Indium Oxide Thin Films Research Articles

Advancement of Electro-Optical Properties through Changes in the Physicochemical Composition of Hybrid Thin Films by Doping Reduced Graphene Oxide into a Sol-Gel Process Solution.

A hybrid thin film was fabricated by doping graphene oxide into a sol-gel solution containing a mixture of zirconium, bismuth, and indium oxide. The thin film was fabricated using a brush coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt%. During the thin film fabrication process, the produced sol-gel solution generates a contractile force due to the shear stress of the brush bristles, resulting in a microgroove structure. This structure was confirmed through scanning electron microscopy analysis, which revealed the clear presence of rGO. Comparing the electrical properties of a zirconium bismuth indium oxide thin film without graphene oxide doping and a thin film doped with 15 wt% graphene oxide, the electro-optical properties were significantly improved with graphene oxide doping. In general, the threshold voltage decreased by approximately 0.42 V. In addition, bandgap measurements confirmed the improved conductivity characteristics with graphene oxide doping. Since this improvement in electro-optical properties is associated with the reduction process due to graphene oxide doping, X-ray photoelectron spectroscopy analysis was performed to assess the intensity change of each element. Based on these observations, hybrid thin films doped with graphene oxide emerge as promising candidates for next generation thin film.

Multi-Functional Molybdenum Oxide Doping to Improve the Electrical Characteristics of Indium Oxide Thin Film Transistors

Multi-Functional Molybdenum Oxide Doping to Improve the Electrical Characteristics of Indium Oxide Thin Film Transistors

Tolerance of Corundum‐Structured Tin‐Doped Indium Oxide Thin Films to Gamma‐ray Irradiation

Corundum‐structured Sn‐doped indium oxide (rh‐ITO) is investigated as a novel transparent conductive oxide. Herein, its gamma‐ray tolerance up to a total dose of 77 kGy is examined for potential applications in harsh environments, such as space. The investigations are conducted on rh‐ITO with Sn concentrations of 0 and 5 at%. X‐ray diffraction 2θ‐ω scan analysis reveals that no phase separation occurs due to gamma‐ray irradiation. The carrier concentration in undoped rh‐In2O3 increases after irradiation, indicating that the gamma rays displace the oxygen atoms and form oxygen defects that generate donors. The high visible light transparency of rh‐In2O3 and rh‐ITO is maintained after irradiation. This study demonstrates the high stability of rh‐ITO to gamma‐ray irradiation until 77 kGy dose. This work contributes to the application of rh‐ITO as an electrode in high‐radiation environments.

High-sensitive and fast-responsive In2O3 thin film sensors for dual detection of NO2 and H2S gases at room temperature

In this work, the room-temperature dual gas sensing characteristics of indium oxide (In2O3) thin films towards NO2 and H2S have been studied. In2O3 thin films were synthesized by the thermal oxidation of indium metal films of various thicknesses in the range of 50–250 nm deposited by thermal evaporation method. Grazing incidence X-ray diffraction (GI-XRD) revealed the change in preferred orientation of In2O3 thin films corresponding to varying thickness, while field-emission electron microscopy studies showcased evolving surface morphologies from individual grains to granular network with respect to the increase in film thickness. Investigations were made on the ability of In2O3 thin films to detect various low concentrations of nitrogen dioxide (NO2) and hydrogen sulfide (H2S) gases at ambient temperature. In2O3 thin films synthesized using 100 nm thick In films exhibited good sensing response of around 58 and 68 % towards NO2 and H2S gases of 5 ppm respectively, at room temperature (27 °C) with the response time of 36 and 18 s. Remarkably, the lower experimental detection limit of these toxic gases could be extended up to 100 ppb. Using X-ray photoelectron spectroscopy, a large presence of surface oxygen is observed on the In2O3 thin film. The sensor has demonstrated remarkable sensing abilities, including strong selectivity, quick sensing response, and good repeatability.

Reliable Operation in High-Mobility Indium Oxide Thin Film Transistors.

Transparent oxide semiconductors (TOSs) based thin-film transistors (TFTs) that exhibit higher field effect mobility (µFE) are highly required toward the realization of next-generation displays. Among numerous types of TOS-TFTs, In2O3-based TFTs are the front-running candidate because they exhibit the highest µFE ≈100cm2V-1s-1. However, the device operation of In2O3 TFTs is unreliable; a large voltage shift occurs especially when negative gate bias is applied due to adsorption/desorption of gas molecules. Although passivation of the TFTs is used to overcome such instability, previously proposed passivation materials do not improve the reliability. Here, it is shown that the In2O3 TFTs passivated with Y2O3 and Er2O3 films are highly reliable and do not show threshold voltage shifts when applying gate bias. Positive and negative gate bias is applied to the In2O3 TFTs passivated with various insulating oxides and found that only the In2O3 TFTs passivated with Y2O3 and Er2O3 films do not exhibit threshold voltage shifts. It is observed that only the Y2O3 grew heteroepitaxially on the In2O3 crystal. This is the origin of the high reliability of the In2O3 TFTs passivated with Y2O3 and Er2O3 films. This finding accelerates the development of next-generation displays using high-mobility In2O3 TFTs.

Intrinsic doping and ageing of indium oxide thin films

Indium oxide (In2O3) is one of the most used materials for the synthesis of transparent electronics devices and currently tin-doped indium oxide (ITO) dominates the field of Transparent Conductive Oxides for most applications, from ICT to photovoltaics. In this work we present a study on the responses of indium oxide upon the formation, and stabilization, of point defects induced with different methods. After the deposition of In2O3 thin films via RF magnetron sputtering, treatments such as Ion Implantation (I.I.), Ultraviolet (UV) irradiation and Sun exposure were employed to generate oxygen vacancies as intrinsic dopants. Both I.I. and UV irradiations significantly improved the electrical conductivity of films, increasing the carrier density by up to 3 orders of magnitude. Moreover, after I.I. also the crystalline quality of the films was enhanced.To monitor the stability of oxygen vacancies upon exposure to ambient atmosphere, the ageing of samples was followed and recorded for a couple of weeks, reporting a fast and strong degradation of electrical properties. As a facile strategy to counteract the sheet resistance increase, samples were encapsulated in an ultra-thin (≈10 nm) SiO2 layer deposited via sputtering. Irradiated and encapsulated films retained a much lower sheet resistance throughout the observation time, preserving the samples conductivity.

Aqueous solution-processed In2O3 TFTs using focused plasma in gas mixtures

Solution-processed indium oxide (In2O3) thin films have been studied widely as active layers for transparent semiconducting devices because of their high charge carrier concentration, low absorbance, simple fabrication methods, and low cost. Several studies on improving the electrical characteristics of thin-film transistors (TFTs) by optimizing and fine-tuning the fabrication process and using various post-deposition treatments have been conducted to take full advantage of these semiconductor films in high-performance electronics. This study examined the effects of a focused plasma (FP) treatment on In2O3 thin films prepared using a simple solution process at 250 °C. The effects of the FP generated from N2 gas and two gas mixtures (N2-H2 and N2-H2-O2) on the electrical performance of the TFTs were analyzed. The FP treatment enhanced the electrical properties of the device, and the specific performance and stability parameters were improved by the treatment conditions. X-ray photoelectron spectroscopy showed that the FP treatment could effectively control the oxygen vacancies and carrier concentration in the solution-processed In2O3 thin films. Therefore, an FP beam is a viable method for optimizing In2O3 TFTs prepared at low temperatures for application in high-performance transparent electronic devices.

Realization of high transparent mobility zinc‐doped indium oxide (IZO) thin films by RF‐magnetron sputtering

AbstractZinc‐doped indium oxide (IZO) thin films were deposited on silicon dioxide substrates by radio‐frequency magnetron sputtering using an IZO ceramic target with In2O3/ZnO weight ratio of 9:1. The effects of power, pressure, and distance between target and substrate on microstructure and photoelectric properties of IZO films were investigated. The results show the performance of IZO films prepared under the conditions of power 80 W, air pressure .5 Pa, and target base distance 80 mm are the best, and the IZO films are amorphous with high transmittance (>86.0%), high mobility (>45.0 cm2/V s), and low resistivity (less than 2.0 × 10−4 Ω cm), which are the best photoelectric performance reported at present. This work provides a feasible research approach for preparing high‐performance IZO thin films.

