Effects of substrate temperature on tin-doped indium oxide films deposited by dc arc discharge ion plating

Indium tin oxide (ITO) films were deposited on glass substrate at temperatures ranging from room temperature to 120 °C by the dc arc discharge ion plating technique. The electrical properties and crystallinity of ITO films were investigated. The resistivity of ITO films decreased with the increase of the substrate temperature in deposition, mostly due to increase in Hall mobility above 90 °C. The resistivity of ITO film obtained at temperature 120 °C was 1.33×10⁻⁴ Ω cm. The ITO films crystallized at the substrate temperature higher than 90 °C and the grain size estimated from the (2 2 2) peak in the direction parallel to the surface of the substrate became large with the increase of the substrate temperature. That the Hall mobility increased with the increase of the substrate temperature was speculated to be due to the increase of the grain size in the direction parallel to the surface.     

The effects of substrate temperature on the structure and properties of ZnO films prepared by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition (PLD) on glass substrates with growth temperature from room temperature (RT) to 500 °C. The effects of substrate temperature on the structural and optical properties of ZnO films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra, and RT photoluminescence (PL) measurements. The results showed that crystalline and (0 0 2)-oriented ZnO films were obtained at all substrate temperatures. As the substrate temperature increased from RT to 500 °C, the ratio of grain size in height direction to that in the lateral direction gradually decreased. The same grain size in two directions was obtained at 200 °C, and the size was smallest in all samples, which may result in maximum E_g and E₀ of the films. UV emission was observed only in the films grown at 200 °C, which is probably because the stoichiometry of ZnO films was improved at a suitable substrate temperature. It was suggested that the UV emission might be related to the stoichiometry in the ZnO film rather than the grain size of the thin film.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

Growth of stoichiometric TiO2 thin films on Au(100) substrates by molecular beam epitaxy

The present study reports on the growth of thin TiO₂ films onto Au(100) single crystals by Ti evaporation in a reactive O₂ atmosphere at two different substrate temperatures: room temperature (RT) and 300 °C. The growth of the oxide films was monitored by means of X-ray photoemission spectroscopy, while the valence and conduction band electronic structure was investigated by UV and inverse photoemission spectroscopy, respectively.The TiO₂ film grows epitaxially on the Au(100) substrate at 300 °C exhibiting the rutile (100) surface. The evolution of the Ti 2p lineshape with the oxide coverage shows the presence of reduced oxide species (characterized by Ti^3 + ions) at the Au(100) interface. A crystalline and stoichiometric TiO₂ oxide is produced at high substrate temperature, while growth at RT gives a measurable concentration of defects. Post growth annealing in ultra-high vacuum of the RT grown film increases this concentration, while subsequent annealing in O₂ atmosphere restores the sample to the as-grown conditions.     

Preparation and characterization of pulsed laser deposited CdTe thin films at higher FTO substrate temperature and in Ar + O2 atmosphere

Pulsed laser deposition (PLD) is one of the promising techniques for depositing cadmium telluride (CdTe) thin films. It has been reported that PLD CdTe thin films were almost deposited at the lower substrate temperatures (<300 °C) under vacuum conditions. However, the poor crystallinity of CdTe films prepared in this way renders them not conducive to the preparation of high-efficiency CdTe solar cells. To obtain high-efficiency solar cell devices, better crystallinity and more suitable grain size are needed, which requires the CdTe layer to be deposited by PLD at high substrate temperatures (>400 °C). In this paper, CdTe layers were deposited by PLD (KrF, λ = 248 nm, 10 Hz) at different higher substrate temperatures (T_s). Excellent performance of CdTe films was achieved at higher substrate temperatures (400 °C, 550 °C) under an atmosphere of Ar mixed with O₂ (1.2 Torr). X-ray diffraction analysis confirmed the formation of CdTe cubic phase with a strong (1 0 0) preferential orientation at all substrates temperatures on 60 mJ laser energy. The optical properties of CdTe were investigated, and the band gaps of CdTe films were 1.51 eV and 1.49 eV at substrate temperatures of 400 °C and 550 °C, respectively. Scanning electron microscopy (SEM) showed an average grain size of 0.3–0.6 μm. Thus, under these conditions of the atmosphere of Ar + O₂ (15 Torr) and at the relatively high T_s (500 °C), an thin-film (FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe: Cu/Ag) solar cell with an efficiency of 6.68% was fabricated.     

