Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Polypropylene filled with kaolinite-based conductive powders

Antimony doped tin oxide nanoparticles (Sb–SnO₂) were uniformly coated on the surfaces of rod-/flake-like kaolinites (Kaol) to synthesize kaolinite-based conductive powders (Sb–SnO₂)Kaol, which was then added into polypropylene (PP) matrix to produce conductive (Sb–SnO₂)Kaol–PP nanocomposites. The effects of (Sb–SnO₂)Kaol characteristics on the volume resistivity and mechanical properties of (Sb–SnO₂)Kaol–PP were in detail investigated. The results indicated that surface-modified (Sb–SnO₂)Kaol could improve the dispersion in PP matrix, and the as-synthesized nanocomposites showed better electrical property than that without surface modification. The volume resistivity of (Sb–SnO₂)Kaol–PP reached 7.3 × 10⁸ Ω·cm at the (Sb–SnO₂)Kaol concentration of 40%, 6–7 order of magnitude lower than that of pure PP. The as-synthesized (Sb–SnO₂)Kaol–PP nanocomposites could show potential applications in the conductive fields.     

Room temperature preparation of high performance AZO films by MF sputtering

Aluminum-doped zinc oxide (AZO) thin films have been deposited by MF magnetron sputtering from a ceramic oxide target without heating the substrates. This study has investigated effects of sputtering power on the structural, electrical and optical properties of the AZO films. The films delivered a hexagonal wurtzite structure with (002) preferential orientation and uniform surface morphology with 27–33 nm grain size. The results indicate that residual stress and grain size of the AZO films are dependent on sputtering power. The minimum resistivity of 7.56×10^?4 Ω cm combined with high transmittance of 83% were obtained at deposited power of 1600 W. The films delivered the advantages of a high deposition rate at low substrate temperature and should be suitable for the fabrication of low-cost transparent conductive oxide layer.     

Effects of annealing on wettability and physical properties of SnO thin films deposited at low RF power densities

The SnO thin films were deposited at low RF power densities by RF magnetron sputtering. According to XRD and XPS analyses, the SnO thin film comprised nanocrystalline orthorhombic SnO with a (110) orientation. Reducing RF power density resulted in better nanocrystallinity, changing hydrophobicity to hydrophilicity, and increasing the optical transmission in the UV–vis–NIR region. After annealing, the SnO thin film favored p-type conductivity and hydrophilicity. As the annealing temperature increased, the coexistence of nanocrystalline orthorhombic SnO and tetragonal SnO₂ in the film clearly increased the optical transmission in the ultraviolet region. The SnO thin films after annealing at 500 ℃ in vacuum and N₂ (200 sccm) exhibited a higher hole mobility and a better optical selection in the ultraviolet region, respectively.     

Structural,electrical and optical properties of molybdenum-doped TiO2 thin films

Molybdenum doped TiO₂ (MTO) thin films were prepared by radio frequency (RF) magnetron sputtering at room temperature and followed by a heat treatment in a reductive atmosphere containing 90% N₂ and 10% H₂. XRD and FESEM were employed to evaluate the microstructure of the MTO films, revealing that the addition of molybdenum enhances the crystallization and increases the grain size of TiO₂ films. The optimal electrical properties of the MTO films were obtained with 3 wt% Mo doping, producing a resistivity of 1.1×10^?3 Ω cm, a carrier density of 9.7×10²⁰ cm^?3 and a mobility of 5.9 cm²/Vs. The refractive index and extinction coefficient of MTO films were also measured as a function of film porosity. The optical band gap of the MTO films ranged from 3.28 to 3.36 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.14 eV was attributed to the Burstein–Moss effect.     

Growth and properties of Cu3SbS4 thin films prepared by a two-stage process for solar cell applications

