Characterization of hexagonal ɛ-Ga1.8Sn0.2O3 thin films for solar-blind ultraviolet applications

Ga_1.8Sn_0.2O₃ thin films were deposited on c-plane Al₂O₃ (0001) substrates by laser molecular beam epitaxy technology. Well crystallized (002) oriented ɛ-phase Ga_1.8Sn_0.2O₃ thin films were obtained at the substrate temperature above 750 °C and the oxygen partial pressure more than 5 × 10⁻³ Pa. The band-gap slightly shrinks with Sn⁴⁺ ions incorporated into Ga³⁺ sites, showing an excellent solar-blind ultraviolet (UV) characteristic. The conductivity of hexagonal ɛ-Ga_1.8Sn_0.2O₃ films is very low in the dark, and permitting the design and fabrication of solar-blind photodetector. The photodetector exhibits obvious photo-response under 254 nm UV light irradiation, and it increases in photocurrent with both the rise of applied bias and optical input power. The results suggest that ɛ-Ga_1.8Sn_0.2O₃ thin film is a promising candidate for using in solar-blind photodetectors.     

Preparation and characterization of Sn-doped β-Ga2O3 homoepitaxial films by MOCVD

Journal of Materials Science - Sn-doped gallium oxide (Ga2O3:Sn) films were deposited on β-Ga2O3 (100) substrates by metal organic chemical vapor deposition method. The Sn concentration was...     

Growth characteristics and device properties of MOD derived β-Ga2O3 films

β-Ga₂O₃ films prepared by metal organic deposition (MOD) on (000l) sapphire substrates, have been developed for ultraviolet photodectors. The structural, surface, optical properties of MOD derived β-Ga₂O₃ films depending on growth temperatures were investigated. As growth temperature increased, the crystallinity of β-Ga₂O₃ films enhanced, crystallite size and surface roughness increased. The optical band gap of β-Ga₂O₃ films maintained within 4.8–4.9 eV at different growth temperatures. Metal–semiconductor–metal ultraviolet photodetectors based on MOD derived β-Ga₂O₃ films were successfully fabricated, demonstrating the responsivity of 0.76 A/W at 20 V and the upper limits of the rise and decay time of 50 and 30 ms, respectively, indicating a promising low-cost approach for Ga₂O₃-base photoelectronics applications.     

Characterization of β-Ga2O3 films deposited under different growth temperature by pulsed laser deposition

Journal of Materials Science: Materials in Electronics - A series of β-Ga2O3 films were prepared on polished Al2O3 substrates by pulsed laser deposition at temperatures between 580 and 780...     

Moiré patterns and their application to the study of the growth of YBa2Cu3O7-δ thin films

Very thin films of YBa₂Cu₃O_7- have been formed directly on specially prepared electron-transparent thin-foil substrates of MgO by pulsed-laser deposition and examined using transmission electron microscopy. The moiré fringe pattern visible in the electron micrographs has been used to provide information about film growth and the introduction of defects into the growing film. Individual domains, rotated about the [001] zone axis by small amounts, were detectable in the moiré fringe pattern by rotation of the fringes. In the case of small rotations, the fringe spacing varies only slightly. Individual domains rotated by large amounts, about the [001] zone axis, have been identified by the large variation produced in the moiré fringe spacing. The ability to identify domain rotation through examination of the moiré pattern is a very-fine-scale probe of local misorientations. Furthermore, these rotationally misaligned regions are formed directly at the film/substrate interface during the early stages of film growth. In some regions of the film, discontinuities in the moiré fringe pattern were observed. These discontinuities are indicative of growth-related defects, for example, threading dislocations. It was found that the number density of these defects was apparently reduced in films grown at higher substrate temperatures.     

Structural,optical and electrical properties of Bi2−xMnxTe3 thin films

Journal of Materials Science: Materials in Electronics - Undoped and Mn doped Bi2Te3 (x = 0, 0.05 and 0.10 at%) thin films were prepared via thermal evaporation method from their bulk alloys. X-ray...     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

Structural and electronic characteristics of Fe-doped β-Ga2O3 single crystals and the annealing effects

Journal of Materials Science - As capture traps, Fe impurities were intentionally incorporated into beta-gallium oxide (β-Ga2O3) crystals to compensate for unintentional n-type conductivity...     

