Nitrogen and oxygen annealing effects on properties of aluminum-gallium oxide films grown by pulsed laser deposition

Aluminum-gallium oxide (AGO) films on c-plane sapphire substrates by pulsed laser deposition are described. Both nitrogen and oxygen annealing effects on the structural and optical properties of AGO films are investigated. The AGO film shows an amorphous structure when deposited at low temperatures (≤400 °C) while a crystalline structure at 800 °C. After post annealing at 900 °C, an amorphous-to-crystalline phase transformation for the 400°C-deposited film occurs and shows the preferred β phase. The corresponding optical bandgap also increases from 5.14 eV to 5.41–5.46 eV depending on the annealing ambience. From Raman measurements, the 800°C-deposited AGO sample possesses a more stable O–Ga–O bonding compared to that of the 400°C-deposited one after annealing. Unusually, an evident increase in the nitrogen content is observed for the samples after post annealing at 900 °C in nitrogen atmosphere. The rapid dissociation of oxygen atoms may accelerate the disintegration of crystals and rearrangement, which makes the AGO film adsorb nitrogen atoms and cause the grain size to be significantly reduced. However, the extent of the nitrogen incorporation seems to have no apparent effect on the optical properties. All the AGO films show the optical transmittance over 80% in the ultraviolet–visible region with the calculated bandgaps more than 5.4 eV. Details of the mechanism about the nitrogen incorporation into the annealed AGO films via the oxygen vacancies or micro-pores will be discussed.     

Indium-free large area Nb-doped SnO2 thin film as an alternative transparent conducting electrode

Niobium doped tin oxide (NTO) thin film deposited via facile chemical spray pyrolysis technique on to a large area (10 × 10 cm²) glass substrate exhibits better optical and electrical properties. The structural, surface, optical and electrical properties were analyzed by means of XRD, XPS, AFM, SEM-EDS, Hall Effect, and four-point probe techniques. The deposited NTO thin film was found to possess a maximum average transmittance value around 75% due to enhanced optical bandgap (3.77 eV) by Nb-dopant effect. The variation of sheet resistance of the large area (10 × 10 cm²) coated thin film over the entire region was studied at every 1 × 1 cm² area. The film doped with 1.5 wt% of Nb content showed improved carrier concentration (9.33 × 10¹⁹ cm^-3), higher free carrier mobility (39.4 cm²/V·s), improved electrical resistivity (1.69 × 10^-3 Ω cm) and low sheet resistance (26.5 Ω/□). The temperature dependent electrical measurement was carried out from 200 to 450 °C in steps of 50 °C to understand the resistance stability of the film. In addition to these studies, we report the surface work function of NTO thin film to identify its suitability in optoelectronic devices. The estimated electrical properties confirm the substitution of Nb⁵⁺ in Sn site of SnO₂ lattice. Our results indicate the optimized NTO thin film to possess promising optical and electrical transport properties to serve as a better indium-free alternate transparent conducting electrode in various optoelectronic devices.     

Fabrication of Pb(Zr,Ti)O3 thin films utilizing unconventional powder magnetron sputtering (PMS)