Investigation of optoelectronic properties of tin-doped indium oxide thin films and contact resistivity with silver film: Role of oxygen concentration variation during sputter deposition

We have investigated the optoelectronic properties like carrier concentration (NITO), mobility (µITO), work function (ϕITO), optical transmission and constants, and sheet resistance (Rsh) of tin-doped indium oxide (ITO) films with the variations in the oxygen flow rate during reactive sputter deposition with the Ar:O2 plasma. Initially, we also analyzed the generated Ar:O2 plasma parameters (ion energy and density, electron temperature, and energy distribution) using the Langmuir probe. The ITO films' optoelectronic properties were investigated systematically in as-deposited and annealed (150 to 200 °C) conditions with varying O2 flow rates. By varying the O2 flow rate, we observed the carrier mobility (µITO) of the ITO films in the range of 31-47 cm²/V-s, carrier concentration (NITO) in the range of 2.16 × 1019 - 5.22 × 1020 cm−3, and resistivity in the range of 3.57 × 10−4 - 8.95 × 10−4 Ω-cm. We were able to separate the roles of grain boundary and ionized impurity scatterings in modifying µITO as a function of NITO in the ITO films. Finally, using the transfer length method, we observed a contact resistivity of ∼3 mΩ-cm² from the ITO/Ag interface at the NITO of ∼4.08 × 1020 cm−3.

Ultrahigh Responsivity In2O3 UVA Photodetector through Modulation of Trimethylindium Flow Rate

Oxygen vacancies (Vo) can significantly degrade the electrical properties of indium oxide (In2O3) thin films, thus limiting their application in the field of ultraviolet detection. In this work, the Vo is effectively suppressed by adjusting the Trimethylindium (TMIn) flow rate (fTMIn). In addition, with the reduction of the fTMIn, the background carrier concentration and the roughness of the film decrease gradually. And a smooth In2O3 thin film with roughness of 0.44 nm is obtained when the fTMIn is 5 sccm. The MSM photodetectors (PDs) are constructed based on In2O3 thin films with different fTMIn to investigate the opto-electric characteristics of the films. The dark current of the PDs is significantly reduced by five orders from 100 mA to 0.28 μA with the reduction of the fTMIn from 50 sccm to 5 sccm. In addition, the photo response capacity of PDs is dramatically enhanced. The photo-to-dark current ratio (PDCR) increases from 0 to 2589. Finally, the PD with the fTMIn of 5 sccm possesses a record-high responsivity of 2.53 × 103 AW−1, a high detectivity of 5.43 × 107 Jones and a high EQE of 9383 × 100%. Our work provides an important reference for the fabrication of high-sensitivity UV PDs.

Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors.

In this study, a KrF excimer laser with a high-absorption coefficient in metal oxide films and a wavelength of 248 nm was selected for the post-processing of a film and metal oxide thin film transistor (MOTFT). Due to the poor negative bias illumination stress (NBIS) stability of indium gallium zinc oxide thin film transistor (IGZO-TFT) devices, terbium-doped Tb:In2O3 material was selected as the target of this study. The XPS test revealed the presence of both Tb3+ and Tb4+ ions in the Tb:In2O3 film. It was hypothesized that the peak of the laser thermal effect was reduced and the action time was prolonged by the f-f jump of Tb3+ ions and the C-T jump of Tb4+ ions during the laser treatment. Studies related to the treatment of Tb:In2O3 films with different laser energy densities have been carried out. It is shown that as the laser energy density increases, the film density increases, the thickness decreases, the carrier concentration increases, and the optical band gap widens. Terbium has a low electronegativity (1.1 eV) and a high Tb-O dissociation energy (707 kJ/mol), which brings about a large lattice distortion. The Tb:In2O3 films did not show significant crystallization even under laser energy density treatment of up to 250 mJ/cm2. Compared with pure In2O3-TFT, the doping of Tb ions effectively reduces the off-state current (1.16 × 10-11 A vs. 1.66 × 10-12 A), improves the switching current ratio (1.63 × 106 vs. 1.34 × 107) and improves the NBIS stability (ΔVON = -10.4 V vs. 6.4 V) and positive bias illumination stress (PBIS) stability (ΔVON = 8 V vs. 1.6 V).

Effect of sputtering pressure on the properties of large area IWO thin films deposited by direct current magnetron sputtering

Tungsten doped indium oxide (In2O3: W, IWO) thin films have been attracting increasing attention due to their excellent optoelectronic properties. Here, a series of IWO thin films were prepared using direct current (DC) magnetron sputtering method, by varying the sputtering pressure. Analysis revealed that the IWO films prepared under sputtering pressure of 0.4 Pa exhibited excellent optoelectronic performance, with low square resistance, resistivity, high carrier concentration and mobility. The resulting semi-transparent perovskite solar cells (ST-PSCs), with IWO fabricated under 0.4 Pa, yield a PCE of 15.71 % for the large area modules of 100 cm2 (active area 64.8 cm2).

