Transparent amorphous Indium-Gallium-Zinc-Oxygen thin film transistors using solution technology at low temperature

Transparent amorphous Indium-Gallium-Zinc-oxide thin films transistors (a-IGZO TFTs) were fabricated using spin-coating technique at a relative low annealing temperature of 300 °C. The effects of the gallium (Ga) concentration on the properties of the IGZO solutions, the optical properties of the a-IGZO films,and the a-IGZO TFTs device properties were researched. The a-IGZO thin films were uniform and smooth, root mean square roughness of IGZO films was less than 0.4 nm, and the transmittance was more than 80 % in the visible wavelength. The results showed that An appropriate amount of Ga doping and annealing temperature could significant improve the a-IGZO TFTs’ device performance. A saturation mobility of 0.04 cm² V^?1 s^?1 was obtained when the Ga concentration reached 10.7 %.     

Improvement of electrical properties of sol–gel derived ZnO:Ga films by infrared heating method

In this study, we investigated the influences of gallium concentration and a rapid thermal annealing process on the electrical and optical properties of ZnO:Ga (GZO) films prepared by sol–gel method. Experimental data indicated that the preferential growth directions of ZnO crystallites were the (002) and (103) axes. This phenomenon implied that the nucleation and growth behaviors of ZnO crystallites were changed by the infrared heating procedure and monoethanolamine. Furthermore, since the deposited sol films were heated simultaneously, evenly, and rapidly, dopant material Ga got the opportunity to replace Zn instead of forming oxides embedded in grain boundary areas. Thus, carrier concentration of the GZO films can be considerably enhanced while the mobility of the GZO films was not apparently affected in our experiments. It was also found that the carrier concentration was not sensitive to Ga/Zn ratio even though higher Ga concentration led to lower mobility. The best sample with a resistivity of 2.20 × 10⁻³ Ω cm and a transmittance of over 80% in visible region was achieved with 1.0 at.% Ga.     

Enhancement of optical conductivity in the ultra-violet region of Cs doped ZnO sol gel thin films

Nano crystalline cesium (Cs) doped ZnO thin films were deposited on glass substrate by sol gel spin coating method with 1–3 mol.% doping concentration and different annealing temperatures. The deposited films were characterized by X-ray diffraction (XRD), Hall Effect, Photoluminescence (PL) and UV–Visible studies. XRD measurements reveal that all the samples abound in the wurtzite structure with polycrystalline nature. An increase in crystalline size from 19.60 to 44.54 nm is observed with the increase of doping concentration. Electrical conductivity of Cs doped ZnO films were observed from Hall effect measurements and the maximum carrier concentration obtained is 7.35 × 10¹⁸ cm^?3. The near band emission (384 nm) peak intensity increases with the increase of Cs doping concentration and a maximum intensity 55,280 was observed for CZ3 film from PL spectrum. Also a low energy near infrared (NIR) emission peak centered at 1.62 eV appears for the Cs doped ZnO films. The average transmission of CZ film is 88 % and the absorption edge is red shifted with the increase of Cs doping concentration and also the optical conductivity increases in the UV region.     

Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

Optical,electrical, and electrochemical behavior of p-type nanostructured SnO<Subscript>2</Subscript>:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO₂ thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO₂ thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO₂ sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO₂ thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni²⁺ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm² (V s)^?1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO₂ thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2?×?10^?15 to 6.5?×?10^?15 cm² s^?1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.     

Investigation of photocatalytic and low-emissivity properties of TiO2:F films featuring columnar structure prepared on SnO2:F substrate by sol–gel method

Fluorine-doped TiO₂ thin films featuring columnar structure were prepared on fluorine-doped tin oxide (SnO₂:F) substrate using a sol–gel method. The F doping ratios were varied in the range of 0–8 %. The effect of [F]/[Ti + F] ratio on the structural, morphological, optical, photocatalytic and low-emissivity properties has been investigated in detail. X-ray diffraction studies revealed that all the composited films are mainly composed of anatase TiO₂ and rutile SnO₂ without other phases. The prepared TiO₂:F films possessed the columnar morphology with the single layer thickness ranging from 28 to 31 nm. The best photocatalytic activity was obtained for the films with 4 % F doping ratio which is mainly attributed to the highest crystallization and crystallite size. The transmission and hemispherical emissivity of the composite films could still reach approximately 70 % and 0.20, which match the requirements of the Chinese National Standard (GB/T18915.2-2002), promoting the films for the practical applications.     