Fluorine-doped ZnO transparent conducting thin films prepared by radio frequency magnetron sputtering

Fluorine-doped ZnO transparent conducting thin films were prepared by radio frequency magnetron sputtering at 150 °C on glass substrate. Thermal annealing in vacuum was used to improve the optical and electrical properties of the films. X-ray patterns indicated that (002) preferential growth was observed. The grain size of F-doped ZnO thin films calculated from the full-width at half-maximum of the (002) diffraction lines is in the range of 18-24 nm. The average transmittance in visible region is over 90% for all specimens. The specimen annealed at 400 °C has the lowest resistivity of 1.86 × 10^− 3 Ω cm, the highest mobility of 8.9 cm² V^− 1 s^− 1, the highest carrier concentration of 3.78 × 10²⁰ cm^− 3, and the highest energy band gap of 3.40 eV. The resistivity of F-doped ZnO thin films increases gradually to 4.58 × 10^− 3 Ω cm after annealed at 400 °C for 4 h. The variation of the resistivity is slight.     

Synthesis of conductive semi-transparent silver films deposited by a Pneumatically-Assisted Ultrasonic Spray Pyrolysis Technique

The synthesis and characterization of nanostructured silver films deposited on corning glass by a deposition technique called Pneumatically-Assisted Ultrasonic Spray Pyrolysis are reported. Silver nitrate and triethanolamine were used as silver precursor and reducer agent, respectively. The substrate temperatures during deposition were in the range of 300–450 °C and the deposition times from 30 to 240 s. The deposited films are polycrystalline with cubic face-centered structure, and crystalline grain size less than 30 nm. Deposition rates up to 600 Å min⁻¹ were obtained at substrate temperature as low as 300 °C. The electrical, optical, and morphological properties of these films are also reported. Semi-transparent conductive silver films were obtained at 350 °C with a deposition time of 45 s.     

The effect of AlN buffer layer on properties of AlxIn1 − xN films on glass substrates

Al_xIn_1 − xN (AlInN) films with x = 0.36 and 0.55 were grown on glass substrate by pulsed direct-current reactive sputtering. X-ray photoelectron spectroscopy depth profiles revealed that oxygen diffused from glass substrate to AlInN films at temperatures ≧ 300 °C. After applying AlN buffer layer, the crystallinity of AlInN films was markedly improved without oxygen contamination observed. The AlN-buffered AlInN films are c-axis-oriented with low full-width-at-half-maximum of 2.9°-3.5°, fine-grained, and low electron concentration, which are comparable with AlInN films grown by other high-temperature processes. AlN buffer layer is proved to be good seeding and diffusion-barrier layers for AlInN films deposited on glass substrates.     

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.     

The effect of annealing on Al-doped ZnO films deposited by RF magnetron sputtering method for transparent electrodes

In this study, transparent conducting Al-doped zinc oxide (AZO) films with a thickness of 150 nm were prepared on Corning glass substrates by the RF magnetron sputtering with using a ZnO:Al (Al₂O₃: 2 wt.%) target at room temperature. This study investigated the effects of the post-annealing temperature and the annealing ambient on the structural, electrical and optical properties of the AZO films. The films were annealed at temperatures ranging from 300 to 500 °C in steps of 100 °C by using rapid thermal annealing equipment in oxygen. The thicknesses of the films were observed by field emission scanning electron microscopy (FE-SEM); their grain size was calculated from the X-ray diffraction (XRD) spectra using the Scherrer equation. XRD measurements showed the AZO films to be crystallized with strong (002) orientation as substrate temperature increases over 300 °C. Their electrical properties were investigated by using the Hall measurement and their transmittance was measured by UV-vis spectrometry. The AZO film annealed at the 500 °C in oxygen showed an electrical resistivity of 2.24 × 10^− 3 Ω cm and a very high transmittance of 93.5% which were decreased about one order and increased about 9.4%, respectively, compared with as-deposited AZO film.     

Substrate temperature dependence of the properties of Ga-doped ZnO films deposited by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. The influence of substrate temperature on the structural, electrical, and optical properties of ZnO:Ga films was investigated. The X-ray diffraction (XRD) studies show that higher temperature helps to promote Ga substitution more easily. The film deposited at 350 °C has the optimal crystal quality. The morphology of the films is strongly related to the substrate temperature. The film deposited is dense and flat with a columnar structure in the cross-section morphology. The transmittance of the ZnO:Ga thin films is over 90%. The lowest resistivity of the ZnO:Ga film is 4.48×10⁻⁴ Ω cm, for a film which was deposited at the substrate temperature of 300 °C.     