Zirconium doped indium oxide thin films as transparent electrodes for photovoltaic applications

In this work we report on ultra-thin Zirconium doped In2O3 transparent conductive films grown at room temperature via RF-Magnetron co-sputtering. Samples from 15 nm to 90 nm thick, and low Zr atomic concentration (0.6–0.9 at.%), were annealed at T = 200 °C after the deposition. The phase-transition from amorphous to crystalline, confirmed by XRD measurements, leads to an improvement of both electrical and optical properties. The thinnest film (15 nm) shows electrical resistivity as low as 5 × 10−4 Ωcm, with carrier mobility of 20 cm2V−1s−1, and optical transmittance up to 80 % in visible and near-infrared range. IZrO electrode performances were tested through external quantum efficiency (EQE) measurements on a semi-finite Silicon Heterojunction bi-facial solar cell. The EQE values for 90 nm thick film are comparable to that of standard ITO when IZrO films are implemented as front electrodes. These results suggest that ultra-thin IZrO films may be successfully used to reduce costs and the amount of Indium used in Indium-based transparent conductive oxide layers for solar cells.

Molybdenum doped indium oxide thin films grown on mica substrates with high near-infrared transparency and electron mobility for flexible optoelectronic and spintronic applications

In the era of the artificial intelligence, flexible multifunctional films that combine optical transparency, electrical conductivity, and ferromagnetism are highly beneficial for many advanced applications. Herein, we fabricated a flexible magnetic transparent conductor molybdenum doped indium oxide (IMoO) thin film on a mica substrate using a pulsed laser deposition (PLD) technique. The valence states of Mo dopants were determined to be Mo4+ and Mo6+ by X-ray photoelectron spectroscopy (XPS) analysis. From the measured optical transmittance spectrum, average visible (Vis) and near-infrared (NIR) transmittance (Tave_Vis and Tave_NIR) values in IMoO film are calculated to be 85.9 % and 85.4 %, respectively. The IMoO film shows an electron mobility (μe) of around 113 cm2 V−1 s−1 and a sheet resistance (Rs) of 69 Ω. We illustrate the benefits of Mo doping, which leads to increased NIR transparency and μe compared to commercially available tin-doped indium oxide (ITO). On the other hand, the IMoO film shows clear magnetic hysteretic behaviors at room temperature, indicating the presence of ferromagnetism. The main origin of the ferromagnetism is presumably attributed to the Mo4+ ions with an electronic configuration of 4 d2. Bending cyclic tests reveal favourable mechanical durability and bending stability in the IMoO/mica films. Our systematic investigation demonstrates that IMoO film possesses a superior optoelectronic performance beyond ITO, Mn-doped indium oxide (IMnO), and Sn-Mn-codoped indium oxide (ITMnO), substantiating the potential of the IMoO/mica film as a high-performance transparent conductive magnetic material for flexible optoelectronic and spintronic applications.

Dependence of Positive Bias Stress Instability on Threshold Voltage and Its Origin in Solution-Processed Aluminum-Doped Indium Oxide Thin-Film Transistors.

The initial electrical characteristics and bias stabilities of thin-film transistors (TFTs) are vital factors regarding the practical use of electronic devices. In this study, the dependence of positive bias stress (PBS) instability on an initial threshold voltage (VTH) and its origin were analyzed by understanding the roles of slow and fast traps in solution-processed oxide TFTs. To control the initial VTH of oxide TFTs, the indium oxide (InOx) semiconductor was doped with aluminum (Al), which functioned as a carrier suppressor. The concentration of oxygen vacancies decreased as the Al doping concentration increased, causing a positive VTH shift in the InOx TFTs. The VTH shift (∆VTH) caused by PBS increased exponentially when VTH was increased, and a distinct tendency was observed as the gate bias stress increased due to a high vertical electric field in the oxide dielectric. In addition, the recovery behavior was analyzed to reveal the influence of fast and slow traps on ∆VTH by PBS. Results revealed that the effect of the slow trap increased as the VTH moved in the positive direction; this occured because the main electron trap location moved away from the interface as the Fermi level approached the conduction band minimum. Understanding the correlation between VTH and PBS instability can contribute to optimizing the fabrication of oxide TFT-based circuits for electronic applications.