Sol–gel processed indium zinc oxide thin film and transparent thin-film transistors

Indium–zinc oxide (IZO) thin films were fabricated by spin coating using acetate- and nitrate-based precursors, and thin film transistors (TFTs) were further fabricated employing the IZO films as the active channel layer. The impact of the indium concentration on the properties of the solutions, the structure and optical transmittance properties of the IZO films and the IZO TFTs device properties were researched in this article. The IZO films with amorphous structure were obtained when the annealing temperature is 500 °C. The transmittance could reach ~90 % (including glass substrate) during the visible region of 400–760 nm. Higher indium concentration can improve the IZO TFTs’ filed effect mobility. A I_on–I_off of 6.0 × 10⁶ and a mobility of 0.13 cm²/Vs were obtained when the indium concentration is 60 %. IZO TFTs’ performance could deteriorate when the indium concentration more than 60 %.     

Effect of silica surface coating on the luminescence lifetime and upconversion temperature sensing properties of semiconductor zinc oxide doped with gallium(III) and sensitized with rare earth ions Yb(III) and Tm(III)

Optical sensing of temperature by measurement of the ratio of the intensities of the 700 nm emission and the 800 nm emission of Ga(III)-doped ZnO (GZO) nanoparticles (NPs) and of GZO NPs coated with a silica shell are demonstrated at 980 nm excitation. It is found that the relative sensitivity of SiO₂@Yb/Tm/GZO is 6.2% K^?1 at a temperature of 693 K. This is ~3.4 times higher than that of Yb/Tm/GZO NPs. Obviously, the SiO₂ shell structure decreases the rate of the nonradiative decay. The decay time of the 800 nm emission of the Yb/Tm/GZO NPs (15 mol% Ga; 7 mol% Yb; 0.5 mol% Tm) displays a biexponential decay with a dominant decay time of 148 μs and a second decay time of ~412 μs. The lifetime of the Yb/Tm/GZO NPs at 293 K, and of the SiO₂@Yb/Tm/GZO NPs are ~412 μs. Both the Yb/Tm/GZO and SiO₂@Yb/Tm/GZO can be used up to 693 K. These results indicate that the SiO₂ shell on the Yb/Tm/GZO is beneficial in terms of sensitivity and resolution.

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Graphical abstract The enhancement the decay time and thermal sensitivity in the SiO₂@Yb/Tm/GZO shell@core structure have been studied compared to the Ga(III)-doped Yb/Tm-doped ZnO (Yb/Tm/GZO). The SiO₂@Yb/Tm/GZO have good thermal accuracy up to 693 °C.

     

Structural modification and band gap tailoring of zinc oxide thin films using copper impurities

The doping effects of Cu on structural, morphological and optical properties of ZnO thin films and their PEC properties have been investigated via chemical bath deposition (CBD) technique at 353 K bath temperature and a pH of 11.5 with post-deposition annealing at 673 K. The concentration of Cu in ZnO varied between 1 and 5 at.%. X-ray diffraction analysis revealed that the synthesized Cu-doped ZnO (CZO) thin films were highly crystalline with hexagonal wurtzite structure, showing strong preferential growth along the c-axis for 3 at.% Cu concentration. A shift in angular peak position of 0.545^o in 2θ towards higher angle was observed for CZO films which is an indication of effective substitution of Cu atoms on Zn lattice. Crystallite sizes were enhanced from 28 to 32 nm in the (002) crystal plane. Optical analysis indicates a red shift in the absorption band edge up to 450 nm upon Cu doping. Transmittance characteristics increased slightly from 80 to 90% in the visible range at optimum Cu concentration of 3 at.%. Optical energy band gap was found to decrease from 3.03 eV for undoped ZnO to 2.7 eV upon Cu doping. The morphological structures of the CZO thin films were strongly influenced by Cu impurities and its concentration. The water contact angles showed strong dependence on Cu impurities in ZnO and decreased considerably from 71.3 to 15.2°. The synthesized CZO films showed enhanced photoelectrochemical properties, giving a short circuit current (I _sc) of 0.098 mAcm^?2 and open circuit voltage (V _oc) of 796 mV for an optimum Cu concentration of 3 at.% with photoconversion efficiency of 0.062% and fill factor of 63%.

