Thermally stable, highly conductive, and transparent Ga-doped ZnO thin films

Highly conductive and transparent films of Ga-doped ZnO (GZO) have been prepared by pulsed laser deposition using a ZnO target with Ga₂O₃ dopant of 3 wt.% in content added. Films with resistivity as low as 3.3 × 10^− 4 Ω cm and transmittance above 80% at the wavelength between 400 and 800 nm can be produced on glass substrate at room temperature. It is shown that a stable resistivity for use in oxidation ambient at high temperature can be attained for the films. The electrical and optical properties, as well as the thermal stability of resistivity, of GZO films were comparable to those of undoped ZnO films.     

Growth of pseudocubic perovskite-type SrRuO3 thin films on quartz substrate using pulsed laser deposition method

Strontium ruthenium oxide (SrRuO₃) thin films have been grown using pulsed laser deposition technique on silicon, Pt coated silicon and quartz substrates. The effect of substrate temperatures on the structural, microstructure, and electrical properties of the SrRuO₃ films on quartz substrate has been investigated using XRD, SEM, AFM and four-probe method, respectively. The lowest resistivity at room temperature for the SrRuO₃ thin film on quartz substrate has been achieved at substrate temperature of 700 °C. Furthermore, the comparisons of SrRuO₃ thin films deposited on various substrates have been done with respect to structural, microstructural and electrical properties. XRD patterns exhibit that all thin films are a single phase, pseudo-cubic perovskite structure. Study of surface morphology shows that grain size and roughness varies with respect to substrate. It is observed that SrRuO₃ thin films yield larger grain size and root mean square roughness on Pt/Si substrate. Investigation of electrical properties shows that SrRuO₃ thin films can serve the purpose of the bottom electrode in dielectric and ferroelectric devices.     

Metalorganic chemical vapor deposition of SrRuO3 thin film and its characterization

Synthesis of conducting oxide strontium ruthenate is carried out in a hot-wall tubular reactor, using Sr(C₁₁H₁₉O₂)₂/Ru(C₅H₅)₂/O₂ reaction system. Owing to a large difference in depositing efficiency between strontium and ruthenium precursors, the stoichiometric ratio of thin film is controlled in one cycle of two consecutive depositions at different temperatures. Thin films of SrRuO₃ single phase are synthesized in the subsequent 700°C annealing. Thin films of SrRuO₃ with extra ruthenium oxide can also be prepared by adjusting the molar ratio of RuO₂ and SrO layers. The deposition sequence of ruthenium oxide first, strontium oxide later is preferred. If the deposition sequence is reverse, the thin film is plagued with unreacted oxides even when the annealing temperature is raised to 800°C. The relative ease of preparing SrRuO₃ thin films, when RuO₂ is under SrO, is attributed to evaporation of ruthenium oxide in O₂ and diffusion in its open columnar microstructure. The sheet resistivity of thin film decreases with the ruthenium content. The room temperature resistivity of SrRuO₃ film of Ru/(Sr + Ru) = 0.5 is around 910 ohm-cm. The room-temperature resistivity of Ru/(Ru + Sr) = 0.53 decreases to 470 ohm-cm. The root mean square surface roughness of 700°C synthesized SrRuO₃ thin film is 22 nm, in a 2 × 2 m² area of film thickness 280 nm.     

Structural, electrical and optical studies of SILAR deposited cadmium oxide thin films: Annealing effect

Successive ionic layer adsorption and reaction (SILAR) method has been successfully employed for the deposition of cadmium oxide (CdO) thin films. The films were annealed at 623 K for 2 h in an air and changes in the structural, electrical and optical properties were studied. From the X-ray diffraction patterns, it was found that after annealing, H₂O vapors from as-deposited Cd(O₂)_0.88(OH)_0.24 were removed and pure cubic cadmium oxide was obtained. The as-deposited film consists of nanocrystalline grains of average diameter about 20-30 nm with uniform coverage of the substrate surface, whereas for the annealed film randomly oriented morphology with slight increase in the crystallite size has been observed. The electrical resistivity showed the semiconducting nature with room temperature electrical resistivity decreased from 10⁻² to 10⁻³ Ω cm after annealing. The decrease in the band gap energy from 3.3 to 2.7 eV was observed after the annealing.     