High-performance ammonia gas sensor based on spray pyrolysis developed In2O3:La films

La doped indium oxide (In2O3:La) thin films were deposited on glass substrate by nebulizer spray pyrolysis by different La doping concentrations. The crystalline structure, morphology, optical and gas sensing properties of thin films were investigated. XRD diffractograms present cubic crystal structure of In2O3 films, with decreased crystallite size with the incorporation of La dopants. SEM analysis of thin film samples exhibits approximately cube-shaped morphology without any cracks of microstructures. The optical band gap magnitude shows shift in energy values in the range of 3.12–3.29 eV with increasing La concentrations. For all films, the photoluminescence spectra showed violet-blue emission peaks at around 420–480 nm. All of the developed films were tested for ammonia (NH3) gas detection at ambient temperature. In2O3:La 5% sensor had the highest gas response value of 1720%, a quicker response and recovery times of 48/12 s, respectively, suggesting the sample could be better suited for the application of NH3 gas sensor.

Visible-light absorption of indium oxide thin films via Bi3+ doping for visible-light-responsive photocatalysis

In2O3 is commonly used as a photocatalyst for hydrogen energy storage. However, it has the disadvantage of a large optical bandgap (3.7 eV), resulting in low absorption of visible light, which corresponds to 50 % of sunlight energy. Band engineering is an efficient method to add visible-light responsivity to wide-bandgap In2O3. In this study, the band engineering of In2O3 was performed by incorporating bismuth to obtain an intermediate band that could absorb visible light. Thin films of In2O3 doped with bismuth (IBO) were grown using mist chemical vapor deposition (CVD), and their optical properties were investigated. Transmittance measurements showed that the IBO thin film exhibited absorption in the visible light region of 400–700 nm, indicating that the introduction of bismuth created an intermediate band in the bandgap of In2O3. IBO thin films with platinum as a co-catalyst could almost completely degrade methylene blue under visible light (420 nm) irradiation for 72 h. Thus, the incorporation of bismuth into In2O3 via mist CVD and the strong absorption of visible light owing to its intermediate band were demonstrated. This study demonstrates that IBO thin films with large absorption in the visible-light region are promising materials for visible-light-responsive photocatalysts.

Low-temperature rapid preparation of high-performance indium oxide thin films and transistors based on solution technology

Indium oxide (In<sub>2</sub>O<sub>3</sub>) thin films and thin-film transistors (TFTs) based on the solution process are prepared by pulsed UV-assisted thermal annealing at a low temperature (200 ℃) for 5 min. The effects of pulsed UV-assisted thermal annealing on the surface morphology, chemical structure, and electrical properties of the In<sub>2</sub>O<sub>3</sub> thin films are investigated, and they are compared with those of conventional thermal annealing (300 ℃, 30 min). The experimental results show that the pulsed UV-assisted thermal annealing method can improve the quality of In<sub>2</sub>O<sub>3</sub> thin film and the performance of TFT in a short period. The results of atomic force microscopy and field emission scanning electron microscopy show that the surface of the In<sub>2</sub>O<sub>3</sub> film is denser and flatter than that of the conventional thermally annealed film, and X-ray photoelectron spectroscopy tests show that the pulsed UV-assisted thermal annealing process generates oxygen vacancies, which increases the carrier concentration and improves the electrical conductivity of the In<sub>2</sub>O<sub>3</sub> film. In addition, the effect of pulsed UV-assisted thermal annealing on the electrical characteristics of In<sub>2</sub>O<sub>3</sub> TFTs is investigated in a comparative way. The results show that the electrical characteristics of the device are significantly improved: the subthreshold swing decreases to 0.12 mV/dec, the threshold voltage is 7.4 V, the current switching ratio is as high as 1.29×10<sup>7</sup>, and the field effect mobility is enhanced to 1.27 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>. Therefore, pulsed UV-assisted thermal annealing is a simple and fast annealing method, which can rapidly improve the performances of In<sub>2</sub>O<sub>3</sub> thin film and TFTs, even under low-temperature conditions.

Unveiling growth mechanisms of PEALD In2O3 thin films with amide-based versus alkyl-based novel indium precursors

New indium precursors based on alkyl and amine ligands make a difference in the properties of indium oxide thin films.

Uniformity and Reliability of Enhancement-mode Polycrystalline Indium Oxide Thin Film Transistors formed by Solid-phase Crystallization

Uniformity and Reliability of Enhancement-mode Polycrystalline Indium Oxide Thin Film Transistors formed by Solid-phase Crystallization