Indium Oxide Films Research Articles

Realizing the Potential of RF-Sputtered Hydrogenated Fluorine-Doped Indium Oxide as an Electrode Material for Ultrathin SiOx/Poly-Si Passivating Contacts

In high-efficiency silicon solar cells featuring carrier-selective passivating contacts based on ultrathin SiOx/poly-Si, the appropriate implementation of transparent conductive oxide (TCO) layers is of vital importance. Considerable deterioration in passivation quality occurs for thin poly-Si-based devices owing to the sputtering damage during TCO deposition. Curing treatment at temperatures above 350 °C can recover such degradation, whereas the opto-electrical properties of the TCO are affected as well, and the carrier transport at the poly-Si/TCO contact is widely reported to degrade severely in such a procedure. Here, we propose straightforward approaches, post-deposition annealing at 400 °C in nitrogen, hydrogen, or air ambience, are proposed to tailor material properties of high-mobility hydrogenated fluorine-doped indium oxide (IFO:H) film. Structural, morphological, and opto-electrical properties of the IFO:H films are investigated as well as their inherent electron scattering and doping mechanisms. Hydrogen annealing treatment proves to be the most promising strategy. The resulting layer exhibits both optimal opto-electrical properties (carrier density = 1.5 × 1020 cm-3, electron mobility = 108 cm2 V-1 s-1, and resistivity = 3.9 × 10-4 ω cm) and remarkably low contact resistivities (∼20 mω cm2 for both n- and p-contacts) in poly-Si solar cells. Even though the presented cells are limited by the metallization step, the obtained IFO:H-base solar cell show an efficiency improvement from 20.1 to 20.6% after specific hydrogen treatment, demonstrating the potential of material manipulation and contact engineering strategy in high-efficiency photovoltaic devices endowed with TCOs.

Composition formula of transparent conductive tin doped indium oxide in terms of cluster plus glue atom model

Abstract As transparent electrode, the tin (Sn) doped indium oxide (In2O3) film has been widely used in the photo-electric and electric-photo conversion devices. While, the relation between carrier concentration and Sn doping content in Sn doped In2O3 (ITO) film hasn’t be revealed satisfactorily enough. In this article, the so-called ‘cluster plus glue atom’ model was first used to describe In2O3 and ITO. Based on the definition rule of cluster, the principal and unit cluster formula of In2O3 were [In–O6]In3 and ([In–O6]In3)-([In–O6]In3)6-([In–O6]In3), respectively. Then, with the lowest Sn doping content, the unit cluster formula and composition formula of ITO could be expressed as ([Sn–O6]In3)-([Sn–O6]In3) ([In–O6]In3)5-([Sn–O6]In3) and Sn3In29O48, respectively. The unit cluster of ITO showed Sn/In atom ratio of 10.34 at.%, which corresponded well with that of commercial ITO material (10.30 at.%). Based on ITO unit cluster, the theoretical optimal value of ITO electron carrier concentration could reach 2.9 × 1021 (/cm3). Actually, the experimental value of electron carrier concentration of ITO was lower than 1/3 of the theoretical optimal one. The difference between theoretical optimal value and experimental value of ITO electron carrier concentration was discussed based on the unit cluster formula of ITO. Finally, with the better understanding of ‘cluster plus glue atom’ model, the new type of transparent conductive oxide materials could be designed and applied in future.

Dip Coated Indium Oxide Films and Their Optical Constants

Metal oxide play very important role in the field of semiconductors. Metals have high reflectivity for the light radiation in the range of infrared and visible range and low reflectivity in the ultraviolet and higher frequency range. Indium oxide thin films were successfully deposited by the sol gel dip coating method. The envelope method was used to evaluate the optical parameters and thickness. Resistivity, mobility and carrier concentration were obtained from Hall measurements. The dispersion energy was obtained from the single effective oscillator model. The energy band gap values estimated from Tauc’s plot and the static refractive index estimated from the Cauchy’s curve fitting agree well with single effective oscillator model. Optical characteristics of materials are determined by the interaction of the electromagnetic radiation with the valence electron of the materials which lies within or near visible range of electromagnetic spectrum. The other optical parameters like optical conductivity and the dielectric constants were also evaluated.