Dielectric behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO3 composites

Thin films of the composites formed between poly(vinylidene fluoride) (PVDF) and lead zirconium titanate (PZT) and also barium titanate with 0–3 connectivity, have been obtained by dispersion of the ceramic powder in a solution of PVDF in dimethylacetamide DMA. Evaporation of the solvent at 65 °C allowed crystallization of PVDF predominantly in the polar phase, regardless of the amount of PZT or BaTiO₃ powder added upto 40 vol %. The relative permittivity and loss index values were determined for the pure components and for the composites with different ceramic contents, in the frequency range of 100 Hz to 13 MHz. An increase in PZT or BaTiO₃ content resulted in an increase in the relative permittivity of the composites, and the experimental results are shown to be in good agreement with those calculated from the theoretical expression of Yamada et al. [1]. The de electrical conductivity of composites with different compositions was also determined.     

Synthesis of β-Mo(2)C thin films

Thin films of stoichiometric β-Mo(2)C were fabricated using a two-step synthesis process. Dense molybdenum oxide films were first deposited by plasma-enhanced chemical vapor deposition using mixtures of MoF(6), H(2), and O(2). The dependence of operating parameters with respect to deposition rate and quality is reviewed. Oxide films 100-500 nm in thickness were then converted into molybdenum carbide using temperature-programmed reaction using mixtures of H(2) and CH(4). X-ray diffraction confirmed that molybdenum oxide is completely transformed into the β-Mo(2)C phase when heated to 700 °C in mixtures of 20% CH(4) in H(2). The films remained well-adhered to the underlying silicon substrate after carburization. X-ray photoelectron spectroscopy detected no impurities in the films, and Mo was found to exist in a single oxidation state. Microscopy revealed that the as-deposited oxide films were featureless, whereas the carbide films display a complex nanostructure.     

Effect of annealing on optical properties of thin films with β-FeSi2 quantum dots

Reactive deposition epitaxy was used to prepare β-FeSi₂ nanodots on a Si(001) surface. The influence of annealing on optical properties has been studied. Annealing increases the particle size and decreases absorption. The indirect optical transition at 0.84-0.89 eV dominates the absorption spectra below 1.3-1.5 eV. The film with smaller nanoparticles exhibits higher absorption with direct optical transition energies in the 1.3-1.5 eV range. It suggests that direct transition is dominant only in small (around 3 nm diameter) β-FeSi₂ nanodots. Larger particles are dominated by the indirect optical transition.     

Synthesis,structure, and optical properties of Au–TiO2 composite thin films

Titanium dioxide (TiO₂) films with varying concentrations of gold particles were synthesized using pulsed DC magnetron sputtering, with the intent to develop infrared reflecting films for use on cars and planes to reduce solar heat load. Under our deposition conditions, the films are smooth (RMS roughness on the order of 1.0–2.0 nm) and consist of rutile TiO₂ with embedded gold. The average gold particle diameter on the sample surface was found to change from 60 to 200 nm as the volume fraction of gold in the films increased from 1.9 to 4.3% (3.5 to 7.9 mol% Au). The maximum reflectance of these films in the infrared region (800–2500 nm) is > 50%, compared with 30% for pure TiO₂. The Maxwell–Garnett equation does not model the reflectance data very well, due to the relatively large gold particle size. Instead, by assuming that the contribution of gold particles to the reflectance response is proportional to their projected areal fraction in an effective medium approximation, we were able to fit the observed reflectance data quite well.     

Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Growth, electrical and structural characterization of β-GaSe thin films

GaSe thin films were deposited onto the glass substrates kept at 200° and 300°C by the thermal evaporation of GaSe crystals under the pressure of 10^–5 Torr. X-ray analysis of the films revealed that films grown at 200°C are amorphous in nature while the films grown at 300°C are polycrystalline -GaSe. The temperature dependent electrical conductivity measurements in the region of 320–100 K for the films grown at 300°C showed that the transport mechanisms are the thermionic emission of charged carriers and the variable range hopping above and below 180 K, respectively. Space charge limited current (SCLC) studies have also been performed on these films through the current-voltage measurements at different temperatures and a dominant hole trap at 0.233 eV from the top of the valance band with a trap density of 1.6 × 10¹¹ cm^–3 is identified.     

Growth and characterization of ceria thin films and Ce-doped γ-Al2O3 nanowires using sol-gel techniques

γ-Al(2)O(3) is a well known catalyst support. The addition of Ce to γ-Al(2)O(3) is known to beneficially retard the phase transformation of γ-Al(2)O(3) to α-Al(2)O(3) and stabilize the γ-pore structure. In this work, Ce-doped γ-Al(2)O(3) nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500?°C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped γ-Al(2)O(3) nanowires. Ce(3+) ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO(2) thin film was deposited with a cubic fluorite structure and a crystallite size of 6-7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al(2)O(3) nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements.