Undoped Indium Oxide Research Articles

Study on aluminium oxide doping modification of indium oxide and thermoelectric properties

Traditional thermocouples face challenges in meeting the temperature measurement requirements of crucial aero-engine components, such as low interference, high temperature resistance, quick response, and in-situ measurement. The temperature measurement requirements mentioned above can be satisfied by thin film thermocouples, thanks to advancements in thin-film preparation technology. In this study, the indium oxide (In2O3) was calculated using first principle calculation both before and after doping. It was found that doping Aluminium oxide (Al2O3) can increase the Seebeck coefficient of In2O3. Solid-phase sintering was used to create aluminum oxide-doped In2O3 nanopowders, and thin film thermocouples were fabricated using screen printing. The thermoelectric characteristics of thin film thermocouples were studied to analyze the effects of different annealing procedures and doping concentrations. The optimal annealing process was determined to be at 1300 °C for 1 h, and the ideal doping ratio was found to be Al0.1In2O3.15. The indium oxide film doped with aluminum oxide exhibits a Seebeck coefficient that is 45.9% higher than that of the undoped indium oxide film. The thin film thermocouples underwent tests for impact and vibration resistance, laser pulse response, surface and cross-section morphology, X-ray diffraction, and thermoelectric output. It has been confirmed that doping indium oxide with aluminum oxide can increase a material's Seebeck coefficient. Additionally, a thin-film temperature sensor that has been prepared can be used in challenging conditions to meet the temperature measurement requirements of an aero engine.

Cerium-doped indium oxide nanosphere arrays with enhanced ethanol-sensing properties

Mesoporous gas-sensitive nanomaterials have attracted the attention of more and more researchers because of their excellent stability and selectivity. Herein, pure and cerium-doped indium oxide 3D nanosphere (26–19 nm in diameter) arrays were synthesized via nanocasting using mesoporous silica as hard templates. The content of the Ce dopant ions has been found critical to control the structure, optical properties, and gas-sensing activities of the materials. The Ce-doped indium oxide shows significantly improved gas-sensing properties as compared to undoped indium oxide. And the sensor fabricated from the 3 mol% Ce-doped In2O3 with mesoporous nanospheres exhibited excellent sensing properties to ethanol at the optimum temperature of 330 °C. The significantly improved sensing performances may be ascribed to the mesostructured morphology and the doping of Ce ion. Optimizing the performance of mesoporous gas-sensing materials through various channels still requires our continuous efforts.

Waveguiding behavior of VLS-grown one-dimensional Ga-doped In2O3 nanostructures

Highly crystalline undoped and Ga-doped indium oxide nanorods with square-shaped faceted morphology were fabricated through the vapor-liquid-solid process at moderate temperature. Effects of Ga incorporation on the growth rate, morphology, and crystallinity of the nanostructures were evaluated by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Defect structure and waveguiding behavior of the 1-D In2O3 nanostructures have been studied using microRaman and micro photoluminescence spectroscopies. The appearance of several resonant modes superposed over the broad room temperature micro-photoluminescence spectra of the nanostructures demonstrates their waveguiding behaviors. While the pristine or undoped In2O3 nanostructures of 20–150 nm widths revealed Fabry-Pérot resonance modes, the Ga-incorporated nanostructures of 20–100 nm width revealed whispering gallery modes due to their smaller widths. The quality factor (Q) of the resonators was estimated to be about 20.86 and 188.79 for the pristine and Ga-incorporated nanostructures, respectively, indicating a huge enhancement due to Ga incorporation. The increment in the Q factor on Ga incorporation in In2O3 nanorods opens up the possibility of their utilization for the development of new optical transmitters and resonators, and fabrication of nanoscopic lasing devices.

Localized Surface Plasmon Coupling between Mid-IR-Resonant ITO Nanocrystals.