Determination of Electrodynamic Parameters of In2O3 thin Films by Terahertz and Infrared Spectroscopy

Indium oxide is a transparent semiconductor widely used in optical-electronic systems of the visible and near infrared range, but insufficiently studied in the terahertz frequency range. In this study, the dielectric response function of indium oxide thin films on glass substrates was investigated by terahertz and infrared spectroscopy techniques to determine the effect of free carriers on the optical characteristics of films. The experimental results were analyzed applying multiparametric dispersion model of Drude–Lorentz. The basic electrodynamic parameters of In2O3 films are determined. Model transmission and conductivity spectra for films of different thickness are calculated. The possibility of using thin films of indium oxide as a transparent conductive layer in terahertz optoelectronics devices is shown.

Effect of crystalline structure on optical and electrical properties of IWOH films fabricated by low-damage reactive plasma deposition at room temperature

Tungsten and water co-doped indium oxide (IWOH) films were deposited via a low-damage reactive plasma deposition method at room temperature followed by air atmosphere annealing. The structural, electrical, and optical properties of IWOH films with different water flow rates (F H2O ) were systematically investigated before and after annealing. Despite the lower mobility (43.7 cm 2 /V) of IWOH films with high water flow rate (H-F H2O , F H2O ≥ 1.5 sccm) in the as-deposited state, it has increased to 65.2 cm 2 /V, which surpassed IWOH films with low water flow rate (L-F H2O , F H2O < 1.5 sccm) after annealing. Meanwhile, a significant increase in average optical transmittance from 80.9% to 88.8% and from 92.2% to 95.2% in the short wavelength of visible (350–500 nm) and near-infrared region (800–2500 nm), respectively, was obtained for H-F H2O films after annealing. The variation of the optical and electrical properties for IWOH films with different F H2O was attributed to the crystalline structure with a larger crystallite size and lower density of grain boundary. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy analysis revealed that high water flow rate impeded crystallization of IWOH films during reactive plasma deposition, leading to an amorphous structure in the as-deposited state. After annealing, however, the H-F H2O films crystallized and exhibited larger grains than both tungsten-doped indium oxide (IWO) and L-F H2O films. The modified crystalline properties of IWOH films with larger grains hence reducing grain-boundary scattering, which was realized by H-F H2O and annealing treatment, gave rise to enhanced electrical properties without deteriorating optical properties. • Hydrogen-doped indium tungsten oxide was fabricated by reactive plasma deposition at room temperature. • Structural, optical and electrical properties were studied as a function of water flow rate. • Proper water flow rate can enhance the crystalline quality with fewer grain boundary scattering. • The modified crystalline properties with reduced grain boundary led to enhanced mobility.

Low frequency noise characteristics of resistor- and Si MOSFET-type gas sensors fabricated on the same Si wafer with In2O3 sensing layer

By analyzing the Low Frequency Noise (LFN) characteristics of the resistor-type and the Si metal oxide semiconductor Field Effect Transistor (FET)-type gas sensors fabricated on the same wafer, the intrinsic device noise and the additional noise generated from the gas reaction are systemically examined. Sensing material, n-type Indium-Oxide (In2O3) film, is deposited using the radio frequency magnetron sputtering method. Unlike the FET-type gas sensor, the LFN characteristics of the resistor-type gas sensor are affected by the deposition condition of the sensing material. It is shown that the FET-type sensor has at least 10 times less LFN power than the resistor-type gas sensor despite its smaller size. Gas to Air Noise Ratio (GANR) is introduced as a new figure of merit to evaluate and compare the LFN characteristics during the gas reaction in both resistor- and FET-type gas sensors with the sensing layer prepared by different process conditions. The GANRs of the resistor-type sensors range from ∼2 to 4, which demonstrates that the reaction between the gas molecules and the sensing material generates a fluctuation that exceeds the intrinsic noise of devices. However, the FET-type gas sensors have a constant value of GANR (∼1) regardless of the operation region, showing that the FET-type gas sensors have better performance in terms of noise.