Pb(Zr,Ti)O3 (PZT) ferroelectric ceramic films exhibit highly superior ferroelectric, pyroelectric and piezoelectric properties which are promising for a number of applications including non-volatile random access memory devices, non-linear optics, motion and thermal sensors, tunable microwave systems and in energy harvesting (EH) use. In this research, a thin layer of PZT was deposited on two different substrates of Strontium Titanate (STO) and Strontium ruthenate (SRO) by powder magnetron sputtering (PMS) system. The preliminary powders, consisting of PbO, ZrO₂ and TiO_2, were manually mixed and placed into the target holder of the PMS. The deposition was performed at an elevated temperature reaching up to 600 °C via a ceramic heater. This high temperature is required for PZT thin film crystallinity, which is never achieved in conventional physical vapour deposition processes. The phase structure, crystallite size, stress-strain and surface morphology of deposited thin films were characterized using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The composition of the PZT thin films were also analysed by X-ray photoelectron spectroscopy (XPS). The mechanical properties of the thin films were evaluated with micro-scratch adhesive strength and micro hardness equipment. FESEM results showed that the PZT thin films were successfully deposited on both SRO and STO substrates. The surfaces of the coated samples were free from cracks, relatively smooth, uniform and dense. The profile of X-ray diffraction confirmed the formation of single-c-domain/single crystal perovskite phase grown on both substrates. The XPS analysis have shown that the PZT thin film grown by this method and that a target of PZT+10% PbO is a proper target for growing nominal PZT thin films. The adhesion strength and micro hardness results have confirmed the stability and durability of the thin film on the substrates, although higher values have been reported for thin film of PZT deposited on SRO surfaces.     

Molecular-solution printing of Cu2ZnSnS4 (CZTS) thin film

In this work, a novel molecular-solution printing approach combined with a rapid thermal annealing process for the facile fabrication of Cu₂ZnSnS₄ (CZTS) thin film is reported. The intrinsic relationship between annealing parameters (temperature and time) and the properties of the fabricated samples was investigated systematically. Furthermore, the mechanism behind this CZTS formation approach was studied in detail. The results show that the best properties were obtained for the sample annealed at 600 °C for 45 min, which displayed a pure kesterite CZTS phase, acceptable morphology consisting of 1.0–1.5 μm size nanoparticles, a satisfactory Cu-poor and Zn-rich composition, and an ideal bandgap of ~1.42 eV. Thus, the prepared sample is a promising candidate for the fabrication of high-performance photovoltaic devices.     

Ceramic–Ceramic Actuator Composed of Two Piezoelectric Layers with Opposite Poling Directions

A ceramic–ceramic actuator composed of two piezoelectric ceramic layers with opposite poling directions was developed. One layer of the actuator had a high coercive electric field (PZT (Pb(Zr,Ti)O₃)-I; E _c=1.1 kV/mm), while the other had a relatively low coercive electric field (PZT-II; E _c=0.6 kV/mm). The actuator was fabricated by cofiring a green compact composed of the PZT-I powder on top of the PZT-II powder. When an electric field >1.1 kV/mm was applied to the sintered body, the whole specimen was poled in one direction. Subsequently, by applying a field between 0.6 and 1.1 kV/mm, only the PZT-II layer was switched to the other direction. When an electric field was applied to this oppositely poled two-layer specimen, one layer of the specimen expanded while the other layer shrank. As a result of these reverse dilations, the actuator was bent into a dome shape, yielding a large axial displacement at the center. The displacement of this actuator with dimensions of 20 mm (diameter) × 1 mm (thickness) was 16 μm at 0.9 kV/mm.     

Enhanced optoelectronic properties of Ti-doped ZnO nanorods for photodetector applications

We report the effect of Ti-doping on structural, morphological, photoluminescence, optical and photoconductive properties of ZnO thin films. Pure and Ti(1, 3 and 5%)-doped ZnO thin films are deposited by the successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction analysis revealed the single-phase hexagonal wurtzite ZnO structure of all the films. Scanning electron microscope images suggest the formation of rod shaped particles in Ti-doped ZnO thin films. Photoluminescence spectra of all the films show emission peaks centered at 398 nm, 413 nm, 438 nm, 477 nm and 522 nm wavelengths. Optical properties support the semiconducting nature of all the films. The optical bandgap values are estimated to be 3.29 eV, 3.26 eV, 3.19 eV and 3.23 eV for ZnO, ZnO:Ti(1%), ZnO:Ti(3%) and ZnO:Ti(5%) thin films, respectively. Photoconductivity study indicates that ZnO:Ti(3%) thin film exhibits high responsivity, external quantum efficiency and detectivity of 0.30 AW^-1, 97% and 5.49 × 10¹⁰ Jones, respectively, among all the films. The enhanced photoconductivity of Ti-doped ZnO thin films make them useful for optoelectronic applications.     