Growth and characterization of Bi2Se3 thin films by pulsed laser deposition using alloy target

Bi₂Se₃ thin films were deposited on the (100) oriented Si substrates by pulsed laser deposition technique at different substrate temperatures (room temperature −400 °C). The effects of the substrate temperature on the structural and electrical properties of the Bi₂Se₃ films were studied. The film prepared at room temperature showed a very poor polycrystalline structure with the mainly orthorhombic phase. The crystallinity of the films was improved by heating the substrate during the deposition and the crystal phase of the film changed to the rhombohedral phase as the substrate temperature was higher than 200 °C. The stoichiometry of the films and the chemical state of Bi and Se elements in the films were studied by fitting the Se 3d and the Bi 4d5/2 peaks of the X-ray photoelectron spectra. The hexagonal structure was seen clearly for the film prepared at the substrate temperature of 400 °C. The surface roughness of the film increased as the substrate temperature was increased. The electrical resistivity of the film decreased from 1 × 10⁻³ to 3 × 10⁻⁴ Ω cm as the substrate temperature was increased from room temperature to 400 °C.     

Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Deposition of Al-doped ZnO films on polyethylene naphthalate substrate with radio frequency magnetron sputtering

100 nm Al-doped ZnO (AZO) thin films were deposited on polyethylene naphthalate (PEN) substrates with radio frequency magnetron sputtering using 2 wt.% Al-doped ZnO target at various deposition conditions including sputtering power, target to substrate distance, working pressure and substrate temperature. When the sputtering power, target to substrate distance and working pressure were decreased, the resistivity was decreased due to the improvement of crystallinity with larger grain size. As the substrate temperature was increased from 25 to 120 °C, AZO films showed lower electrical resistivity and better optical transmittance due to the significant improvement of the crystallinity. 2 wt.% Al-doped ZnO films deposited on glass and PEN substrates at sputtering power of 25 W, target to substrate distance of 6.8 cm, working pressure of 0.4 Pa and substrate temperature of 120 °C showed the lowest resistivity (5.12 × 10^− 3 Ω cm on PEN substrate, 3.85 × 10^− 3 Ω cm on glass substrate) and high average transmittance (> 90% in both substrates). AZO films deposited on PEN substrate showed similar electrical and optical properties like AZO films deposited on glass substrates.     

Synthesis of V-doped TiO2 films by chemical bath deposition and the effect of post-annealing on their properties

Amorphous composite films, composed of a Ti_1 − xV_xO₂ solid-solution phase and a V₂O₅ phase, were produced by chemical bath deposition and subsequently air-annealed at various temperatures up to 550 °C. The microstructure and chemical composition of the as-prepared and annealed films were investigated by a combinatorial experimental approach using Scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Ultraviolet-Visible Spectrometry was applied to determine the optical band gap of the as-prepared and annealed films. It followed that the incorporation of vanadium in the as-deposited films reduces the optical band gap of TiO₂ from about 3.8 eV to 3.2 eV. Annealing of the films up to 350 °C leads to slight increase of band gap, as attributed to a reduction of the defect density in the initially amorphous oxide films due to the gradual development of long-range order and a concurrent reduction of the V⁴⁺-dopant concentration in the Ti_1 − xV_xO₂ solid-solution phase. The films crystallized upon annealing in air at 550 °C, which resulted in drastic changes of the phase constitution, optical absorbance and surface morphology. Due to the lower solubility of V⁴⁺ in crystalline TiO₂, V⁴⁺ segregates out of the crystallizing Ti_1 − xV_xO₂ solid-solution phase, forming crystalline V₂O₅ at the film surface.     

Deposition of silicon nitride thin films by hot-wire CVD at 100 °C and 250 °C

Silicon nitride thin films for use as passivation layers in solar cells and organic electronics or as gate dielectrics in thin-film transistors were deposited by the Hot-wire chemical vapor deposition technique at a high deposition rate (1-3 ?/s) and at low substrate temperature. Films were deposited using NH₃/SiH₄ flow rate ratios between 1 and 70 and substrate temperatures of 100 °C and 250 °C. For NH₃/SiH₄ ratios between 40 and 70, highly transparent (T ~ 90%), dense films (2.56-2.74 g/cm³) with good dielectric properties and refractive index between 1.93 and 2.08 were deposited on glass substrates. Etch rates in BHF of 2.7 ?/s and < 0.5 ?/s were obtained for films deposited at 100 °C and 250 °C, respectively. Films deposited at both substrate temperatures showed electrical conductivity ~ 10^− 14 Ω^− 1 cm^− 1 and breakdown fields > 10 MV cm^− 1.     