Sn-doped indium oxide (ITO) nanocrystals (NC) provide tunable localized surface plasmon resonance in the mid-infrared. To evaluate the applicability of these n-doped plasmonic semiconductors in field-enhanced spectroscopies, it is necessary to assess how the low, free-electron density affects the E-field localization and plasmon coupling in NC films when compared to metal nanoparticles (NP). In this article, we investigate plasmon coupling between approximate 6 nm diameter ITO NC on the collective resonance and quantify the effect of the electromagnetic field enhancement on the absorbance signal of surface-attached ligands in NC films and monolayers with different ratios of doped and undoped indium oxide NC.

Sol Gel Dip Coated Yb and Tm Doped Indium Oxide Dye Sensitizrd Solar Cells

In2O3 thin films were deposited by the sol gel dip coating method adopting the following procedure. Clean ITO substrates were used for the deposition of the films. 10 ml of 0.33 M solution of Indium (III) nitrate was taken in a clean glass beaker. The solution was heated to 70˚C and the pH was brought to 9 by the addition of ammonia, then 1 gm of Acrylamide was added followed by the addition of 0.25 gm of N,N,bis methylene acrylamide. After 20 min, 5 mg ammonium persulphate initiator was added to this mixture. The solution became viscous. Cleaned microglass slides (2.5 cm x 7.5 cm) were immersed into the viscous solution and withdrawn at the rate of 1cm min-1. The film formed on the surface was dried in an air oven for about 15 min followed by annealing in air at different temperatures in the range of 350 - 500˚C for different durations in the range of 15 min to 90 min. Doping with Tm and Yb was done by adding 0.1 g of Yb(NO3)3 and 0.1 g of Tm(NO3)3 to the Indium nitrate solution before gelling. The doped and undoped films were dipped in N719 dye for 24 hours. a sandwich structure was formed by bonding the FTO substrate with dye coated In2O3 and a Pt counter electrode together through a hot-melt spacer, and a drop of electrolyte (0.60 M 1-butyl-3-methylimidazolium iodide (BMII), 0.03 M I2 was injected into the device through predrilled holes on the Pt counter electrode. DSSCs based on In2O3:Yb and In2O3:Tm were also fabricated via the same process. The XRD patterns of the In2O3, In2O3:Tm and In2O3:Yb. . All the patterns can be assigned to cubic phase standard card (JCPDS 06-0416) without any additional diffraction peaks. The UV–vis absorption spectra of the doped and undoped In2O3 exhibit the absorption peak of the pure In2O3 about 3.85 eV, which is consistent with the results published, and it icreases to 3.93 eV and 4.00 eV respectively as Tm and Yb are doped into In2O3. The J-V characteristics of the doped and undoped Indium oxide films indiacted that the Voc increased from 410 mV for undoped films increased to 530 mV and 630 mV for Tm and Yb doped films respectively. The Jsc increased from 2.45 mA cm-2 for the undoped films increased to 3.50 mA cm-2 and 4.25 mA cm-2 for Tm and Yb doping respectively.IPCE measurements indicated that for doped films the PCE was higher than that of undoped films. The fill factor of the films increased by doping with Tm and Yb. The larger Voc obtained with Yb doping can be explained on theb basis that the conduction band edge of Yb doped films is higher than that of undoped and Tm doped Indium oxide.

Structure and optical properties of vapor grown In<sub>2</sub>O<sub>3</sub>: Ga nano-/microcrystals

Octahedral shaped single crystalline undoped and Ga-doped indium oxide nano-and microcrystals were fabricated using vapor-solid growth process. Effects of Ga doping on the crystallinity, defect structure, and optical properties of the nano-/microstructures have been studied using scanning electron microscopy, microRaman spectroscopy, transmission electron microscopy and cathodoluminescence spectroscopy. It has been observed that incorporation of Ga does not affect the morphology of In2O3 structures due to its smaller ionic radius, and similar oxidation state as that of In. However, incorporation of Ga in high concentration (~3.31 atom %) causes lattice compression, reduces optical band gap and defect induced CL emissions of In2O3 nano-/microcrystals. The single crystalline Ga-doped, In2O3 nano-/microcrystals with low defect contents are promising for optoelectronic applications.