Magnetic characteristics and optical band alignments of rare earth (Sm+3, Nd+3) doped garnet ferrite nanoparticles (NPs)

Yttrium iron garnet (YIG) nanoparticles (NPs) doped with rare earth (RE) metal ions (Y_2.5Sm_0.5Fe₅O₁₂, Y_2.5Nd_0.5Fe₅O₁₂) were successfully synthesized by sol-gel auto combustion approach. The cubic crystalline structure and morphology of the prepared garnet ferrite NPs were analyzed by X-ray diffractometer (XRD) and field emission scanning electron microscopy (FESEM). The cubic crystalline garnet phase of the synthesized YIG, Sm-YIG and Nd-YIG samples was successfully achieved at 950 °C sintering temperature. The force constant and absorption bands were estimated by using Fourier transform infrared spectroscopy (FTIR). The doping effect of RE metal ions on the chemical states of YIG were examined by x-ray photoelectron microscopy (XPS). The valence band (from 12.63 eV to 13.22 eV), conduction band (from 10.89 eV to 11.34 eV) edges and optical bandgap values of RE doped YIG samples were calculated using UV–Vis spectroscopy and ultraviolet photo electron spectroscopy (UPS). The magnetic analysis of the prepared NPs was studied using vibrating sample magnetometer (VSM). The XPS analysis of RE doped YIG samples exhibit the existence of RE (Sm⁺³, Nd⁺³) contents on the surface of YIG ferrite by decreasing the oxygen lattice in garnet structure. The optical bandgap (from 1.74 eV to 1.88 eV) explains the semiconducting nature of the synthesized NPs. The UPS results confirm the valence band position of YIG doped samples. The saturation magnetization and remanence of RE doped garnet ferrite samples increased from 13.45 to 18.83 emu/g and 4.06–6.53 emu/g, respectively.     

Corrosion behavior of electrodeposited Wo3 thin films

In this study, nanostructured tungsten trioxide (WO₃) thin films were deposited on Indium tin oxide (ITO)-coated glass substrate using electrochemical deposition (ECD). After deposition, the films were annealed at 450 °C for 2 h in an air atmosphere. X-ray diffraction (XRD) analysis confirmed that the prepared WO₃ thin films have crystalline phases. According to the absorption measurements, the optical bandgap of the WO₃ film was calculated as Eg 2.80 eV. Based on the scanning electron microscopy (SEM) images, the surface morphology of the thin films was influenced by deposition conditions. Raman spectroscopy analysis was also used to further examine the structure and chemical compositions of the thin films. The nature of the nanostructured WO₃ thin films was studied with Electrochemical Impedance Spectroscopy (EIS) and Tafel. Nyquist, open circuit potential and Bode analysis were used to evaluate structural changing and corrosion behavior of the prepared WO₃ thin films. With the help of these measurements and analyzes, the parameters such as solution resistance (Rs), polarization resistance (Rpo), a constant phase element (CPE) and a CPE exponent (n) were calculated as 43.43 Ω cm², 2.67 × 10⁶ Ω cm², 18.45 × 10⁻⁶ Ω⁻¹ s cm⁻², 0.958, respectively. Also, the corrosion features of the WO₃ thin films were investigated with the help of tafel measurements and the corrosion potential and current values were calculated as −0.583 V and 5.09 × 10⁻¹⁵ A, respectively. It is thought that the prepared thin film might have the potential to be used industrially with these features.     