Effect of high temperature annealing on the electrical performance of titanium/platinum thin films

In this study, the influence of post deposition annealing steps (PDA) on the electrical resistivity of evaporated titanium/platinum thin films on thermally oxidised silicon is investigated. Varying parameters are the impact of thermal loading with maximum temperatures up to T_PDA = 700 °C and the platinum top layer thickness ranging from 24 nm to 105 nm. The titanium based adhesive film thickness is fixed to 10 nm. Up to post deposition annealing temperatures of T_PDA = 450 °C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. Modifications in the intrinsic film stress strongly influence the electrical material parameter in this temperature regime. At T_PDA > 600 °C, diffusion of titanium into the platinum top layer and its plastic deformation dominate the electrical behaviour, both causing an increase in film resistivity above average.     

Growth of flat SrRuO3 (111) thin films suitable as bottom electrodes in heterostructures

Thin film growth of ferroelectric or multiferroic materials on SrTiO₃(111) with a buffer electrode has been hampered by the difficulty of growing flat electrodes on this polar orientation. We report on the growth and characterization of SrRuO₃ thin films deposited by pulsed laser deposition on SrTiO₃(111). We show that our SrRuO₃(111) films are epitaxial and display magnetic bulk-like properties. Films presenting a thickness between 20 and 30 nm are found to be very flat and therefore suitable as bottom electrodes in heterostructures.     

Thin film growth of epitaxial, polycrystalline and amorphous SrRuO3

The SrRuO₃ thin films were grown on amorphous fused silica and (100) single crystal LaAlO₃ substrates by pulsed laser deposition method. On fused silica substrates, polycrystalline SrRuO₃ thin film was obtained and below the crystallization temperature, SrRuO₃ thin films show an amorphous phase. For the case of epitaxial growth on (100) single crystal LaAlO₃ substrate, the crystallization temperature of SrRuO₃ thin film was increased by ∼ 100 °C indicating that additional energy is necessary in order to obtain the epitaxial thin film. By using the eclipse method and the control of substrate temperature, the variations of surface morphologies and grain size were observed by atomic force microscope. Below the crystallization temperature, amorphous SrRuO₃ thin film shows hopping transport property of an insulator.     

Characterization of ITO/CdO/glass thin films evaporated by electron beam technique

A thin buffer layer of cadmium oxide (CdO) was used to enhance the optical and electrical properties of indium tin oxide (ITO) films prepared by an electron-beam evaporation technique. The effects of the thickness and heat treatment of the CdO layer on the structural, optical and electrical properties of ITO films were carried out. It was found that the CdO layer with a thickness of 25 nm results in an optimum transmittance of 70% in the visible region and an optimum resistivity of 5.1×10⁻³ Ω cm at room temperature. The effect of heat treatment on the CdO buffer layer with a thickness of 25 nm was considered to improve the optoelectronic properties of the formed ITO films. With increasing annealing temperature, the crystallinity of ITO films seemed to improve, enhancing some physical properties, such as film transmittance and conductivity. ITO films deposited onto a CdO buffer layer heated at 450 °C showed a maximum transmittance of 91% in the visible and near-infrared regions of the spectrum associated with the highest optical energy gap of 3.61 eV and electrical resistivity of 4.45×10⁻⁴ Ω cm at room temperature. Other optical parameters, such as refractive index, extinction coefficient, dielectric constant, dispersion energy, single effective oscillator energy, packing density and free carrier concentration, were also studied.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Ru thin film grown on TaN by plasma enhanced atomic layer deposition

Ru thin films were sequentially deposited onto TaN (5 nm) by plasma enhanced atomic layer deposition using Ru(EtCp)₂ and NH₃ as precursors. The effect of growth temperature on the electrical resistivity and morphology of the Ru films were studied. It was found that the Ru films can achieve a low resistivity of 14 µΩ cm and a low root-mean-square roughness at a growth temperature of 270 °C. The thickness of the underlying TaN film was found to affect the Ru film growth. The oxidation of the very thin TaN film was correlated with the island growth of Ru. Ex and in-situ X-ray diffraction was employed to verify the copper diffusion barrier properties of a Ru (3 nm)/TaN (5 nm) bi-layer structure.     