Effect of Li doping on the structural, optical and formaldehyde sensing properties of In2O3 thin films

Chemical spray pyrolysis technique is utilized to deposit undoped and Li-doped indium oxide thin films on cleaned glass substrates. The effect of Li doping on the structural, optical, electrical and formaldehyde sensing characteristics on In2O3 has been studied. All the thin film samples were characterized by X-ray diffraction for structural and UV–vis spectroscopy for optical analyses, respectively. The doping of Li into In2O3 reduces the value of the average crystallite size and the optical transmittance in the visible region. However, a blue shift is observed in the optical band gap in the Li-doped films. The value of the direct optical band gap is found to increase from 3.35eV in the undoped sample to 3.59eV in the 2at.% Li:In2O3 thin film. Further, the undoped and the Li-doped films have been tested for formaldehyde vapor to check their suitability to detect the presence of the same in air. We observed that the 2at.% Li:In2O3 film exhibits the highest sensitivity for formaldehyde at a low concentration of 60ppm and at an operating temperature of 300°C. The sensing mechanism of formaldehyde vapor has also been presented.

On the oxygen content in sputtering InOx film for transparent electronics

Transparent undoped semiconductor indium oxide films were deposited by using a long-throw rf magnetron sputtering at room temperature. It was found that the variation of oxygen content in sputtering gas has a strong influence on the microstructure and electrical properties of the films. The electrical resistivity varying from 3.5 × 10−2 to 4.7 × 104 Ω-cm for oxygen contents ranging from 0 to 50 % was obtained. The optical band gap decreases as the oxygen content increases, and the average visible transmittance of the indium oxide is ~85 %. To put into practice, the as-sputtered indium oxide was employed as a channel of thin film transistors on glass substrate with a channel length, 6 μm, and a channel width, 20 μm. Its saturation mobility, threshold voltage, and on/off ratio were obtained to be 9.4 V−1 s−1, 1.5 V, and 2.2 × 107. To approach a flexible device, a plastic substrate is employed to replace the rigid substrate, glass; and the relative parameters, saturation mobility, threshold voltage, and on/off ratio, are also measured to be 8.2 V−1 s−1, 1.8 V, and 1.4 × 106, respectively.

Epitaxial undoped indium oxide thin films: Structural and physical properties

Indium oxide thin films were grown by the pulsed electron beam deposition method on c-cut sapphire substrates at 10−2mbar oxygen pressure and temperature up to 500°C. Such conditions lead to the formation of dense, smooth and stoichiometric In2O3 films, with the cubic bixbyite structure. Epitaxial thin films were obtained at substrate temperatures as low as 200°C. Pole figure measurements indicate the existence of (111) oriented In2O3 crystallites with different in-plane symmetry, i.e. three-fold and six-fold symmetry. The origin of this effect may be related to the specificities of the growth method which can induce a large disorder in the oxygen network of In2O3, leading then to a six-fold symmetry in the (111) plane of the bixbyite structure. This temperature resistivity behaviour shows metallic conductivity at room temperature and a metal–semiconductor transition at low temperature for In2O3 films grown at 200°C, while the classical semiconductor behaviour was observed for the films grown at 400 and 500°C. A maximum mobility of 24.7cm2/Vs was measured at 200°C, and then it falls off with improving the crystalline quality of films. The optical transparency is high (>80%) in a spectral range from 500nm to 900nm.

D ferromagnetism in undoped n and p-type In2O3 films

Undoped indium oxide films with room temperature d0 ferromagnetism were prepared by radiofrequency magnetron sputtering with different O2/Ar flux ratio. The optical and magnetic properties changed non-monotonously as the oxygen flux increases. A conversion of conductivity from n-type to p-type was observed as the flux ratio reached 15:15. The concordant results in structural, electrical, optical, and magnetic properties suggest that single ionized oxygen and indium vacancies play crucial roles in mediating the ferromagnetism in n and p-type In2O3 films, respectively.