Cu₃SbS₄ is a promising material for thin film heterojunction solar cells owing to its suitable optical and electrical properties. In this paper, we report the preparation of Cu₃SbS₄ thin films by annealing the Sb₂S₃/CuS stacks, produced by chemical bath deposition, in a graphite box held at different temperatures. The influence of annealing temperature on the growth and properties of these films is investigated. These films are systematically analyzed by evaluating their structural, microstructural, optical and electrical properties using suitable characterization techniques. X-ray diffraction analysis showed that these films exhibit tetragonal crystal structure with the lattice parameters a=0.537 nm and b=1.087 nm. Their crystallite size increases with increasing annealing temperature of the stacks. Raman spectroscopy analysis of these films exhibited modes at 132, 247, 273, 317, 344, 358 and 635 cm⁻¹ due to Cu₃SbS₄ phase. X-ray photoelectron spectroscopy analysis revealed that the films prepared by annealing the stack at 350 °C exhibit a Cu-poor and Sb-rich composition with +1, +5 and −2 oxidation states of Cu, Sb and S, respectively. Morphological studies showed an improvement in the grain size of the films on increasing the annealing temperature. The direct optical band gap of these films was in the range of 0.82–0.85 eV. Hall measurements showed that the films are p-type in nature and their electrical resistivity, hole mobility and hole concentration are in the ranges of 0.14–1.20 Ω-cm, 0.05–2.11 cm² V⁻¹ s⁻¹ and 9.4×10²⁰–1.4×10¹⁹ cm⁻³, respectively. These structural, morphological, optical and electrical properties suggest that Cu₃SbS₄ could be used as an absorber layer for bottom cell in multi-junction solar cells.     

Synthesis of high-quality AZO polycrystalline films via target bias radio frequency magnetron sputtering

The deposition rate, transmittance and resistivity of aluminium-doped zinc oxide (AZO) films deposited via radio frequency (r.f.) sputtering change with target thickness. An effective method to control and maintain AZO film properties was developed. The strategy only involved the regulation of target bias voltage of r.f. magnetron sputtering system. The target bias voltage considerably influenced AZO film resistivity. The resistivity of the as-deposited AZO film was 9.82×10⁻⁴ Ω cm with power density of 2.19 W/cm² at target self-bias of −72 V. However, it decreased to 5.98×10⁻⁴ Ω cm when the target bias voltage was increased to −112 V by applying d.c. voltage. Both growth rate and optical band gap of AZO film increased with the absolute value of target bias voltage – growth rate increased from 10.54 nm/min to 25.14 nm/min, and band gap increased from 3.57eV to 3.71 eV when target bias voltage increased from −72 V to −112 V at r.f. power density of 2.19 W/cm². The morphology of AZO films was slightly affected by the target bias voltage. Regulating target bias voltage is an effective method to obtain high-quality AZO thin films deposited via r.f. magnetron sputtering. It is also a good choice to maintain the quality of AZO film in uptime manufacturing deposition.     

Properties of solution-processed MgInZnO semiconductor thin films and photodetectors fabricated at a low temperature using UV-assisted thermal annealing

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10² Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I_light-to-I_dark ratio of 7.7 × 10² and had a photoresponsivity of 5.0 A/W at a bias of 5 V.     

Sputtering deposition of transparent conductive F-doped SnO2 (FTO) thin films in hydrogen-containing atmosphere

F-doped SnO₂ (FTO) thin films have been prepared by sputtering SnO₂-SnF₂ target in Ar+H₂ atmosphere. The effects of H₂/Ar flow ratio on the structural, electrical and optical properties of the films were investigated at two substrate temperatures of 150 and 300 °C and two base pressures of 3.5×10⁻³ and 1.5×10⁻² Pa. The results show that introducing H₂ into sputtering atmosphere can lead to the formation of a FTO film with a (101) preferred orientation and produce oxygen vacancy (V_O) at lower H₂/Ar flow ratios, but SnO phase at higher H₂/Ar flow ratios in the films. Accordingly, the resistivity of the films first decreases and then increases, but the transmittance decreases continuously with increasing H₂/Ar flow ratio. When H₂/Ar flow ratio is increased above a certain value, more amorphous SnO phase forms in the films, resulting in a big decrease in conductivity, transmittance, and band gap (E_g). Increasing substrate temperature can increase the Hall mobility due to the improvement of film crystallinity, but decrease the carrier concentration due to outward-diffusion of fluorine in the films. At a base pressure of 3.5×10⁻³ Pa, high substrate temperature (300 °C) can hinder the formation of SnO and thus improve the transparent conductive properties of the films. At a base pressure of 1.5×10⁻² Pa, the range of H₂/Ar flow ratio for forming the SnO₂ phase and hence for obtaining high transparent conductive FTO films is widened at both substrate temperatures of 150 and 300 °C.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Improving the electrical properties of niobium-doped titania sputtering targets by sintering in oxygen-deficient atmospheres

Niobium-doped titania (TNO) film can be used as a transparent conductive oxide (TCO) film due to its excellent conductivity and visible transparency. The performances of TNO sputtering targets are thus critical issues in optimizing sputtered films. This study clarifies the influences of inert and reducing atmospheres on the microstructure, densification, crystal structure, and electrical properties of TNO sputtering targets. The results indicate that a sintering atmosphere of 90% Ar–10% H₂ can result in a lower sintered density, larger grain size, and lower resistivity than can an atmosphere of Ar, followed by one of air. Sintering in 90% Ar–10% H₂ or Ar obviously decreases the resistivity of TiO₂, from >10⁸ Ω cm to <10⁻¹ Ω cm, and the TNO target, from >10¹ Ω cm to <10⁻¹ Ω cm. The resistivity of TNO target sintered at 1200 °C in 90% Ar–10% H₂ is as low as 1.8×10⁻² Ω cm.     