Ti2Al(O,N) formation by solid-state reaction between substoichiometric TiN thin films and Al2O3 (0001) substrates

Titanium nitride TiN_x (0.1 ≤ x ≤ 1) thin films were deposited onto Al₂O₃(0001) substrates using reactive magnetron sputtering at substrate temperatures (T_s) ranging from 800 to 1000 °C and N₂ partial pressures (pN₂) between 13.3 and 133 mPa. It is found that Al and O from the substrates diffuse into the substoichiometric TiN_x films during deposition. Solid-state reactions between the film and substrate result in the formation of Ti₂O and Ti₃Al domains at low N₂ partial pressures, while for increasing pN₂, the Ti₂AlN MAX phase nucleates and grows together with TiN_x. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) || Al₂O₃(0001) structure without the incorporation of substrate species. Growth at T_s 1000 °C yields Ti₂AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 °C, which contain also Ti₂AlN(101?3) grains. Finally, the Ti₂AlN domains incorporate O, likely on the N site, such that a MAX phase oxynitride Ti₂Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction and (scanning) transmission electron microscopy, together with spectroscopy methods, which comprise elastic recoil detection analysis, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy.     

Preparation of anatase TiO2 thin films by vacuum arc plasma evaporation

Anatase titanium dioxide (TiO₂) thin films with high photocatalytic activity have been prepared with deposition rates as high as 16 nm/min by a newly developed vacuum arc plasma evaporation (VAPE) method using sintered TiO₂ pellets as the source material. Highly transparent TiO₂ thin films prepared at substrate temperatures from room temperature to 400 °C exhibited photocatalytic activity, regardless whether oxygen (O₂) gas was introduced during the VAPE deposition. The highest photocatalytic activity and photo-induced hydrophilicity were obtained in anatase TiO₂ thin films prepared at 300 °C, which correlated to the best crystallinity of the films, as evidenced from X-ray diffraction. In addition, a transparent and conductive anatase TiO₂ thin film with a resistivity of 2.6 × 10^− 1 Ω cm was prepared at a substrate temperature of 400 °C without the introduction of O₂ gas.     

Effect of Cu dopant on microstructure and phase transformation of ZnTiO3 thin films prepared by radio frequency magnetron sputtering

Cu doped zinc titanate (ZnTiO₃) films were prepared using radio frequency magnetron sputtering. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that the as-deposited films were amorphous and contained 0.84 at.% Cu. This was further confirmed by the onset of crystallization that took place at annealing temperatures 600 °C. The phase transformation for the as-deposited films and annealed films was investigated in this study. The results showed that Zn₂Ti₃O₈, ZnTiO₃, and TiO₂ can coexist at 600 °C. When annealed at 700 °C, the results revealed that mainly the hexagonal ZnTiO₃ phase formed, accompanied by minority amounts of TiO₂ and Zn₂Ti₃O₈. Unlike pure zinc titanate films, this result showed that the Zn₂Ti₃O₈ phase can be stable at temperatures above 700 °C. Moreover, Cu addition in zinc titanate thin film could result in the decomposition of hexagonal (Zn,Cu) TiO₃ phase at 800 °C. When the Cu content was increased in zinc titanate thin films from 0.84 at.% to 2.12 at.%, there were only two phases; Zn₂Ti₃O₈ and ZnTiO₃, coexisting at temperatures between 700 and 800 °C. This result indicated that a greater presence of Cu dopants in zinc titanate thin films leads to the existence of the Zn₂Ti₃O₈ phase at higher temperatures.     

Phases in copper-gallium-metal-sulfide films (metal=titanium, iron, or tin)

The incorporation of metal impurities M (M = Ti, Fe, or Sn) into CuGaS₂ films is investigated experimentally as a function of impurity concentration. Films are synthesized by thermal co-evaporation of the elements onto glass/Mo substrates heated to 400 °C-570 °C. The compositions of the resulting films are measured by energy-dispersive X-ray spectroscopy and the structures of the present phases are studied by X-ray diffraction. The formation of Cu-M-S ternary phases is observed in a wide range of conditions. Films of Cu-Ga-Ti-S, synthesized at 500 °C, show the presence of a cubic modification of CuGaS₂ and Cu₄TiS₄. Alloying of CuGaS₂ and tetragonal Cu₂SnS₃ is observed for substrate temperatures of 450 °C. A miscibility gap opens at 500 °C and above with separate Sn-rich and Ga-rich phases. Similarly, alloys of CuFeS₂ and CuGaS₂ are only found in Cu-Ga-Fe-S films synthesized at lower substrate temperature (400 °C), whereas at 500 °C a miscibility gap opens leading to separate Fe-rich and Ga-rich phases.