Indium-doped Zinc Oxide Films Research Articles

Study of Atmospheric-Pressure Plasma Enhanced Chemical Vapor Deposition Fabricated Indium Gallium Zinc Oxide Thin Film Transistors with In-Situ Hydrogen Plasma Treatment.

Amorphous InGaZnO (a-IGZO) Thin Film Transistors (TFTs) has been studied extensively for their perspective applications in next generation active-matrix displays such as liquid crystal displays and flat-panel displays, due to its better field-effect mobility (>10 cm²/V · S), larger Ion/Ioff ratio (>106), and better stability electrical. Hydrogen is known as shallow donors for n-type (channel) oxide semiconductors (Dong, J.J., et al. 2010. Effects of hydrogen plasma treatment on the electrical and optical properties of Zno films: Identification of hydrogen donors in ZnO. ACS Appl. Mater. Interfaces, 2, pp.1780-1784), and it is also effective passivator for traps (Tsao, S.W., et al., 2010. Hydrogen-induced improvements in electrical characteristics of a-IGZO thin-film transistors. Solid-State Electron, 54, pp.1497-1499). In this study, In-Situ hydrogen plasma is applied to deposit IGZO channel. With atmospheric-pressure PECVD (AP-PECVD), IGZO thin film can be deposited without vacuum system, large area manufacturing, and cost reducing (Chang, K.M., et al., 2011. Transparent conductive indium-doped zinc oxide films prepared by atmospheric pressure plasma jet. Thin Solid Films, 519, pp.5114-5117). The results show that with appropriate flow ratio of Ar/H₂ plasma treatment, the a-IGZO TFT device exhibits better performance with mobility (μFE) 19.7 cm²/V · S, threshold voltage (VT) 1.18 V, subthreshold swing (SS) 81 mV/decade, and Ion/Ioff ratio 5.35×107.

Physical properties of indium zinc oxide and aluminium zinc oxide thin films deposited by radio-frequency magnetron sputtering

Indium-doped zinc oxide (IZO) and aluminium-doped zinc oxide (AZO) thin films were grown by radio-frequency (RF) magnetron sputtering onto optical glass substrates and their structural, morphological, and optical properties were discussed in terms of varying the sputtering power as 40 W, 60 W, 80 W, and 100 W. No heating substrate or any post-thermal treatment was performed. The structural features were analyzed by grazing incidence X-ray diffraction and revealed the amorphous phase for IZO samples, while the AZO thin films inherited the Wurtzite structure of zinc oxide. The morphological properties were investigated by atomic force microscopy (AFM), in tapping mode and scanning electron microscopy (SEM). The AFM images showed relatively uniform and smooth surfaces for all prepared structures. The optical transmission spectra proved the excellent theoretical values of transparency for metallic oxides in the visible region of the electromagnetic spectrum, i.e. ∼60% for IZO and ∼70% for AZO. The obtained results showed that even without any thermal treatment the structural, morphological, and optical properties of IZO and AZO thin films prepared by RF magnetron sputtering are similar with those for samples subjected to medium or high temperatures.

Enhanced luminescence property of 1 D nanorods realised by aqueous chemical growth on indium doped zinc oxide thin films

The current piece of research aims at the depiction of the adaptability of the 1 D nanorods on Zinc Oxide (ZnO) for Light Emitting Diode applications. Undoped and Indium doped ZnO films are deposited on glass substrates by Spray Pyrolysis at 425 °C. The indium doping level is varied from 1 to 4 at. % and the variation of structural, morphological and opto - electronic properties with indium doping are studied. The films with 2.5 at. % of indium doping showed better transmittance (~90%) and low electrical resistivity (1.77 × 10−2 Ωcm). 1 D nanorods have been deposited on In:ZnO thin films with better luminescence properties by Aqueous Chemical Growth (ACG) technique at various time durations. It is found that the morphology of the seed layer is the major factor determining the alignment of the nanorods. The In:ZnO 1 D nanorods deposited at 10 hours of ACG process is seen to have better electrical conductivity due to the effective networking of the nanorods. The X-Ray Diffraction analysis and X-Ray Photoelectron Spectroscopy analysis confirms the effective indium incorporation in the nanorods. The photoluminescence emission is found to depend strongly on the duration of ACG process and various defects are assigned for the emission in the visible region.