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Graphical abstract

     

Synthesis,characterization, and optical studies of pentoxy-substituted tetrakis(pentafluorobenzyloxy)phthalocyanines

Abstract

The synthesis and characterization of peripherally 2′,3′,5′,6′-tetrafluoro-4′-pentoxy-benzyloxy-substituted metal-free and metallo (Zn(II) and Co(II)) phthalocyanines are described in this study. Aggregation properties of these phthalocyanines were studied in the concentration range of 1 × 10^?5?1 × 10^?6 M in tetrahydrofuran. Thin films of phthalocyanines were prepared by spin-coating technique. The spectrophotometric measurements of transmittance spectra were carried out in the wavelength range of 200–1000 nm. Optical band gaps of phthalocyanine thin films were also calculated. Surface morphologies and thickness of the films were examined by Scanning Electron Microscopy. Results show that film thickness can be changed significantly depending on the type of metal in the phthalocyanine.     

Structural,electrical and optical properties of tin doped cadmium oxide thin films obtained by sol–gel

Transparent and conducting tin doped cadmium oxide thin films were obtained by mixing cadmium oxide and tin oxide precursor solutions by the sol–gel method. Different tin contents in solution were studied: 0, 0.5, 1, 2, 3, 5 and 10 at.%. The films were sintered at 550 °C and, after that, annealed in N₂/H₂ gas mixture, in order to decrease their resistivity. X-ray diffraction patterns showed that doping of tin diminishes the [111] light preferred orientation of films and provokes a decrease of the average crystallite size from 30 to 12 nm. Atomic force microscopy images revealed morphological changes with the addition of tin content. All the films showed a high transmission around 75 % in the 600 < λ < 1,700 nm range and a shift of the absorption edge towards the blue region as the tin concentration was increased. The cadmium oxide films doped with 1 at.% of tin showed the lowest resistivity of 5.7 × 10^?4 Ω cm and a band gap energy value of 2.7 eV. For their characteristics, these CdO:Sn films are good candidates as transparent conductive electrodes in CdS/CdTe and CdS/CIGS type solar cells.     

Effect of lithium doping on the photoluminescence of Sm:ZnO powders

ZnO co-doped with 2 at.% Sm and different Li concentration (0–7 at.%) powders were fabricated by the sol–gel method with 700 °C annealing. The effect of Li doping concentration on the structure and photoluminescence (PL) of ZnO powders doped with 2 at.% Sm was investigated. Based on the balance of structure and valence, with the help of Li doping (1, 2 at.%) into ZnO powders doped with 2 at.% Sm, Sm³⁺ ions enter ZnO crystal lattice and induce the characteristic Sm³⁺ emission peaks by the ultra-violet (UV) excitation (278 nm). Especially, when the Li doping concentration is 2 at.%, the sample has the most efficient Sm characteristic emission line. However, Li will hinder the substitution of zinc location by Sm³⁺ when the Li doping concentration is above 3 at.%, which results in the disappearance of the characteristic samarium emission lines.     

Effects of growth behaviors on chemical and physical properties of sol–gel derived ZnO:Ga films

In this study, we investigated the effects of different heating processes on the structural, electrical and chemical properties of ZnO:Ga (GZO) films from the viewpoint of nucleation and growth behaviors. An infrared heating furnace and a traditional tube furnace were employed for the homogeneous and heterogeneous nucleation of GZO films. XRD patterns demonstrated that the preferential growth orientation of both kinds of GZO films is still the (002) direction. XPS data implied that the infrared heating process enables more uniform distribution of the dopant material and retards the oxidization of gallium in grain boundary areas. At the same time, the textured crystallite might provide a free tunnel for oxygen diffusion. Thus, the activation of free charge carriers could be more efficient when the GZO films were annealed under vacuum. As a result, the samples annealed by the infrared heating furnace had a noticeably high carrier concentration. Although the mobility was slightly smaller than that of the samples annealed by the tube furnace, film resistivity dropped obviously in general.     