Brookite and anatase nanomaterial polymorphs of TiO2 synthesized from TiCl3

Synthesis of anatase and brookite was achieved under mild conditions in aqueous solution. In addition, mixtures of brookite and rutile as well as mixtures of the anatase and rutile polymorphs were observed at different temperatures. It was observed that temperatures above 80 °C produced anatase and brookite phases, exclusively. The samples prepared using the acetate synthesis showed on average bandgap around 2.95–3.0 eV and brookite was observed. Whereas the samples prepared using the sulfate synthesis showed and bandgap from 3.1 to 3.2 eV and anatase was observed. In addition, the average grain size of the brookite and anatase phase synthesized at 100 °C were 9.7 and 12 nm, respectively, as determined from XRD.     

Effects of annealing temperature on the microstructure,optical, ferroelectric and photovoltaic properties of BiFeO3 thin films prepared by sol–gel method

Bismuth ferrite thin films were prepared via sol–gel spin-coating method and the effects of annealing temperature on microstructure, optical, ferroelectric and photovoltaic properties have been investigated. The results show that the bismuth ferrite thin films annealed at 550 °C is single phase and the grain size increases with the rise of annealing temperature. The band gap of bismuth ferrite thin films annealed at 550–650 °C is between 2.306 eV and 2.453 eV. With the rise of the annealing temperature, the remnant polarization gradually decreases and the coercive electric field increases. The short circuit photocurrent density decreases with the rise of annealing temperature, and the open circuit photovoltage and the power conversion efficiency of bismuth ferrite thin films annealed at 550 °C are higher than the thin films annealed at higher temperature.     

Electro-optical performances of nanostructured SrTiOx films: The effect of plasma power,Ar/O2 ratio and annealing

The present work evaluates the effects of plasma power and oxygen mixing ratios (OMRs) on structural, morphological, optical, and electrical properties of strontium titanate SrTiO_x (STO) thin films. STO thin films were grown by magnetron sputtering, and later thermal annealing at 700°C for 1 h was applied to improve film properties. X-ray diffraction analysis indicated that as-deposited films have amorphous microstructure independent of deposition conditions. The films deposited at higher OMR values and later annealed also showed amorphous structure while the films deposited at lower OMR value and annealed have nanocrystallinity. In addition, all as-deposited films were highly transparent (~80%–85%) in the visible spectrum and exhibited well-defined main absorption edge, while the annealing improved transparency (90%) within the same spectrum. The calculated direct and indirect optical band gaps for films were in the range of 3.60-4.30 eV as a function of deposition conditions. The refractive index of the films increased with OMRs and the postdeposition annealing. The frequency dependent capacitance measurements at 100 kHz were performed to obtain film dielectric constant values. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm² charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). The leakage current density was relatively low (3 × 10⁻⁸Acm⁻² at +0.8 V) indicating that STO films are promising for future dynamic random access memory applications.     

An Amalgam of Mg-Doped TiO2 Nanoparticles Prepared by Sol–Gel Method for Effective Antimicrobial and Photocatalytic Activity

In this study, undoped and Magnesium doped TiO₂ nanoparticles (Mg-TiO₂ NPs) are successfully synthesized via a simple sol–gel method cost-effectively. The prepared Mg- TiO₂ NPs is characterized by UV–Vis, FTIR, PL, XRD, FESEM, TEM, and EDAX. UV–Visible Spectroscopy showed that an increase in the optical bandgap concerning the concentration of dopant Mg increases. The bandgap values were found to be 3.57–3.54 eV. FTIR spectra shows that the presence of the characteristic stretching and bending vibrational band of Ti–O bonding at 468 cm^?1 and shifts in vibrational bands were observed for Mg-TiO₂ NPs. PL spectra of Mg- TiO₂ NPs at different concentrations exhibit a strong UV emission band. X-ray diffraction confirmed the formation of the tetragonal anatase phase. The average crystallite size of synthesized samples was found to be 22–19 nm. The average crystallite size of Mg- TiO₂ NPs decreases with increasing the concentration of dopant Mg. The FESEM and TEM analysis confirmed that the spherical morphology for both TiO₂ and Mg-TiO₂ NPs. SAED pattern confirms the crystalline nature of prepared samples. EDAX spectra confirm the presence of Ti, O, and Mg and confirm that Mg²⁺ ions are present in the TiO₂ lattices. The prepared samples were investigated against gram-positive and gram-negative bacteria. The prepared samples exhibit potent antibacterial activity against gram-negative bacteria than the gram-positive bacteria. The prepared samples exhibit significant photocatalytic degradation for Methylene blue (MB).