Rapid Processing of In-Doped ZnO by Spray Pyrolysis from Environment-Friendly Precursor Solutions

This study focused on the deposition of indium-doped zinc oxide (IZO) films at high growth rates by ultrasonic spray pyrolysis. We investigated the influence of processing parameters, such as temperature and solution flow rate, on the structural, optical, and electrical film properties. For all depositions, low-cost and low-toxicity aqueous solutions and metal salt precursors were used. Through the optimization of the spraying parameters and pattern, a spatially homogeneous IZO layer with transparency greater than 80%, resistivity of 3.82 × 10−3 Ω·cm for a thickness of 1800 nm (sheet resistance of 21.2 Ω/sq), Hall carrier density of 1.36 × 1020 cm−3, Hall mobility of 12.01 cm2 V−1 s−1, and work function of 4.4 eV was obtained. These films are suitable for implementation in optoelectronic and photovoltaic devices.

Fractal and multifractal analysis of In-doped ZnO thin films deposited on glass, ITO, and silicon substrates

Indium-doped zinc oxide (IZO) thin films have been deposited on glass (IZO/glass), ITO (IZO/ITO), and silicon (IZO/Si) substrates using sol–gel spin coating method. Glancing angle X-ray diffraction has been used to verify phase purity, average grain size, and microcrystalline stress of the annealed films. Effect of substrates on surface morphology is explicitly investigated using the conventional statistical techniques along with nonlinear fractal and multifractal geometrical analysis. The root-mean-square surface roughness value is the lowest in IZO/glass films and increases in IZO/ITO films and the highest in IZO/Si films. Fractal and multifractal formalism acts as a scale-independent microscopic analytical tool for surface analysis. All IZO films show fractal and multifractal behaviour. The fractal parameters such as fractal dimensions and Hurst exponents are different for films deposited on different substrates and, thus, able to characterize surface morphology precisely. Hurst exponent values of IZO films indicate that although IZO/Si films have highest vertical roughness, it has strongly correlated (highest self-similarity) surface morphology than other two films deposited on glass and ITO substrates. Inhomogeneity in scaling exponents could be better understood with the help of multifractal formalism. The difference of fractal dimensions in all IZO films deposited on glass, ITO, and Si substrates is very small (almost close to zero). Therefore, there is very little multifractality exist in those film surfaces. Width of multifractal spectrum is the largest in IZO/Si and the smallest (also similar) in IZO/ITO and IZO/glass films, indicating that multifractallity in IZO/Si film is more prominent. A quantitative information about the surface morphology has been provided by inferring multifractal parameters. Detailed fractal and multifractal formalism of surface morphology may find its importance in understanding various surface-based device fabrication and performances.

Ion-beam-induced surface modification of solution-derived indium-doped zinc oxide film for a liquid crystal device with stable and fast switching properties

The characteristics of a solution-derived indium-doped zinc oxide (In:ZnO) film exposed to ion-beam (IB) irradiation as a liquid crystal (LC) alignment layer were investigated. Solution processing was conducted to deposit a thin layer on a substrate and irradiation at various IB irradiation energies was used as an LC alignment method, all of which achieved uniform and homogeneous LC alignment. Atomic force microscopy using three-dimensional imaging and numerical analyses showed that the IB irradiation reduced the surface roughness. Through the X-ray photoelectron spectroscopy, it was revealed that the modification of the chemical composition due to the IB irradiation affected the state of the LC alignment. Increased polarizability of the surface and oxygen vacancies induced strong van der Waals forces between the In:ZnO film surface and the LC molecules, thereby subsequently achieving uniform and homogeneous LC alignment. The electro-optical (EO) characteristics of a twisted-nematic cell made with IB-irradiated In:ZnO film at an IB irradiation energy of 2200 eV, with which outstanding EO performance was observed. Therefore, using the solution-derived In:ZnO film with the IB irradiation as an alignment shows remarkable potential for use in LC device.

