Indium Doped ZnO Thin Films Research Articles

Blue luminescence of indium-doped ZnO thin films prepared by DC magnetron sputtering

ZnO is an intrinsic semiconductor suitable for many optical applications. In this current study homemade DC magnetron sputtering was used to grow undoped ZnO and indium-doped ZnO (or IZO) thin films. The indium content was varied from a mole fraction ratio of In2O3 were 0 at% to 6 at%. The structure of IZO films analyzed by X-ray diffraction (XRD), and the optical properties were carried out using UV-visible and photoluminescence (PL) spectroscopies. The XRD results demonstrated that IZO maintained a hexagonal wurtzite structure with a (002) preferential orientation. The optical band gap increased with an increase in indium doped concentration. The PL spectrum exhibits a broadband blue emission from IZO films centered at 440 nm (2,82 eV), originating from the radiative recombination at the defect level. Interestingly, the intensity of blue emission increased with an increase in indium-doped concentration.

Fabrication of In doped ZnO thin films by spray pyrolysis as photoanode in DSSCs

Highly compact and transparent pristine ZnO and indium doped ZnO (IZO) thin films have been successfully deposited on ITO substrates and their performance as photoanode in DSSCs were investigated. The structural analysis confirmed the wurtzite structure of ZnO with preferential orientation (002). The FESEM images depicted the granular and porous structure for the pristine ZnO and the nanofiber network structure for the IZO thin films. The porous nature with smaller roughness measured by AFM was the essential factors for achieving high performance in photovoltaic applications. IZO films showed high optical transmittance in the visible region. A minimum resistivity of 1.22 × 10−3 Ω cm and highest electron concentration of 10.74 × 1019 cm3 were achieved for 1.5 at.% of In dopant. The photovoltaic performance of IZO as a photoanode in DSSCs showed the highest power conversion efficiency of 1.09%. The preparation temperature and the solvent used for the preparation of natural dye were optimized to increase the efficiency of the solar cell.

Thermal evolution of point defects in indium doped ZnO transparent conducting films

High visible light transparency and conductivity of ZnO enable the use of its material as transparent conducting films, in which point defects are vitally important for determining its optoelectronic properties. Herein, Indium doped ZnO thin films (ZnO:In) were prepared by radio-frequency magnetron sputtering technique. Thermal evolution of point defects and their effects on the microstructure and photoelectric properties of ZnO:In transparent conducting films were systematically investigated. The results show that thermal annealing induces the dissociation of extensive zinc interstitial clusters, causing their concentration gradually decreasing with increasing annealing temperature. Furthermore, when annealing at low temperature (≤ 500°C), the concentration of oxygen vacancy and zinc vacancy defects also decreases with increasing temperature. However, after annealing at higher temperature (600 and 700°C), additional vacancy defects are generated due to the evaporation of zinc and oxygen atoms from the film surface. It is demonstrated that the evolution of point defects caused by thermal annealing directly affects the microstructure and photoelectric properties of ZnO:In transparent conducting films.

Development of indium doped ZnO thin films for highly sensitive acetylene (C2H2) gas sensing

Abstract The proposed article presents optimized Indium doped ZnO thin film for acetylene gas sensor. Thin films of ZnO and Indium doped ZnO of thickness 100 nm were successfully deposited on glass substrate using resistive thermal evaporation method. Structural properties have been performed by using XRD which reveals polycrystalline nature of the thin films. Morphological studies have been performed by using FESEM which reveals the information that thin film is homogeneous and uniform. AFM showed that with the increasing of indium doping concentration in ZnO resulting increment in vertical roughness of thin films. Further sample were tested for acetylene gas sensing using Keithley source meter and multimeter. The fabricated sensor (IZO-3) showed high sensitivity magnitude of 29.06 (100 ppm), short response and recovery time of 49.28 s and 58.45 s respectively at 150 °C operating temperature. IZO-3 sensor showed good linearity with good selectivity and excellent reproducibility.