Low temperature processed SnO2 films using aqueous precursor solutions

We present a comparison study of the microstructure developments during aqueous solution deposition of SnO₂, particularly, through chemical bath deposition (CBD) and liquid phase deposition (LPD) at very low temperatures (40–75 °C). The effects of solution chemistry on the microstructural details and electrical properties of SnO₂ thin films are presented and discussed. Smooth, nanoparticulate SnO₂ films were obtained from supersaturated precursor solutions with lower precursor concentrations while more aggregated SnO₂ films were generated from higher precursor concentrations. Loosely-packed and porous structures were obtained from low supersaturation solutions with very low pHs. The deposition rates were also evaluated under various deposition conditions. XRD result shows that annealing process helps improve the degree of crystallinity of the as-deposited films that are composed of 3–10 nm nanocrystalline particles. One advantage of LPD of SnO₂ films is in-situ fluorine doping during deposition. The resulting electrical resistivity of F-doped SnO₂ films was about 18.7 Ω cm after the films were annealed at 450 °C.     

Preparation and characterization of transparent indium- doped TiO2 films deposited by MOCVD

Titanium dioxide (TiO₂) films doped with different indium (In) concentrations have been prepared on SrTiO₃ (STO) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) analyses revealed the TiO₂ films doped with low In concentrations to be [001] oriented anatase phase and the films with high In concentrations to present polycrystalline structures. The 1.8% In-doped TiO₂ film exhibited the best electrical conductivity properties with the lowest resistivity of 8.68×10⁻² Ω cm, a Hall mobility of 10.9 cm² V⁻¹ s⁻¹ and a carrier concentration of 6.5×10¹⁸ cm⁻³. The films showed excellent transparency with average transmittances of over 85% in the visible range.     

Electron trapping of laser-induced carriers in Er-doped SnO2 thin films

In order to investigate optically excited electronic transport in Er-doped SnO₂, thin films are excited with the fourth harmonic of an Nd:YAG laser (266 nm) at low temperature, yielding conductivity decay when the illumination is removed. Inspection of these electrical characteristics aims knowledge for electroluminescent devices operation. Based on a proposed model where trapping defects present thermally activated cross section, the capture barrier is evaluated as 140, 108, 100 and 148 meV for doped SnO₂ thin films with 0.0, 0.05, 0.10 and 4.0 at% of Er, respectively. The undoped film has vacancy levels as dominating, whereas for doped films, there are two distinct trapping centers: Er³⁺ substitutional at Sn⁴⁺ lattice sites and Er³⁺ located at grain boundary.     

Study of Cu-based Al-doped ZnO multilayer thin films with different annealing conditions

AZO/Cu/AZO multilayer thin films produced under different annealing conditions are studied in this paper, to examine the effects of atmosphere and annealing temperature on their optical and electrical properties. The multilayer thin films are prepared by simultaneous RF magnetron sputtering (for AZO) and DC magnetron sputtering (for Cu). The thin films were annealed in a vacuum or an atmosphere of oxygen at temperatures ranging from 100 to 400 °C in steps of 100 °C for 3 min. High-quality multilayer films (at Cu layer thickness of 15 nm) with resistivity of 1.99×10⁻⁵ Ω-cm and maximum optical transmittance of 76.23% were obtained at 400 °C annealing temperature in a vacuum. These results show the films to be good candidates for use as high quality electrodes in various displays applications.     

Fabrication of CaLa4(Zr0.05Ti0.95)4O15 thin films by RF magnetron sputtering

Crystalline CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films deposited on n-type Si substrates byRF magnetron sputtering at a fixed RF power of 100 W, an Ar/O₂ ratio of 100/0, an operating pressure of 3 mTorr, and different substrate temperatures were investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction and atomic force microscopy were sensitive to the deposition conditions, such as the substrate temperature. The diffraction pattern showed that the deposited films had a polycrystalline microstructure. As the substrate temperature increased, the quality of the CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films improved, and the kinetic energies of the sputtered atoms increased, resulting in a structural improvement of the deposited CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films. A high dielectric constant of 16.7 (f=1 MHz), a dissipation factor of 0.19 (f=1 MHz), and a low leakage current density of 3.18×10⁻⁷ A/cm² at an electrical field of 50 kV/cm were obtained for the prepared films.     