On the Role of Tin Doping in InO<SUB><I>x</I></SUB> Thin Films Deposited by Radio Frequency-Plasma Enhanced Reactive Thermal Evaporation

In view of the increasing need for larger-area display devices with improved image quality it becomes increasingly important to decrease resistivity while maintaining transparency in transparent conducting oxides (TCOs). Accomplishing the goal of increased conductivity and transparency will require a deeper understanding of the relationships between the structure and the electro-optical properties of these materials. In this work we study the role of tin doping in InOx thin films. Undoped indium oxide (InOx) and indium tin oxide (ITO) thin films were deposited at room temperature by radiofrequency plasma enhanced reactive thermal evaporation (rf-PERTE), a new technique recently developed in our laboratory using as evaporation source either In rods or a 90%In:10%Sn alloy, respectively. The two most important macroscopic properties-optical transparency and electrical resistivity-seem to be independent of the tin content in these deposition conditions. Results show that the films present a visible transmittance of the order of 82%, and an electrical resistivity of about 8 x 10(-4) omega x cm. Surface morphology characterization made by atomic force microscopy (AFM) showed that homogeneity of the films deposited from a 90%In:10%Sn alloy is enhanced (a film with small and compact grains is produced) and consequently a smooth surface with reduced roughness and with similar grain size and shape is obtained. Films deposited from pure In rods evaporation source show the presence of aggregates randomly distributed above a film tissue formed of thinner grains.

Deposition of undoped indium oxide thin films on stripe-patterned substrates by spray CVD

Undoped indium oxide (In 2O 3) films were deposited on stripe-patterned Si substrates by an original spray chemical vapor deposition (spray CVD) using ethanol solution of indium (III) chloride. The step coverage of the films increased as the deposition temperature decreased. The grooves with 0.18 μm openings were successfully deposited at 253 °C. The step coverage of undoped indium oxide films were a similar tendency though resistivity of that showed the tendency opposite to the ITO film. Deposition mechanism of the undoped indium oxide films on stripe-patterned Si substrates was similar to that of the ITO films. The lowest resistivity of the films was 4.1×10 −3 Ω cm for the 260 nm-thick film deposited at 280 °C. The resistivity increased at higher temperature.

Influence of the annealing temperature on the properties of undoped indium oxide thin films obtained by the sol–gel method

Undoped indium oxide thin films were deposited on glass slides by the sol–gel method, starting from a simple precursor solution. The effect of the annealing temperature on the electrical, optical and structural properties of the films was studied. The structural and optical characterization techniques used were X-ray diffraction and ultraviolet–visible spectroscopy. The electrical characterization was made by Hall effect, four probes method and photoconductivity decay measurements. The crystalline indium oxide was formed with a first annealing (in air) at 300 °C and it showed the type-bixbyite phase. A second annealing treatment in controlled atmosphere enhanced the crystalline quality of the films. The grain size increased with this second annealing, for the films previously annealed in air at temperature lower than 500 °C. All the films showed photoconductive effect when they were only subjected to the first annealing. This effect decreased when they were again annealed. The energy of the traps responsible for this effect was evaluated by considering a multi-exponential model. The highest conductivity value of 10 2 Ω cm, corresponded to the films with the first annealing at 300 °C and the second annealing at 500 °C. When the films were thermally treated under these conditions, the conductivity value neither changed in time, nor in the presence of light. The films were highly transparent and had a direct band gap value around 3.65 eV.

Influence of oxygen partial pressure on the properties of undoped InOx films deposited at room temperature by rf-PERTE

Transparent and conductive/semiconductive undoped indium oxide (InOx) thin films were deposited at room temperature. The deposition technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied between 3×10−2 and 1.3×10−1Pa. Undoped InOx films, 100nm thick, deposited at the oxygen partial pressure of 6×10−2Pa show a conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7eV and an electrical conductivity of about 1100 (Ωcm)−1. For oxygen pressures greater than 6×10−2Pa, semiconductive films are obtained, maintaining the visible transmittance. Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6×10−2Pa show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.