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.     

Engineering of luminescence from Gd2O3:Eu nanophosphors by pulsed laser deposition

Nanostructured Gd₂O₃:Eu³⁺ thin films were prepared by pulsed laser ablation technique. The dependence of structural, morphological and optical properties of these films on photoluminescence was systematically studied by varying the annealing temperature, Eu³⁺ incorporation concentration and laser fluence. The intensity of the XRD peak from (2 2 2) crystal plane was found to increase with annealing temperature in the range 973–1173 K. Films annealed at 1173 K show a preferential growth along (2 2 2) crystal plane of the cubic Gd₂O₃ and enhanced photoluminescence at 612 nm. XRD and Micro-Raman spectra and lattice strain investigations suggest that Eu³⁺ incorporation introduce a strong lattice distortion in Gd₂O₃ matrix. Morphological investigations using atomic force microscopy indicate a strong influence of the annealing process on the surface roughness and particle size. This kind of transparent thin film phosphors may promise for applications in flat-panel displays and X-ray imaging systems.     

Characterization of ITO/CdO/glass thin films evaporated by electron beam technique

Abstract

A thin buffer layer of cadmium oxide (CdO) was used to enhance the optical and electrical properties of indium tin oxide (ITO) films prepared by an electron-beam evaporation technique. The effects of the thickness and heat treatment of the CdO layer on the structural, optical and electrical properties of ITO films were carried out. It was found that the CdO layer with a thickness of 25 nm results in an optimum transmittance of 70% in the visible region and an optimum resistivity of 5.1×10^?3 Ω cm at room temperature. The effect of heat treatment on the CdO buffer layer with a thickness of 25 nm was considered to improve the optoelectronic properties of the formed ITO films. With increasing annealing temperature, the crystallinity of ITO films seemed to improve, enhancing some physical properties, such as film transmittance and conductivity. ITO films deposited onto a CdO buffer layer heated at 450 °C showed a maximum transmittance of 91% in the visible and near-infrared regions of the spectrum associated with the highest optical energy gap of 3.61 eV and electrical resistivity of 4.45×10^?4 Ω cm at room temperature. Other optical parameters, such as refractive index, extinction coefficient, dielectric constant, dispersion energy, single effective oscillator energy, packing density and free carrier concentration, were also studied.     

Ferroelectric field effect in SrCuO2 and SrRuO3 films

We report on ferroelectric field effect experiments on Pb(Zr_0.52Ti_0.48)O₃/SrCuO₂ and Pb(Zr_0.52Ti_0.48)O₃/SrRuO₃ epitaxial heterostructures with an emphasis on the material characterization. Upon reversing the polarization of the Pb(Zr_0.52Ti_0.48)O₃ ferroelectric layer, we measured a nonvolatile change in the resistivity of ultrathin layers of SrCuO₂ and SrRuO₃. In thin SrRuO₃ films (30 Å) up to a 9% resistivity change has been observed at room temperature.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

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.     