Microstructure and optical properties of Ag-doped ZrO2 thin films prepared by sol gel method

Ag doped ZrO₂ thin films were deposited on quartz substrates by sol–gel dip coating technique. The effect of Ag doping on tetragonal to monoclinic phase transformation of ZrO₂ at a lower temperature (500 °C) was investigated by X-ray diffraction. It is found that the Ag doping promotes the phase transformation. The phase transformation can be attributed to the increase in the tetragonal grain size and concentration of oxygen vacancies in the presence of the Ag dopant. Accumulation of the Ag atoms at the film surface and surface morphology changes in the films were observed by AFM as a function of varying Ag concentration. X-ray photoelectron spectroscopy gave Ag 3d and O 1s spectra on Ag doped thin film. The chemical states of Ag have been identified as the monovalent state of Ag⁺ ions in ZrO₂. The Ag doped ZrO₂ thin films demonstrated the tailoring of band gap values. It is also found that the intensity of room temperature photoluminescence spectra is suppressed with Ag doping.     

Simultaneous Determination of Gallium(III) and Indium(III) in Urine and Water Samples with Cloud Point Extraction and by Inductively Coupled Plasma Optical Emission Spectrometry

A simple, sensitive, and selective method for the determination of gallium and indium in different samples at trace levels is presented. This method was based on complexation of analyzes with 2-(5-bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in the presence of t-octylphenoxy-polyethoxyethanol (Triton X-100). After phase separation, the analyzed concentrations were determined by inductively coupled plasma optical emission spectrometry. Quantitative extraction of gallium and indium was performed at pH 7.0, 1.7 mmol L^?1, 5-Br-PADAP, 1.3% (w/v) Triton X-100 and at 75°C. The relative standard deviations (RSD) of this method were between 0.3% and 1.6% (C = 20 ng mL^?1, n = 9). The calibration curve is linear over the concentration range 6–200 ng mL^?1 for gallium and 2–200 ng mL^?1 for indium, respectively. The limits of detection (LOD) for gallium and indium were 0.72 and 0.28 ng mL^?1, respectively. The results showed the developed method was not susceptible to matrix effects, providing recoveries between 98% and 102%. The accuracy of the developed method was evaluated by the analysis of spiked certified reference materials. The developed method was successfully applied to gallium and indium determination in urine and lake water with satisfactory results.     

Preparation and nonlinear optical properties of Au nanoparticles doped TiO2 thin films

Nano-sized noble metal nanoparticles doped dielectric composite films with large third-order nonlinear susceptibility due to the confinement and the enhancement of local field were considered to be applied for optical information processing devices, such as optical switch or all optical logical gates. In this paper, sol–gel titania thin films doped with gold nanoparticles (AuNPs, ~10 nm in average size) were prepared. AuNPs were firstly synthesized from HAuCl₄ in aqueous solution at ~60 °C, using trisodium citrate as the reducing agent, polyvinylpyrrolidone as the stable agent; then the particle size and optical absorption spectra of the AuNPs in aqueous solutions were characterized by transmitting electron microscopy and UV–Vis–NIR spectrometry. Sol–gel 2AuNPs–100TiO₂ (in %mol) thin films (5 layers, ~1 μm in thickness) were deposited on silica glass slides by multilayer dip-coating. After heat-treated at 300–1,000 °C in air, the AuNPs–TiO₂ thin films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The nonlinear optical properties of the AuNPs–TiO₂ thin films were measured with the Z-scan technique, using a femtosecond laser (200 fs) at the wavelength of 800 nm. The third-order nonlinear refractive index and nonlinear absorption coefficient of 2AuNPs–100TiO₂ films were at the order of 10^?12 cm²/W, and the order of 10^?6 cm/W, respectively, and the third-order optical nonlinear susceptibility χ⁽³⁾ was ~6.88 × 10^?10 esu.     

Synthesis of Cu2ZnSnS4 thin films by dip-coating method without sulphurization

Quaternary Cu₂ZnSnS₄ (CZTS) thin films, a promising absorber material for solar cells has been successfully deposited on glass substrates by cost effective simple dip-coating method without using either polluting chemicals or expensive vacuum facilities. X-ray diffraction pattern reveals the formation of CZTS films with tetragonal type kesterite structure. The Raman spectra of the prepared films exhibited resonance peaks corresponding to the CZTS phase. The scanning electron microscopic image shows the formation of films with smooth surface. The surface topography studied using atomic force microscope gives an rms roughness of 1.6 nm. The Hall effect studies indicate that the prepared films are p-type with a carrier concentration of 4.77 × 10²⁰ cm^?3. The energy dispersive X-ray analysis result indicate the presence of Cu, Zn, Sn and S in the film. The absorption coefficient was found to be the order of 10⁴ cm^?1 and the band gap has been found to be 1.5 eV.     