InOx semiconductor films deposited on glass substrates for transparent electronics

Transparent undoped semiconductor indium oxide films were deposited by radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium at low substrate temperature. It was experimentally verified that the variation of rf power density has a strong influence on the electrical and structural properties of the films. The thickness of the InOx films is of about 100nm. Results show that InOx films show an average visible transmittance of about 85% and energy gap of about 2.6eV. Structural and electrical conductivity measurements show that films are polycrystalline and there exists a linear variation of conductivity logarithm vs reciprocal of temperature. Electrical conductivity variation of 17.6 to 5.8×10−3(Ω cm)−1 for films produced at rf power densities ranging from 3.9 to 78.1mWcm−3 was obtained. This controllable semiconductor behavior can therefore satisfy the requirement of a particular application for these type of films.

Development of radio-frequency magnetron sputtered indium molybdenum oxide

Molybdenum-doped indium oxide (IMO), an n-type transparent conducting oxide, was deposited using radio-frequency magnetron sputtering. The effects of oxygen concentration in an argon ambient and substrate temperature on film properties were studied. Compared to undoped indium oxide (In2O3) films, IMO films demonstrated higher electron mobility and more than an order-of-magnitude higher carrier concentration. The highest conductivity IMO film demonstrated a mobility of 44 cm2 V−1 s−1 and a carrier concentration of 1.3×1020 cm−3. The properties of both In2O3 and IMO films were very sensitive to the oxygen concentration, but not to the substrate temperature. Average visible transmittance of In2O3 and IMO films were 86% and 80%, respectively. Both optical and x-ray photoelectron spectroscopy analyses indicate a possible second phase in IMO films deposited at lower (⩽1%) oxygen concentrations.

Preparation and Crystallization of Tin-doped and Undoped Amorphous Indium Oxide Films Deposited by Sputtering

Tin-doped and undoped amorphous indium oxide films were prepared by dc magnetron sputtering without substrate heating at relatively high total gas pressures and relatively large target-substrate distance. The structural and electrical properties of these films were investigated by X-ray diffraction and Hall-effect measurements. The amorphous tin-doped indium oxide (a-ITO) films were crystallized at a temperature about 30°C higher than that for amorphous indium oxide (a-IO) films.

Activation energy for the formation of oxygen vacancies in undoped nonstoichiometric indium oxide films

An analysis is made of the temperature dependence of the electrical conductivity of undoped nonstoichiometric indium oxide films. Activation energies are obtained for the formation of oxygen vacancies and for the mobility of quasifree carriers.

Doping-induced changes in the physical properties of In2O3:Sn films

Here we report studies carried out on heavily tin-doped and undoped indium oxide films. Structural, electronic transport and compositional properties of the sprayed films deposited with different doping levels of tin (0-110 at.% in solution), were investigated. X-ray diffraction, room-temperature Hall effect measurements, conductivity measurements at low temperatures and x-ray photoelectron spectroscopy were used for these studies. The films were polycrystalline and the preferred growth showed systematic changes with dopant incorporation from (400) to (222). The carrier mobility was very sensitive to these changes in orientation of preferred growth as well as the grain size. The high carrier concentration ( approximately 1020 cm-3) implied that the films belong to the class of degenerate semiconductors. Such a high carrier concentration was a result of increased non-stoichiometry and increased dopant incorporation. The conductivity measurements at low temperatures show that with increased Sn incorporation, electronic transport is governed by ionized impurity scattering and acoustic lattice scattering.

Properties of Low-Resistivity Undoped indium-Oxide Films Grown by Reactive Ion Plating and Electrochromic Tungsten-Oxide Films Grown by Electron-Beam Evaporation

AbstractThe use of gaseous discharge for ion plating and related techniques have been well known to improve coating properties in several ways. IN the arc-induced ion plating (AIIP), the ionization efficiency for the evaporants is so enhanced without any introduction of inert gases that the bias voltage for, and the temperature of the substrate are reduced in the preparation of the coatings. Highly transparent (> 90% transmission in the visible range) and highly conductive (resistivity ≅ 1.5 x 10-4 Ω cm) in-oxide films were deposited at a rate of 500 - 900 Å/min by aIIP of pure in in an O2 atmosphere of 10-4 Torr. Hall-effect measurement revealed that the observed low resistivity is due primarily to the excellent electron mobilty (≥ 70 cm2 / V sec) with carrier density up to 7 х 1020/cm3. Electrochromic WO3 films were also prepared and characterized.