Analysis of structural, optical and electrical properties of nano-particulate indium doped zinc oxide thin films

Indium doped ZnO thin films were deposited on glass substrates by spray pyrolysis technique with variation of indium concentration within a range of 0–5 at% and annealed at 500 °C for 2 h in presence of air. Preferentially oriented ZnO films along (002) plane has been obtained at 1 at% indium doping concentration. The particle size is found to be decreased with increase in dopant concentration as a result of lowering of cohesion in ZnO. The 5 at% indium doped ZnO film has a better compact morphology due to better grain boundary interactions for which it shows highest hall mobility in comparison to the all concentration of indium doped samples. The marginal band gap shift with In doping is attributed to Burstein-Moss shift. Highest thermal activation energy of 0.78 eV has been observed in case of 3 at% indium doping. The origin of the observed visible emission peaks at 450 nm, 468 nm, 480 nm, 490 nm and 670 nm are ascribed to various defects present within the bandgap.

The effect of indium doping concentration on the electrical and dielectric properties of Al/In:ZnO/p-Si heterojunctions

Undoped and 0.1% 0.5% and 1.0% indium doped ZnO thin films were obtained by spin coating method as interfacial thin film layer between Al metal and p-Si semiconductor to investigate dielectric properties of the Al/In:ZnO/p-Si heterojunctions. Impedance spectroscopy technique was employed to characterize the dielectric properties of the Al/In:ZnO/p-Si heterojunctions depending on frequency (from 10 kHz to 1 MHz) and voltage (from −5 V to +5 V). The results imparted that interface states (Nss), series resistance (Rs), barrier height (Φb) and the concentration of acceptor atoms (Na) influenced frequency changes. The dielectric parameters such as dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ), real and imaginary parts of the electric modulus (M′ and M″) and ac electrical conductivity (σ) values were calculated from impedance spectroscopy measurements and discussed in details for changing frequency and voltage for various In doped ZnO thin film interlayers. The dielectric properties of the Al/In:ZnO/p-Si heterojunctions were affected both In doping concentration and the frequency and voltage changes. The Al/In:ZnO/p-Si heterojunctions can be considered for industrial applications to increase the control.

Solution-processed undoped and Indium doped ZnO thin film transistors: role of Ag nanowires into InZnO channel layer

We report solution-processed undoped ZnO, 1 at% In doped ZnO (IZO) and 1 at% Ag nanowires (AgNWs) embedded IZO thin film transistors (TFTs). The mobility of prepared TFTs was enhanced compared to undoped ZnO, and AgNWs embedded IZO TFT exhibited excellent electrical performances with high field-effect mobility of 38.17 cm2V−1s−1 and high on/off current ratio on the order of 107. The energy dispersive x-ray (EDX) elemental mapping and x-ray photon spectroscopy (XPS) analysis demonstrated that the Ag particles are diffused into IZO thin film from AgNWs, suggesting that AgNWs played dual role in the channel layer which served as an acceptor charge carrier and a conductive path for charge carriers. SEM images showed that IZO film had increased grain size in comparison to undoped ZnO film and that AgNWs were well interconnected IZO film. The increment in the grain size in the IZO film and well connected AgNWs in the IZO films lead to enhanced mobility of the TFTs.

Enhanced gas sensing properties of indium doped ZnO thin films

Indium doped ZnO (InxZn1-xO, 0 ≤ x ≤ 0.05) thin films were deposited on to soda lime glass substrate by employing spray pyrolysis as deposition technique. Effect of doping concentration on characteristics of thin films were examined by XRD, SEM, UV-Visible spectroscopy, electrical and gas sensing measurements. XRD analysis demonstrates polycrystalline nature of thin films and also shows the shift in orientation from (002) to (101) crystal plane with increase in indium doping concentration. Surface morphological analysis shows the formation of homogeneous particle like nanostructures. Optical transmittance determined from UV-Visible spectroscopy was in the range of 80–95%, which was decreasing with increase in indium doping concentration. Maximum electrical conductivity was achieved at an optimal indium doping concentration of 3 at.%. The gas sensing properties were examined for different concentration of volatile organic compounds like acetone, ethanol and methanol for different doping levels. In0.03Zn0.97O thin films showed good sensitivity towards ethanol, with sensitivity of 30% towards 25 ppm of ethanol.