Liquid crystal aligning capabilities on surface-reformed indium-doped zinc oxide films via ion-beam exposure

ABSTRACTWe investigated the characteristics of a solution-processed indium-doped zinc oxide (In:ZnO) film formed via ion-beam (IB) irradiation as a liquid crystal (LC) alignment layer. The In:ZnO film was deposited using solution processing and cured at various temperatures. Uniform LC alignment was observed at all curing temperatures in cross-polarised optical microscopy images. A regular pre-tilt angle supported these results and showed homogeneous LC alignment. Several surface analyses were conducted to evaluate the effect of IB irradiation on the In:ZnO film surface. X-ray diffraction analysis showed an amorphous structure both before and after IB irradiation, and physical surface reformation was observed using atomic force microscopy. Root mean square surface roughness was reduced and a smooth surface was achieved after IB irradiation. X-ray photoelectron spectroscopy was used to detect chemical surface reformation. It was found that the IB irradiation broke the metal-oxide bonds and increased the occurrence of oxygen vacancies, which affected the van der Waals forces between the LC molecules and the In:ZnO film surface. Electrical performance was observed to identify the possibility of using the In:ZnO film in LC applications. Enhanced electro-optical performance was measured and zero residual DC voltage which was verified using a capacitance-voltage curve was achieved.

Growth and characterization of indium doped zinc oxide films sputtered from powder targets

Indium doped ZnO films were grown on quartz glass substrates by radio frequency magnetron sputtering from powder targets. Indium content in the targets varied from 1at% to 9at%. In doping on the structure, optical and electrical properties of ZnO thin films were studied. X-ray diffraction shows that all the films are hexagonal wurtzite with c-axis perpendicular to the substrates. There is a positive strain in the films and it increases with indium content. All the films show a high transmittance of 86% in the visible light region. Undoped ZnO thin film exhibits a high transmittance in the near infrared region. The transmittance of indium doped ZnO thin films decreases sharply in the near infrared region, and a cut-off wavelength can be found. The lowest resistivity of 4.3×10-4 Ω·cm and the highest carrier concentration of 1.86×1021 cm-3 can be obtained from ZnO thin films with an indium content of 5at% in the target.

Highly transparent and conductive indium-doped zinc oxide films deposited at low substrate temperature by spray pyrolysis from water-based solutions

In this paper, indium-doped zinc oxide (IZO) films were grown by spray pyrolysis, using zinc acetate and indium acetylacetonate precursors. The focus was on developing a solution recipe based on water as solvent, with only minor acetic acid content, as well as keeping the substrate temperature as low as possible—at 360 °C. The process is therefore environment friendly and energy efficient. Despite the challenging conditions, the resulting IZO films were highly transparent and conductive. Their texture deviates strongly from the (002) texture of ZnO and depends on the indium content, which also influences the resistivity. The latter attains its minimum for an indium concentration of 4 at.% in the solution and decreases for increasing film thickness, reaching the value of (5.0 ± 0.1) × 10−3 Ω cm, mainly due to the increase in carrier mobility. The stability of the resistivity after high dose of UV irradiation was found to increase with the carrier density and the film thickness. Thick, highly doped films show minimal resistivity modification even after a total dose of 12.1 kJ/cm2 UVA/UVB irradiation. Finally, to demonstrate its applicability in devices, the IZO electrode was used for the fabrication of a lead-perovskite absorber solar cell, yielding an energy conversion efficiency of 6% and 910 mV open-circuit voltage.

Solvothermal synthesis of indium-doped zinc oxide TCO films

This paper outlines the preparation of indium-doped zinc oxide films via solvothermal synthesis of nanoparticles, followed by spin coating of the transparent conductive oxide (TCO) layer. The effect of stabilizer type and its concentration on the suspension stability was studied. The influence of the In/Zn molar ratio (in the 0–0.06 range) on the lattice parameters and the cell volume was determined by XRD analysis. A linear change in these parameters was found, indicating a uniform integration of the indium into the ZnO crystal. Thermal analysis using TGA/DTA pointed to the optimal thermal treatment of the TCO layers at 500 °C. In addition, the effect of the molar ratio on the optical and electrical properties was studied. A minimal sheet resistance of 85 % at In/Zn = 0.04 were achieved. The above findings indicate that the solvothermal route can be very effective in the synthesis of state-of-the-art TCO coatings.