Wetting films on a hydrophilic silica surface obtained from aqueous solutions of hydrophobically modified inulin polymeric surfactant

The thickness of wetting films on a hydrophilic silica surface was investigated using a microinterferometric technique. Aqueous solutions of hydrophobically modified inulin (INUTEC^®SP1) at various concentrations, in the presence or absence of NaCl or Na₂SO₄, were studied. The equilibrium film thickness (h _eq) showed a complex dependence on INUTEC^®SP1 concentration. At low electrolyte concentrations, h _eq decreased with an increase in INUTEC^®SP1 concentration, reaching a minimum at 10^?6 mol dm^?3. However, at high electrolyte concentrations, this dependence became less pronounced. At any given INUTEC^®SP1 concentration, the equilibrium film thickness decreased with an increase in electrolyte concentration as a result of the compression of the electrical double layer reaching a minimum value. After that, the film thickness showed a small decrease with further increase in electrolyte concentration. This indicates that the electrostatic component of disjoining pressure can be neglected, and the steric repulsion of the loops and tails of INUTEC^®SP1 determined the film thickness.     

Structural improvement of ZnO electrodes through solution-processed routes for enhancing open-circuit voltage in dye-sensitized solar cells

We report herein one of our recent studies on nanostructured ZnO electrodes for application in dye-sensitized solar cells, focusing on achieving a higher open-circuit voltage (V_OC). ZnO films were obtained through solution-processed routes including pyrolytic conversion of layered hydroxide zinc acetate (LHZA) films deposited on a fluorine-doped tin oxide-coated conducting glass substrate by a chemical bath deposition method. The morphology of the initial LHZA and the converted ZnO films was tuned from a thick (approximately 12 μm) flower bed-/lawn-like bilayer structure to a thin (1.2 μm) lawn-like quasi-monolayer structure by decreasing the Zn source concentration in the chemical bath. V_OC was found to be enhanced with this morphological change from 0.692 (the bilayer structure) to 0.735 V (the quasi-monolayer structure). Fine tuning of the quasi-monolayer structure by introducing the grain growth effect led to V_OC of the cell as high as 0.807 V, although a short-circuit photocurrent density (J_SC) remained low. Further attempts were then made to increase J_SC while maintaining the high V_OC. When the thickness of the lawn-like monolayer film was increased up to approximately 5 μm, the resultant cell showed V_OC?=?0.750 V, J_SC?=?6.20 mA cm^?2 and a conversion efficiency (η) of 2.83%. The film with a modified flower bed-/lawn-like bilayer structure approximately 11 μm in thickness finally yielded V_OC?=?0.741 V, J_SC?=?13.6 mA cm^?2, and η?=?5.44%.     

Enhanced ferroelectric,dielectric and leakage properties in Ce and Ti co-doping BiFeO3 thin films

Pure BiFeO₃ (BFO), Ce and Ti individual doping and co-doping BiFeO₃ thin films were fabricated via sol–gel process on Pt/Ti/SiO₂/Si substrates. The microstructure, surface morphology, ferroelectric and dielectric properties of BFO and doped thin films were investigated in detail. X-ray diffraction reveal that all thin films are confirmed the formation of the distorted rhombohedral perovskite structure. No impure phase is identified in all the films. The Ce and Ti co-doping BiFeO₃ (BCFTO) thin films exhibited the enhanced ferroelectricity with a large remnant polarization (2P _r) of 130 μC/cm², and low leakage current density of 9.10 × 10^?6 A/cm² which is more than two orders of magnitude lower than that of pure BFO films at 100 kV/cm. The dielectric constant (364 at 1 kHz) of the BCFTO thin films is much larger than that of pure BFO thin films. These results suggest that the introductions of Ce and Ti provides an effective route for improving the ferroelectric, dielectric and leakage properties of BFO thin films.