Electron glass effects in amorphous NbSi films

We report on non equilibrium field effect in insulating amorphous NbSi thin films having different Nb contents and thicknesses. The hallmark of an electron glass, namely the logarithmic growth of a memory dip in conductance versus gate voltage curves, is observed in all the films after a cooling from room temperature to 4.2~K. A very rich phenomenology is demonstrated. While the memory dip width is found to strongly vary with the film parameters, as was also observed in amorphous indium oxide films, screening lengths and temperature dependence of the dynamics are closer to what is observed in granular Al films. Our results demonstrate that the differentiation between continuous and discontinuous systems is not relevant to understand the discrepancies reported between various systems in the electron glass features. We suggest instead that they are not of fundamental nature and stem from differences in the protocols used and in the electrical inhomogeneity length scales within each material.

Grain Structure and Electrical Properties of Transparent Indium Oxide Thin Films Prepared by RF Magnetron Sputtering

Transparent conductive films of indium oxide (In2O3) are deposited on a glass substrate by RF magnetron sputtering and their electrical properties are investigated in relation to their microstructure. Sputtering deposition was carried out with variations of normalized substrate temperature (Ts/Tm where Tm is the melting temperature) and argon partial pressure (PAr). At a very low substrate temperature (Ts/Tm &lt; 0.1), the columnar grains with voided grain boundaries are observed in the In2O3 films, which are attributed to the low surface mobility and atomic shadowing effect. With an increase in the substrate temperature, tight grain boundaries are formed between the growing columnar grains. At high temperature (0.3 &lt; Ts/Tm &lt; 0.5), the grain surface is faceted, which is due to the high surface mobility of the sputtered atoms, and development of preferred orientation with grain growth is promoted. The growing morphology is also dependent on the argon partial pressure. At low PAr deposition, an inclined fibrous grain oriented to the target direction and a smooth surface structure is developed. As the PAr increases, a dome-shaped surface structure and columnar grains normal to the substrate are developed due to the scattering effect of the sputtered atoms. The growing morphology with substrate temperature and argon pressure coincides with the Thornton's Structure Zone Model (SZM). The lowest electrical resistivity (2.1×10-2 Ωcm) is observed in the In2O3 films with tight grain boundaries and faceted grains, which corresponds to zone II region of the SZM.

Optical Property Change of Silver Nanowire Thin Films in Laser Patterning Process

Silver nanowire thin films are attractive materials for flexible electrodes as an alternative for conventional tin-doped indium oxide films. An appropriate patterning process is required to apply nanowire-based transparent electrodes into the optoelectronic devices. In this paper, we report the optical property change in silver nanowire transparent electrodes during laser ablation process. We discovered that, when silver nanowires were patterned by nanosecond pulsed lasers at infrared wavelength, their optical properties were changed. The change of optical properties was caused by nanoresidues remaining on the surface. It was analyzed that the color and transparency of thin films were changed because the residual nanoparticles absorbed the visible light wavelengths where silver nanoparticles possess their peak values in the absorption spectra. The nanoparticles were derived from insufficient vaporization of silver nanowires during infrared laser ablation. In the case of using an excimer laser for patterning, the nanoparticles were not left more on the surface due to complete removal of silver nanowires, since silver has higher absorption coefficient at the wavelength of excimer laser. As a result, high-quality patterning of silver nanowire thin films could be obtained without any deterioration of optical properties in transparent electrodes.