High conductivity indium doped ZnO films by metal target reactive co-sputtering

We report on the high conductivity indium doped zinc oxide (IZO) transparent thin films deposited by dc reactive co-sputtering of Zn and In targets with indium content varying from 0 to 3.2 at.%. In doping induced metal to semiconductor transition with transition temperature (TMS) decreasing to 100 K at 3.2 at.% In doping and resistivity (ρ) reaching to 3.60 × 10 −4 Ω cm. The ρ vs T behavior becomes linear in the 300–100 K regime and optical band-gap shows a blue-shift of 80 meV. A very high value of carrier concentration of 3.52 × 1021 cm−3 was reached without an associated increase in defect states. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) studies evidenced the reduction of oxygen vacancies (Vo) with incorporation of more indium in ZnO matrix at substitutional sites. Furthermore, XPS and PL studies affirmed that indium as donor is the main source of conductivity in these films. Our studies suggest that high ion energies available in dc sputtering mode with an associated enhanced surface migration and reactivity of ad-atoms is responsible for the efficient substitution of Zn2+ by In3+ and lowering of defects in these strongly (002) oriented highly crystalline IZO films. Lattice scattering dominates electron transport above TMS and ionized-impurity scattering prevails below it. Mobility shows weak temperature dependence in the temperature range 300–20 K.

Investigation of third order nonlinear optical properties of undoped and indium doped zinc oxide (InZnO) thin films by nanosecond Z-scan technique

We report the investigation of third order nonlinear optical properties of undoped zinc oxide and indium doped zinc oxide thin films using nanosecond (6ns, 18μJ at 532nm) Z-scan technique. Undoped (ZnO) and indium doped zinc oxide (InZnO) thin films were synthesized on quart silica substrate by using radio frequency (RF) magnetron sputtering technique. The structural and characterization of deposited thin films were analyzed by X-ray diffraction (XRD). In XRD results show different behaviors as amorphous oxide semiconductor and polycrystalline oxide semiconductor for ZnO and InZnO thin films respectively. Elemental compositions of thin films were analyzed by energy dispersive spectrometer (EDS). Surface morphology of ZnO and InZnO films were measured by using scanning electron microscopy (SEM), which show uniform and regular surface with small grain size distribution. Linear optical transmission and reflection thin films were analyzed by UV–VIS spectrometer. The UV–VIS results reveal that the optical transmittances of deposited thin films were increased after doping indium. The third order nonlinear optical properties of ZnO and InZnO thin films were carried out using nanosecond (6ns) laser Z-scan technique at 532nm wavelength. In open aperture case, both ZnO and InZnO thin films are show reverse saturable absorption (RSA) behaviors. For close-aperture Z-scan, the transmittance curve of ZnO thin film occurs as valley-peak (positive nonlinear refraction) characteristic, which indicates self-focusing behavior.

Structural and electrical characterizations of ZnO:In/PS/Si heterojunction deposited by rf-magnetron sputtering

Indium doped zinc oxide (IZO) thin film has been deposited on p-type porous silicon (PS) substrate by rf-magnetron sputtering of IZO aerogel nanoparticles at room temperature to obtain n-IZO/PS/p-Si heterojunction diode. The obtained IZO film, with a thickness of about 400 nm using indium concentration of 4 at.%, was polycrystalline with a hexagonal wurtzite structure and preferentially orientation in the (002) crystallographic direction. Atomic force microscopy (AFM) micrograph shows that IZO film has a typical columnar structure and a very smooth surface. The heterojunction parameters were evaluated from the current-voltage (I-V) characteristics carried out in the temperature range 80–300 K and capacitance-voltage (C-V) measurements. The ideality factor and barrier height of the heterojunction exhibited strong temperature dependence. The electrical measurements show that the n-IZO/PS/p-Si heterojunction has a Schottky electronic behavior where the depletion-layer is developed principally in the p-type silicon substrate. The tunneling mechanism via deep-level states was the main conduction process at low forward bias, while space-charge-limited current conduction dominated the carrier transport at higher bias. The I-V characteristics under illumination show that the p-n junction exhibits a photovoltaic behavior and is promising for photovoltaic application.