Study of Undoped and Indium Doped ZnO Thin Films Deposited by Sol Gel Method

In this paper, we report the effects of Indium doping concentrations (from 0 to 10wt%) on the structural, morphological, and optical properties of deposited In doped ZnO (IZO) thin films prepared by the sol–gel method through the dip coating technique. X-ray diffraction (XRD) analysis indicates that all ZnO thin films have a polycrystalline nature with a hexagonal wurtzite phase with (002) as a preferential orientation. XRD results demonstrate that the particle size of ZnO decreased with the increase in Indium concentrations. Raman scattering spectra confirmed the wurtzite phase and the presence of intrinsic defects in our samples. Energy dispersive spectroscopy (EDS) and the X-ray photoelectron spectroscopy (XPS) measurements, confirmed the presence of zinc, oxygen and indium elements which is in agreement with XPS results. The photoluminescence (PL) spectra of the films exhibit defects-related visible emission peaks, with intensities differing owing to different concentrations of zinc vacancies. UV–Vis spectrometer measurements show that all the films are highly transparent in the visible wavelength region (≥ 70%) and presented two different absorption edges at about 3.21 eV and 3.7 eV, these may be correspond to the band gap of zinc oxide and indium oxide respectively.

Some physical properties of n-IZO/p-CuO thin film heterojunction diodes completely made by spray pyrolysis

In order to produce an indium-doped ZnO/CuO thin film diode using spray pyrolysis, a high-quality indium-doped ZnO thin film with the resistivity of 5.65 × 10−3 Ω cm and the average transparency of 90% (400–800 nm) was first spray-deposited onto a glass substrate. Then, a p-type CuO layer was spray-deposited on top of the indium-doped ZnO film and the deposition temperature was varied from 300 to 400 °C with 25 °C steps (named IC1–IC5). The structural, morphological, and optical properties of both indium-doped ZnO and CuO thin films were studied. In addition, the current–voltage characteristics of the resulting IZO/CuO samples were recorded at room temperature and dark condition from − 1.5 to 1.5 V. Apart from IC1 and IC5 samples, the IV characteristics of the other samples showed an exponential attitude which confirmed the formation of heterojunction diodes. Diode parameters were calculated for the aforementioned heterojunction using thermionic emission theory. It was found that as the deposition temperature of the CuO layer increases, the barrier height remains almost unchanged, the rectifying ratio increases, and the series resistance reduces drastically. The estimated ideality factors were significantly larger than 1, which is indicative of the non-ideal attitude of the resulting diodes.

Investigation of the optical properties of the indium-doped ZnO thin films deposited by a thermionic vacuum arc

In this paper, the investigation of optical properties of an indium-doped ZnO (IZO) thin films deposited on glass and polyethylene terephthalate (PET) by thermionic vacuum arc technique were done. Also, the surface, structural and electrical properties of deposited films were studied by an atomic force microscopy (AFM), field emission electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible (UV–vis) spectrophotometer, interferometer and Hall effect system. Using a Filmetrics F20 thin film measurement system, the thickness values of the deposited IZO thin films were obtained as to be 110nm and 190nm on glass and PET substrates, respectively. All IZO films are in a polycrystalline structure. The estimated mean crystallite size values were recorded as 29.34nm and 28.17nm on the glass and PET substrates, respectively. The surface images of the FESEM analysis show growth of granular structure on the surface and the results are in good agreement with AFM results. Using UV–vis spectrophotometer and interferometer, the refractive index, reflectance, transmittance, absorbance and optical band gap of the deposited films were determined. The calculated optical band gap values of the films are obtained as to 3.64eV and 3.55eV for glass and PET substrate, respectively. The electrical measurements show that sheet resistance is dependence on the substrate materials.

Indium Doped ZnO Thin Films Prepared by Sol–Gel Technique for Efficient Inverted Type of Polymer Solar Cells

Indium Doped ZnO Thin Films Prepared by Sol–Gel Technique for Efficient Inverted Type of Polymer Solar Cells

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.

The effects of indium precursors on the structural, optical and electrical properties of nanostructured thin ZnO films

The polycrystalline transparent indium doped ZnO thin films (IZO) were deposited on the glass substrate using simple dip coating technique. Different types of indium precursors such as its nitrate, chloride and acetate were used as doping sources to prepare the IZO films. The effects of In precursor on structural, optical and electrical properties of nanostructured thin IZO films were investigated for the first time and compared with pure ZnO thin film. It was found that the type of indium precursors and the nature of the used salts have an important parameter to control the properties of IZO thin films. Experimental results showed that the prepared thin film by using indium nitrate precursor exhibits higher crystallinity and optical transmission with lower resistivity (2.2×10−3Ω.cm−1) in comparison with those films prepared using other precursors and can be useful in fabricating transparent electrodes.