Ultrathin, highly flexible and optically transparent terahertz polarizer based on transparent conducting oxide

Multifunctional terahertz devices hold great promise for terahertz (THz) optical systems. Here, we present an ultrathin, highly flexible and optically transparent terahertz polarizer based on tin-doped indium oxide (ITO) and flexible conformal films of polyethylene terephthalate. The flexible optical transparent polarizer (FOTP) was theoretically investigated and experimentally characterized by UV–vis spectrophotometry and THz time-domain system. In the FOTP, THz conductivity of ITO films is mainly dominated by DC conductivity. The FOTP reveals a high optical transmittance of more than 60% in the visible region, a high extinction ratio of about 20 dB in the 0.1 THz–2.5 THz and a low insertion loss below 2 dB in the 0.1 THz–1.4 THz. The proposed FOTP can significantly improve the overall performance of THz optical systems and be easily fabricated by commercial display techniques. Our concept opens up a new window for highly flexible and optically transparent THz devices.

Role of Si Incorporation on the Transparent Conducting Properties of In2O3 Thin Films

Thin films of indium oxide (In2O3) incorporated with Si ion impurities were prepared on glass substrates by a vacuum evaporation technique. The influence of the Si inclusion on the structural and optical properties of the host In2O3 films was analytically studied by the Rietveld refinement method. It was observed that the insertion of Si ion-species into In2O3 lattice did not change its bixbyite phase. However, a gradual deterioration of crystalline structure with increasing of Si inclusion in the films sample was observed. The optical measurements revealed that the band gap of host In2O3 films blue-shifted by the inclusion of Si ions, which was ascribed to the Moss-Burstein effect. The transparent conducting properties of the films (conductivity, carrier mobility and concentration) were extracted from optical measurements, and compared with the known conduction parameters measured by a direct electrical method. The electrical conductivity, carrier concentration and optical transparency of host In2O3 films were improved with Si incorporation for concentrations less than ∼ 16 at.%. However, Si-incorporation decreased the carrier mobility. For Si inclusion of ∼ 16 at.%, In2O3:Si film shows a resistivity of 3.73 × 10−3 Ω cm and an optical transparency of ∼ 90%, which are acceptable values for the fabrication of different types of photovoltaics.

MoO&lt;SUB align="right"&gt;3:In&lt;SUB align="right"&gt;2O&lt;SUB align="right"&gt;3 binary oxide thin films as CO gas sensor

The aim of the study was to understand gas sensing properties of thin films of molybdenum trioxide and indium oxide (MoO3-In2O3) indifferent normality proportions. Thin films were prepared by spray pyrolysis technique on glass substrates at 400°C. The films were characterised using X-ray diffraction, scanning electron microscope and energy dispersive analysis by X-ray spectra. The electrical and gas sensing properties of the films were studied using static gas sensing apparatus. The resistivity of films increased by adding MoO3 as the dopant in In2O3. The maximum resistivity of film was found 1.75 × 104 Ωm for 0.3N (MoO3) and 0.1N (In2O3) binary oxide films. The films were tested against five different target gases. The composition ratio 0.3N:0.1N films showed the 70.50% sensitivity for 300 ppm CO gas at 150°C. The response time (15s) and recovery time (25s) was found to be quick.

Research progress of tin oxide-based thin films and thin-film transistors prepared by sol-gel method

Transparent conductive oxide (TCO) films and transparent oxide semiconductor (TOS) films have been widely adopted in solar cells, flat panel displays, smart windows, and transparent flexible electronic devices due to their advantages of high transparency and good conductivity and so on. Most of TCO and TOS films are mainly derived from indium oxide, zinc oxide and tin oxide. Among these materials, the In element is toxic, rare and expensive for indium oxide film, which will cause environmental pollution; zinc oxide film is sensitive to acid or alkali etchants, resulting in a poor formation of film patterning; tin oxide film is not only non-toxic, eco-friendly, and cheap but also has good electrical properties and strong chemical stability. Thus, tin oxide has a great potential for developing the TCO and TOS films. At present, the film is prepared mainly by the vacuum deposition technique. The drawbacks of this technique are complex and expensive equipment system, high energy consumption, complicated process and high-cost production. However, compared with the vacuum deposition technique, the sol-gel method has attracted extensive attention because of its virtues such as simple process and low cost. In this paper, we review the development status and trend of TCO and TOS films. First, the structural characteristics, conductive mechanism, element doping theory and carrier scattering mechanism of tin oxide thin films are introduced. Then the principle of sol-gel method and correlative film fabrication techniques are illustrated. Subsequently, the application and development of tin oxide-based thin films prepared by sol-gel method in n-type transparent conductive films, thin-film transistors and p-type semiconductor films in recent years are described. Finally, current problems and future research directions are also pointed out.