Effects of indium doping on the crystallographic, morphological, electrical, and optical properties of highly crystalline ZnO films

In this article, the authors have reported the growth and characterization of a batch of indium doped zinc oxide films to explore the controllable n-type doping in ZnO with high crystalline quality for the optoelectronic device application. The effects of indium doping on the crystalline structure, surface morphology, electrical, and optical properties have been shown. The mechanisms regarding the grain growth, the electron scattering, and the optical band gap have been investigated and discussed. The crystallite size is constrained by the competing effect between surface energy and lattice strain, and thus maintains invariable with increasing indium doping level. The coalescence of nearby crystallites leads to the growth of grains. The grain size has been found to increase with indium incorporation, suggesting that the surface diffusion rate of adatoms is enhanced by more indium. The increased Hall mobility can be explained by the reduced boundary effect, and can be also understood in the view of ion orbit radius and percolation conduction model. The band gap has been modified by the Burstein-Moss effect and the band gap renormalization effect. The band gap values of the samples with relatively higher indium doping level are dominated by the dopant-dependent band gap renormalization effect. This research provides a comprehensive understanding of the material properties of indium doped ZnO films grown by metal-organic chemical vapor deposition.

Fabrication and electrical properties of Si/PS/ZnO:In solar cell deposited by rf-magnetron sputtering based on nanopowder target material

Indium doped zinc oxide (IZO) nanopowder synthesized by sol–gel method has been grown onto p type porous silicon substrate by rf-magnetron sputtering at room temperature. The obtained IZO thin films with a thickness of about 400 nm using indium concentration of 4 at%, were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. Atomic force microscopy and scanning electron microscopy were used to study the films morphology. The obtained IZO films, generally used as TCO in solar cells, have a typical columnar structure and very smooth surface. From electrical characterizations: current–voltage (I–V) on dark and under illumination and capacity–voltage (C–V) at different frequency measurements, we can conclude that we have Schottky electronic behaviors where the depletion-layer is developed principally in p-type silicon region. The grown structure is promising for photovoltaic application.

Enhancement of the optical Kerr effect by photobleaching in nanostructured indium-doped zinc oxide thin films

A modification of the nonlinear refractive index exhibited by indium-doped zinc oxide thin solid films deposited by an ultrasonic spray pyrolysis technique, after strong femtosecond laser irradiation, is presented. We used a standard time-resolved optical Kerr gate configuration with 80 fs pulses at 830 nm in order to study the third-order optical nonlinearities of the samples. A significant enhancement of the optical Kerr response was obtained by intense femtosecond excitation, which induced a permanent bleaching in the sample. A quasi-instantaneous pure electronic nonlinearity without the contribution of nonlinear optical absorption was observed. There is a close relationship between the change in linear absorption induced in the indium-doped zinc oxide film after high-intensity irradiation and the strong third-order nonlinearity that develops in the irradiated film.

Preparation and Characterization of ZnO: In Transparent Conductor by Low Cost Dip Coating Technique