The electrical stability of In-doped ZnO thin films deposited by RF sputtering

The electrical stability of transparent conductive oxides is an important criterion for evaluating their performance, especially when they are employed at elevated temperatures or in long-term operation. In this work, indium-doped ZnO thin films with various doping concentrations were prepared by RF sputtering. The electrical properties, electrical thermal stability, and time stability of films with differing indium contents were investigated. The results showed that the degradation of the films’ conductivity is primarily attributable to the reduction in oxygen vacancies at high temperatures under oxygenated conditions. The aggregation of indium atoms, which cannot replace Zn3+ cations at temperatures above 200 °C, can improve the carrier concentration. Further reaction with oxygen degraded the performance of the films due to the formation of insulating oxides. Long-term analysis showed the IZO films to have quite stable electrical properties. Their conductivity remained almost unchanged after two months at room temperature under normal atmospheric conditions.

Thermoelectric Properties of Indium and Gallium Dually Doped ZnO Thin Films.

We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants' radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

A Comparative Study the Calculation of the Optical Gap Energy and Urbach Energy in Undoped and Indium Doped ZnO Thin Films

In the present paper, we investigated a new model by theoretical methods; it is based on correlation from the experimental data’s which was used in the calculation the optical gap energy and Urbach energies. These data’s were taken from papers previously published. The choice ZnO thin films and spray only to compare our models with the Indium doping. From obtained relations found that the experimental data and theoretical calculation are in qualitative, which were supported with the variation of solution molarities and Indium doping. We have obtained a high correlation coefficient in the estimation of the band gap energy is higher than 0.96 with compare of Urbach energy is changed from 0.84 to 0.89. The measurements by these new models have agreed with minimum relative errors, it is found in the calculations of optical band gap does not exceed 4 %, and for Urbach energy are smaller than 20 and 10 % for undoped and Indium doped ZnO films, respectively. So that the best estimation was found at the Indium doped ZnO thin with maximum enhancement of minimum errors were limited to 3.5 and 9.7 % for the band gap and the Urbach energies, respectively. The decreases in the relative errors of undoped to Indium doped films can be explained by the fewer defects and less disorder.

Properties of indium doped nanocrystalline ZnO thin films and their enhanced gas sensing performance

Enhancement of gas sensing performance of indium doped ZnO thin film at optimal indium concentration as compared to its undoped counterpart.

Correlation in calculations of electrical conductivity with and without undoped in Al, Co and In doped ZnO thin film

The transparent conductive pure and doped zinc oxide thin films with aluminum, cobalt and indium were deposited by ultrasonic spray technique on glass substrate at 350°C. This paper is to present a new approach to the description of correlation between electrical conductivity and crystallite size with dopant concentration of Al, Co and In. The correlation between electrical and structural properties with dopant concentration suggests that the electrical conductivity of the films is predominantly estimated by the crystallite size and the concentration of Al, Co and In. The measurement in the electrical conductivity of doped films with correlation is equal to the experimental value of without undoped ZnO thin films, here the error is limited to zero %. The minimum error value was estimated in the cobalt and indium doped ZnO thin films. The correlation between the electrical conductivity and the crystallite size with the doping concentration was investigated.

N- to p- type carrier reversal in nanocrystalline indium doped ZnO thin film gas sensors

Selectivity has been the central issue in the research area of semiconducting metal oxide gas sensors and still remains a challenge for the researchers. In the present work, we report a promising hydrogen (reducing gas) sensing characteristics of nanocrystalline indium doped zinc oxide thin film sensing elements. At sensor operating temperature in the range (200–300) °C, ‘n’ to ‘p’ type carrier reversal is detected in the measured resistance transients. Furthermore, for a given operating temperature the type of carriers remain unaltered for each concentrations of gas. Thus, temperature plays a crucial role for this transition irrespective of the gas concentration. However, such carrier reversal is not observed in NO2 (oxidizing gas) environment even with the variation of operating temperature and gas concentration. This is attributed to the gas sensing mechanism related to the surface conductivity and the underlying variations of the carrier type. It is argued that, it can pave the way for selective detection of hydrogen at lower operating temperatures.