Impact of rough substrates on hydrogen-doped indium oxides for the application in CIGS devices

Indium oxide based transparent conductive oxides (TCOs) are promising contact layers in solar cells due to their outstanding electrical and optical properties. However, when applied in Cu(In,Ga)Se2 or Si-hetero-junction solar cells the specific roughness of the material beneath can affect the growth and the properties of the TCO. We investigated the electrical properties of hydrogen doped and hydrogen-tungsten co-doped indium oxides grown on rough Cu(In,Ga)Se2 samples as well as on textured and planar glass. At sharp ridges and V-shaped valleys crack-shaped voids form inside the indium oxide films, which limit the effective electron mobility of the In2O3:H and In2O3:H,W thin films. This was found for films deposited by magnetron sputtering and reactive plasma deposition at several deposition parameters, before as well as after annealing and solid phase crystallization. This suggests universal behavior that will have a wide impact on solar cell devices.

High-Mobility Hydrogenated Fluorine-Doped Indium Oxide Film for Passivating Contacts c-Si Solar Cells.

Broadband transparent conductive oxide layers with high electron mobility (μe) are essential to further enhance crystalline silicon (c-Si) solar cell performances. Although metallic cation-doped In2O3 thin films with high μe (>60 cm2 V–1 s–1) have been extensively investigated, the research regarding anion doping is still under development. In particular, fluorine-doped indium oxide (IFO) shows promising optoelectrical properties; however, they have not been tested on c-Si solar cells with passivating contacts. Here, we investigate the properties of hydrogenated IFO (IFO:H) films processed at low substrate temperature and power density by varying the water vapor pressure during deposition. The optimized IFO:H shows a remarkably high μe of 87 cm2 V–1 s–1, a carrier density of 1.2 × 1020 cm–3, and resistivity of 6.2 × 10–4 Ω cm. Then, we analyzed the compositional, structural, and optoelectrical properties of the optimal IFO:H film. The high quality of the layer was confirmed by the low Urbach energy of 197 meV, compared to 444 meV obtained on the reference indium tin oxide. We implemented IFO:H into different front/back-contacted solar cells with passivating contacts processed at high and low temperatures, obtaining a significant short-circuit current gain of 1.53 mA cm–2. The best solar cell shows a conversion efficiency of 21.1%.

Jet nebuliser spray pyrolysed indium oxide and nickel doped indium oxide thin films for photodiode application

Indium oxide thin films at different substrate temperatures (250−450 °C) and nickel doped indium oxide films with various doping concentration of 10 and 15 wt% were coated (at 400 °C) using jet nebulizer spray pyrolysis technique confirmed the cubic phase of the films from X-ray diffraction analysis. The micro-strain effects were also verified by Williamson-Hall method. Field emission scanning electron microscopy (FE-SEM) confirmed temperature dependence in the formation of octahedron layered geometry. The influence of temperature on surface irregularity and its effect on band gap shift confirmed using optical characterization was attributed to Burstein-Moss shift. The influence on doping was reinforced with the emission peak shift of photoluminescence spectra in ultra violet, violet and blue regions (394, 421 and 467 nm). Based on confirmations from these characterizations, n-In2O3/p-Si junction diodes were fabricated for as prepared In2O3 and 10 and 15 wt% concentrations nickel doped In2O3 at 400 °C. P-N junction diodes fabricated and analyzed showed high sensitivity for 15 wt% nickel doped indium oxide under illumination condition. On account of this 15 wt% nickel doped junction diode is a good candidate for optoelectronic devices.