     

Insights into Cu2O thin film absorber via pulsed laser deposition

Cuprous oxide materials are of growing interest for optoelectronic devices and were produced by several chemical and physical methods. Here, we report on the structural, optical, and electrical properties of Cu_xO thin films prepared by the pulsed laser deposition technique. The substrate temperature, as well as the oxygen partial pressure in the deposition chamber, were varied to monitor the copper to oxygen ratio within the deposited films. The growth conditions were carefully optimized to provide the highest conductivity and mobility. Thus, 100 nm thick cuprous oxide films (Cu₂O) deposited at 750 °C exhibited a resistivity of 16 Ω?cm, high mobility of 30 cm²/(V?s), and a bandgap of around 2 eV. The film deposited at the optimized deposition parameters on Nb:STO (001) substrate with Au top electrode showed a photovoltaic response with an open circuit voltage of 0.56 V. These results path the way to efficient solar cells made with Cu₂O films via the pulsed laser deposition technique.     

Influence of annealing on the structural,optical and photoluminescence properties of ZnO thin films for enhanced H2 sensing application

Nanostructured zinc oxide (ZnO) thin film sensors were prepared by spray pyrolysis, and their structural, optical, photoluminescence and morphological properties were investigated by X-ray diffractometer, UV–vis spectrometer, photoluminescence spectrometer, and scanning electron microscope (SEM), respectively. The post-annealing of ZnO film in air at 400 °C was found to be effective for the distribution of grains and their sizes, which favors the c-axis orientation of the film. This enhancement is accompanied by an increase in the optical band gap from 3.4 eV to 3.53 eV, which confirms the uniformity of ZnO film prepared by using a specially designed spray nozzle. SEM micrograph after heat treatment revealed uniform distribution of particles with well grown grains of ZnO. Hydrogen sensing measurement indicated the annealed ZnO film to show much higher response than the as deposited film. To understand the enhancement of the sensing performance of the annealed ZnO film, the gas sensing mechanism of the film was proposed and discussed. The magnitudes of the sensor response as well as its dependence on annealing differ significantly depending on the crystallite size of the film.     

Direct Formation and Luminescence Properties of Yttrium Niobate YNbO4 Nanocrystals via Hydrothermal Method

Yttrium niobate YNbO₄ nanocrystals with ellipsoidal morphology were directly formed from the precursor solution mixtures of YCl₃ and NbCl₅ under weakly basic conditions in the presence of aqueous ammonia by hydrothermal method. The hydrothermal treatment at 180°C for 5 h was necessary to obtain nanocrystals (18 nm) with sufficient crystallinity. The optical band gap of the as‐prepared samples was 3.6 eV. The as‐prepared YNbO₄ nanocrystals showed UV‐blue and broadband emission centered at 405 nm under excitation at 235 nm, which was due to the blue recombination luminescence, associated with charge‐transfer transitions involving the tetrahedral NbO₄ group. The emission intensity increased with increased hydrothermal treatment temperature. The photoluminescence intensity of the YNbO₄ was extremely improved via heating above 1000°C in air, which was accompanied by the increase in the optical band gap from 3.6 to 4.0 eV. By heat treatment at 1300°C, the intensity of the UV‐blue and broadband emission (with maximum at 400 nm) for the YNbO₄ became more than 22.5 times as strong as that before heat treatment.     