Structural and optoelectronic properties of transparent conductive c-axis-oriented ZnO based multilayer thin films with Ru interlayer

ZnO and Ru multilayer thin films are deposited using the sputtering deposition technique at room temperature. The effects of the Ru interlayer thickness and annealing temperature on the properties of multilayer thin films have been studied. An X-ray diffraction study reveals that ZnO layers are highly c-axis-oriented. The use of an Ru interlayer improves the crystalline quality of the subsequently deposited ZnO layers. Moreover, the crystalline quality of the entire structure is further enhanced through thermal annealing in a vacuum. Atomic force microscopy images show that the surface roughness of the multilayer thin films increases with a Ru interlayer thickness greater than 6 nm. The roughness of the film surface increases in correlation with annealing temperatures. This accounts for the decreased optical transmittance of the multilayer thin films annealed at temperatures higher than 450 °C. The electrical resistivity of multilayer thin films decreases with an increase in the metallic interlayer thickness. Thermal annealing at 450 °C causes low resistivity in multilayer thin films. The lowest resistivity reached ～5.4 × 10^?4 Ω cm for multilayer films with a 10-nm-thick Ru interlayer annealed at 450 °C.     

Characterization of Cu(In,Ga)Se2 thin films prepared by RF magnetron sputtering using a single target without selenization

Cu(In_1?xGa_x)Se₂ (CIGS) thin films were prepared using a single quaternary target by RF magnetron sputtering. The effects of deposition parameters on the structural, compositional and electrical properties of the films were examined in order to develop the deposition process without post-deposition selenization. From X-ray diffraction analysis, as the substrate temperature and Ar pressure increased and RF power decreased, the crystallinity of the films improved. The scanning electron microscopy revealed that the grains became uniform and circular shape with columnar structure with increasing the substrate temperature and Ar pressure, and decreasing the RF power. The carrier concentration of CIGS films deposited at the substrate temperature of 500 °C was 2.1 × 10¹⁷ cm^?3 and the resistivity was 27 Ω cm. At the substrate temperature above 500 °C, In and Se contents in CIGS films decreased due to the evaporation and it led to the deterioration of crystallinity. It was confirmed that CIGS thin films deposited at optimal condition had similar atomic ratio to the target value even without post-deposition selenization process.     

Synthesis and characterization of Sb–SnO2/kaolinites nanoparticles

In this paper, we reported the synthesis of composite conductive powders of antimony-doped tin oxide (Sb–SnO₂) coated onto kaolinite. Structure and morphology of the samples were systematically characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that Sb–SnO₂ nanoparticles (< 10 nm) were successfully coated as thin layers on the surface of kaolinite. The antimony-doped tin oxide/kaolinite (ATK) composites retained the flake morphology like the original kaolinite and had a resistivity of 273.2 Ω·cm. Sb–SnO₂ layers were proved to attach to the kaolinite surface via the Sn–O–Si or Sn–O–Al bonds. The growth mode of Sb–SnO₂ layers onto the kaolinite was investigated.     

Dielectric properties and bright red emission of Y3+/Eu3+-codoped ZrO2 thin films prepared by chemical solution deposition

We report on an effective combination of good dielectric properties with bright red emission in Y³⁺/Eu³⁺-codoped ZrO₂ thin films. The thin films were deposited on fused silica and Pt/TiO₂/SiO₂/Si substrates using a chemical solution deposition method. The crystal structure, surface morphology, electrical and optical properties of the thin films were investigated in terms of annealing temperature, and Y³⁺/Eu³⁺ doping content. The 5%Eu₂O₃–3%Y₂O₃–92%ZrO₂ thin film with 400 nm thickness annealed at 700 °C exhibits optimal photoluminescent properties and excellent electrical properties. Under excitation by 396 nm light, the thin film on fused silica substrate shows bright red emission bands centered at 593 nm and 609 nm, which can be attributed to the transitions of Eu³⁺ ions. Dielectric constant and dissipation factor of the thin films at 1 kHz are 30 and 0.01, respectively, and the capacitance density is about 65.5 nf/cm² when the bias electric field is less than 500 kV/cm. The thin films also exhibit a low leakage current density and a high optical transmittance with a large band gap.