Synthesis and electrochromic study of sol-gel cuprous oxide nanoparticles accumulated on silica thin film

In this study, electrochromic properties of cuprous oxide nanoparticles, self-accumulated on the surface of a sol-gel silica thin film, have been investigated by using UV-visible spectrophotometry in a lithium-based electrolyte cell. The cuprous oxide nanoparticles showed a reversible electrochromic process with a thin film transmission reduction of about 50% in a narrow wavelength range of 400-500 nm, as compared to the bleached state of the film. Using optical transmission measurement, we have found that the band gap energy of the films reduced from 2.7 eV for Cu₂O to 1.3 eV for CuO by increasing the annealing temperature from 220 to 300 °C in an N₂ environment for 1 h. Study of the band gaps of the as-deposited, colored and bleached states of the nanoparticles showed that the electrochromic process corresponded to a reversible red-ox conversion of Cu₂O to CuO on the film surface, in addition to the reversible red-ox reaction of the Cu₂O film. X-ray photoelectron spectroscopy indicated that the copper oxide nanoparticles accumulated on the film surface, after annealing the samples at 200 °C. Surface morphology of the films and particle size of the surface copper oxides have also been studied by atomic force microscopy analysis. The copper oxide nanoparticles with average size of about 100 nm increased the surface area ratio and surface roughness of the silica films from 2.2% and 0.8 nm to 51% and 21 nm, respectively.     

Investigation of thermal stability of Mo thin-films as the buffer layer and various Cu metallization as interconnection materials for thin film transistor-liquid crystal display applications

Cu/Mo/Si multi-layer structures were fabricated to investigate diffusion behaviors and thermal stability between Cu and Mo. Physical vapor deposition (PVD), chemical vapor deposition, electroplating and electrolessplating were used to grow 100 nm thick Cu films as interconnection materials, and radio-frequency sputtering system was introduced to grow 37.5 nm thick Mo films as a buffer layer. All Cu/Mo/Si multi-layer specimens were annealed at 350 to 700 °C for 30 min. When the annealing temperature was over 600 °C, the Cu diffused through Mo into Si, and the Cu₃Si phase and Mo-Si intermetallic compounds formed at the Mo/Si interface. The diffusion mechanism is the grain boundary diffusion. The results indicate that Cu film deposited by PVD had best crystallinity, lower roughness, large adhesive energy and resistivity. The values of the resistivity, diffusion activity energy and large adhesive energy are 5.47 μΩ-cm, 0.948 eV and 2.46 N/m, respectively.     

Study on TiO2 thin films grown by advanced pulsed laser deposition on ITO

TiO₂ films were grown by an advanced pulsed laser deposition method (PLD) on ITO substrates to be used as functional electrodes in the manufacturing of solar cells. A pure titanium target (99.99%) was irradiated by a Nd:YAG laser (355 and 532 nm, 5 ns, 35 mJ, 3 J/cm²) in an oxygen atmosphere at different pressures (20-160 mTorr) and at room temperature. After deposition, the films were subjected to an annealing process at 350 °C. The film structure, surface morphology, thickness, roughness, and optical transmission were investigated. Regardless of the wavelength used, the films deposited at room temperature presented only Ti₂O and TiO peaks. After thermal treatment, the TiO₂ films became strongly crystalline, with a tetragonal structure and in the anatase phase; the threshold temperature value was 250 °C. The deposition rate was in the range of 0.035-0.250 nm/pulse, and the roughness was 135-305 nm. Optical transmission of the films in the visible range was between 40% and 60%.     

Effects of thickness and post deposition annealing on the properties of evaporated In2S3 thin films

Indium sulfide (In₂S₃) films with three different thicknesses (150, 400 and 600 nm) were prepared using thermal evaporation at room temperature. As prepared samples were amorphous and subsequent annealing at higher temperature (>573 K) resulted in the formation of crystalline phase. Optical band gap was found in the range of 1.9–2.9 eV for as prepared samples and decreased with increase in annealing temperature. Interference fringe like structure in transmission spectra revealed that the films were fairly smooth and reflective. Variations in electrical resistivity and photosensitivity as a function of film thickness and annealing temperature were studied. X-ray Photoelectron Spectroscopic (XPS) studies clearly indicated uniform distribution of both indium and sulphur along the film. Energy Dispersive X-ray analysis showed that as prepared samples were stoichiometric.