Transparent conducting oxide (TCO) based on indium doped zinc oxide films in the nano scale were successfully prepared using combination between dip coating and thermal decomposition process. Structural investigations confirm the polycrystalline ZnO hexagonal wurtzite phase grown along the c-axis with nano crystallite size about 10 nm. Morphology investigation shows that ZnO films consist of fine grains of average size 40 nm. This indicates that each grain contains several crystallites with different orientations. Cross sectional image presents good adhesion of the films with the substrate and the film thickness has been determined. Compositional analysis detects the indium content in the host ZnO matrix, the In/Zn ratio is close to the calculated concentration ratios of the precursor. The optical transmittance shows that the films are transparent in the UV and VIS-IR spectral region and interference fringes were observed to be thickness dependent. Preparation parameters were investigated and optimized such as dipping rate, number of deposition cycles, precursor concentration, annealing process and In/Zn ratio. Optimization process was investigated for low resistivity, high optical spectral window transmission and easy preparation process. Dipping rate in the range 2 - 38 mm/s is the most suitable range for good film quality while dipping rate range 30 - 38 mm/s produces thicker films in lower deposition cycles. The higher dipping rate produces films with lower transparency (milky films) while the small deposition rate rate requires large number of deposition cycles in order to increase the thickness. Besides, the higher dipping rate reflects lower resistivity of the deposited films. Precursor molar concentration was observed to have an essential effect on the film thickness, film quality and transparency. Lower precursor concentration requires also large number of deposition cycles for thickening the films. The higher concentration results also milky films (high scattering process by powder film). Precursor concentrations in the range 0.7 - 0.9 mol/liter were found to be the optimal for better quality and for faster deposition process. The resistivity of the films has been reduced from the range 1.5 - 2.5 kW?cm to the range 100 - 400 W.cm as the molar concentration reaches the range 0.07 - 0.09 mol/liter. The resistivity of films increases from 330 to 1686 .cm as the decomposition temperature increases from 200C to 350C. Annealing at 450C process after completing the decomposition at 200?C results the lowest resistivity with annealing time in the range 1.5 - 2 h. In/Zn percentage in the range 1.5% - 5% produces the lowest electrical resistivity. The absorption edge of the deposited films was observed to be critical affected by the preparation parameters. The band gap change was discussed through the degenerate semiconductors as well as nanostructured semiconducting materials of the energy gap confinement effect. Deposition of TCO based on ZnO:In was optimized depending on all deposition parameters forwide area, the lower cost and good performance TCO films.

The characterisation of aerosol assisted CVD conducting, photocatalytic indium doped zinc oxide films

Indium doped, and undoped, zinc oxide films were deposited using aerosol assisted chemical vapour deposition (AACVD) at atmospheric pressure on glass substrates. Electrical measurements ( I– V) showed a reduction in resistivity following the addition of indium, and XRD analysis revealed an associated switch to c-axis preferred crystal orientation. The ability of the films to oxidise organic material on their surface was analysed using stearic acid as the model contaminant under ultra-violet (UV, 365 nm) irradiation. The In-doped films displayed a greater rate of organic decomposition, which we attribute to the formation of a platelet surface structure having a larger surface area than the undoped films, on which the UV generated electrons and holes may react to form active photocatalytic species. In addition we suggest that the switch to c-axis crystal orientation may reduce the electron–hole pair recombination rate at the grain boundaries, due to an improvement in crystallinity and related reduction in carrier scattering losses, leading to an increase in photocatalytic organic decomposition rate.

Transparent conductive indium-doped zinc oxide films prepared by atmospheric pressure plasma jet

Atmospheric-pressure plasma processing has attracted much interest for industrial applications due to its low cost, high processing speed and simple system. In this study, atmospheric-pressure plasma jet technique was developed to deposit indium-doped zinc oxide films. The inorganic metal salts of zinc nitrate and indium nitrate were used as precursors for Zn ions and In ions, respectively. The effect of different indium doping concentration on the morphological, structural, electrical and optical properties of the films was investigated. Grazing incidence X-ray diffraction results show that the deposited films with a preferred (002) orientation. The lowest resistivity of 1.8 × 10 − 3 Ω cm was achieved with the 8 at.% indium-doped solution at the substrate temperature of 200 °C in open air, and average transmittance in the visible region was more than 80%.

Indium-Doped Zinc Oxide Thin Films as Effective Anodes of Organic Photovoltaic Devices

Indium-doped zinc oxide (IZO) thin films were prepared by low-cost ultrasonic spray pyrolysis (USP). Both a low resistivity (3.13×10−3 Ω cm) and an average direct transmittance (400∼1500 nm) about 80% of the IZO films were achieved. The IZO films were investigated as anodes in bulk-heterojunction organic photovoltaic (OPV) devices based on poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester. The device fabricated on IZO film-coated glass substrate showed an open circuit voltage of 0.56 V, a short circuit current of 8.49 mA cm-2, a fill factor of 0.40, and a power conversion efficiency of 1.91%, demonstrating that the IZO films prepared by USP technique are promising low In content and transparent electrode candidates of low-cost OPV devices.