on their surfaces. It was found that significant growth of the SiOH group occurred in the uppermost surface of the SiO₂ overlayer of the multilayer films through the depth profile measurement of TOF-SIMS. This result suggests that the photo-generated reactive species such as hole created in the TiO₂ film may transmit the SiO₂ layer to reach the surface. The enhanced photo-induced hydrophilicity of the films can be explained by a synergetic effect of the improved photo-catalytic activity of the multilayer film and the stable hydrophilicity of SiO₂ itself.     

Effect of the interface on the electrical properties of an indium zinc oxide/SiOx multilayer

In this work, indium zinc oxide (IZO) films have been deposited on a polyethylene terephthalate substrate coated with an SiO_x film. Based on a comparative investigation of an IZO monolayer and an IZO/SiO_x multilayer, it is shown that oxygen has a great effect on the electrical properties of the thin films. A mechanism is described to explain the influence of the introduced SiO_x buffer layer. It is considered that an interfacial layer has come into being at the interface between the SiO_x layer and IZO layer, and the properties of this layer have been evaluated. Moreover, the electrical properties of the IZO/SiO_x multilayer have been successfully improved by controlling the oxygen content of the interfacial layer.     

Evolution of SiO2/Ge/HfO2(Ge) multilayer structure during high temperature annealing

Use of germanium as a storage medium combined with a high-k dielectric tunneling oxide is of interest for non-volatile memory applications. The device structure consists of a thin HfO₂ tunneling oxide with a Ge layer either in the form of continuous layer or discrete nanocrystals and relatively thicker SiO₂ layer functioning as a control oxide. In this work, we studied interface properties and formation kinetics in SiO₂/Ge/HfO₂(Ge) multilayer structure during deposition and annealing. This material structure was fabricated by magnetron sputtering and studied by depth profiling with XPS and by Raman spectroscopy. It was observed that Ge atoms penetrate into HfO₂ layer during the deposition and segregate out with annealing. This is related to the low solubility of Ge in HfO₂ which is observed in other oxides as well. Therefore, Ge out diffusion might be an advantage in forming well controlled floating gate on top of HfO₂. In addition we observed the Ge oxidation at the interfaces, where HfSiO_x formation is also detected.     

SiO2 layer thickness effects on the (001) texture of FePtCu:SiO2 nanocomposite films

The influence of SiO₂ layer thickness of (Fe₅₂Pt₄₈)₈₈Cu₁₂:SiO₂ multilayer nanocomposite films on their structural and magnetic properties were investigated. The films were deposited on (001) textured FePt films, and then annealed at 873 K. The crystalline texture of (Fe₅₂Pt₄₈)₈₈Cu₁₂:SiO₂ films changes drastically with respect to the thickness of the SiO₂ layers. In the film with 50-Å thick SiO₂ layers, the (111) peak was strong although the (001) orientation is dominant, and self-organized spherical FePtCu particles were formed in the SiO₂ matrix. However, in the film with 19-Å thick SiO₂ layers, flat FePt grains with perfect (001) orientation were obtained. In addition, twins with different crystalline orientations were seen in the above films with different thicknesses of the SiO₂ layers. Accordingly, different perpendicular hysteresis loops were obtained.