Investigation of photocatalytic and luminescence properties of Na0.5Ce0.5WO4 self-assembled photocatalysts under solar light irradiation: Morphological,temperature and pH role

Tungstate-based scheelite structures have attracted much attention for the photocatalytic, adsorption and luminescence. To improve their performance, several ways have been considered, such as morphology control, thermal treatment and nanostructuring materials. In this work, three uniform and homogeneous morphologies, such as spindles, spheres and flowers, of self-assembled three-dimensional Na_0.5Ce_0.5WO₄ were used as photocatalysts for methylene blue dye photodegradation under solar irradiation. Depending on morphology, they required different temperatures to reach crystallization. Thermal treatments at 500 °C and 800 °C resulted in changes in crystallite size, porosity, surface state, but also in bandgap and emission properties. Thus, the crystallite sizes are about 50 nm for samples (spindles and flowers) treated at 500°Cand 87–167 nm for those treated at 800 °C. Their respective bandgap values measured by diffuse reflectance were 2.85 eV beyond 3.15 eV. The samples treated at 500 °C showed a lower emission and a longer charge carrier lifetime. A strong trend to adsorption was revealed, especially at low pH value and for the samples treated at 500 °C, reaching 100% at a pH value of 2.5. With decreasing pH, the photocatalysis activity increases (up to 50%), being also more efficient with catalysts treated at low temperature. It follows that the degradation efficiency of spindles treated at 500 °C is clearly higher compared to other morphologies treated at different temperature, and suitable for solar photocatalysis.     

Improved photoluminescence emission and gas sensor properties of ZnO thin films

In this article, we report a comparative study of the influence of pressure-assisted (1.72 MPa) versus ambient pressure thermal annealing on both ZnO thin films treated at 330 °C for 32 h. The effects of pressure on the structural, morphological, optical, and gas sensor properties of these thin films were investigated. The results show that partial preferential orientation of the wurtzite-structure ZnO thin films in the [002] or [101] planes is induced based on the thermal annealing conditions used (i.e., pressure assisted or ambient pressure). UV–vis absorption measurements revealed a negligible variation in the optical -band gap values for the both ZnO thin films. Consequently, it is deduced that the ZnO thin films exhibit different distortions of the tetrahedral [ZnO₄] clusters, corresponding to different concentrations of deep and shallow level defects in both samples. This difference induced a variation of the interface/bulk-surface, which might be responsible for the enhanced optical and gas sensor properties of the pressure-assisted thermally annealed film. Additionally, pressure-assisted thermal annealing of the ZnO films improved the H₂ sensitivity by a factor of two.     

Nonlinear growth of zinc tin oxide thin films prepared by atomic layer deposition

Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO₂ processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO_x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV.     

Low‐Temperature Deposition of Hexagonal Boron Nitride via Sequential Injection of Triethylboron and N2/H2 Plasma

Hexagonal boron nitride (hBN) thin films were deposited on silicon and quartz substrates using sequential exposures of triethylboron and N₂/H₂ plasma in a hollow‐cathode plasma‐assisted atomic layer deposition reactor at low temperatures (≤450°C). A non‐saturating film deposition rate was observed for substrate temperatures above 250°C. BN films were characterized for their chemical composition, crystallinity, surface morphology, and optical properties. X‐ray photoelectron spectroscopy (XPS) depicted the peaks of boron, nitrogen, carbon, and oxygen at the film surface. B 1s and N 1s high‐resolution XPS spectra confirmed the presence of BN with peaks located at 190.8 and 398.3 eV, respectively. As deposited films were polycrystalline, single‐phase hBN irrespective of the deposition temperature. Absorption spectra exhibited an optical band edge at ~5.25 eV and an optical transmittance greater than 90% in the visible region of the spectrum. Refractive index of the hBN film deposited at 450°C was 1.60 at 550 nm, which increased to 1.64 after postdeposition annealing at 800°C for 30 min. These results represent the first demonstration of hBN deposition using low‐temperature hollow‐cathode plasma‐assisted sequential deposition technique.     

Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.