Conducting indium oxide films on plastic substrates by plasma enhanced reactive thermal evaporation

This work reports on low temperature deposition of conducting indium oxide films by a radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE) technique. The films were deposited on polyethylene terephthalate (PET) without intentional heating of the substrate and at elevated temperatures up to 150 °C. The material stoichiometry was accurately controlled by adjusting deposition conditions including the oxygen flow, process pressure, pumping speed, and RF-power. Besides, fine turning of the critical deposition parameters during the deposition was implemented by measuring the variation of film conductance in-situ. The film morphology was analyzed by scanning electron microscopy. Hall effect measurements were also performed to determine the relation between the deposition conditions and the electrical properties of the films. A resistivity of 4 × 10−4 Ω-cm was reached under optimized deposition conditions. A 250 nm-thick coating with 16 Ω/sq sheet resistance shows an 82% peak value of transmittance in the visible spectral range.

Structural Dynamics in Thermal Treatment of Amorphous Indium Oxide Films

Thermal treatment of amorphous indium oxide (InxO) films is used in various basic studies as a means of tuning the disorder perceived by the electronic system. In this process, the resistance of a given sample decreases, whereas its amorphous structure and chemical composition is preserved. The main effect of the process is an increase in the system density, which, in turn, leads to improved interatomic overlap manifested as improved conductivity. A similar effect has been observed in studies of other amorphous systems that were subjected to pressure. Herein, the Raman spectra of amorphous InxO change in response to thermal treatment in a similar way as in pressure experiments performed on other disordered and amorphous systems. A study of how thermal treatment changes the system dynamics is presented by monitoring the resistance versus time of InxO films following various stages of thermal treatment. The time dependence of the sample resistance fits the stretched exponential law with parameters that change systematically with repeated thermal treatment cycles. The implications of these results to slow dynamics phenomena that are governed by the Kohlrausch's law are discussed.

Electrical conduction in gold nanoparticles embedded indium oxide films: a crossover from metallic to insulating behavior

Electrical conductivity of indium oxide and gold nanoparticles incorporated indium oxide films grown by dc sputtering have been studied in the temperature range 1.5 to 300 K. Films with 0, 6 and 12% gold nanoparticle volume fraction exhibit metallic nature in the temperature interval 1.5 to 20 K, with conduction being governed by electron–electron interaction. Films with 20% gold nanoparticle volume fraction showed insulating nature and the conduction was governed by variable range hopping mechanism in the temperature range 1.5 to 50 K. Furthermore, a crossover from Efros–Shklovskii to Mott type was observed around 15 K. The transition from metallic to insulating nature in spite of the larger gold nanoparticle volume fraction is attributed to the inhibition of oxygen vacancies by Au species during film growth. At higher temperatures, all films exhibit activated conduction.

Enhanced Nitrogen Dioxide Gas-Sensing Performance Using Tantalum Pentoxide-Alloyed Indium Oxide Sensing Membrane

In this paper, various tantalum pentoxide-alloyed indium oxide (Ta:In2O3) films were deposited on quartz substrates as the sensing membranes of nitrogen dioxide (NO2) gas sensors using a radio-frequency (RF) magnetron co-sputte-ring system. Using an energy-dispersive spectrometer (EDS), the Ta content in the deposited Ta:In2O3 films was 0, 1.28, 2.33, and 2.98 at.% corresponded to the RF power of 0, 30.0, 37.5, and 45.0 W applied to the tantalum pentoxide (Ta2O5) target, respectively. The grain size of the Ta:In2O3 films calculated from the X-ray diffraction (XRD) results was reduced from 9.9 to 7.6 nm as the Ta content of the Ta:In2O3 films increased from 0 to 2.98 at.%. The associated electron concentration increased from $1.9\times 10^{16}$ cm $^{-3}$ to $1.0\times 10^{18}$ cm $^{-3}$ by increasing the Ta content from 0 to 2.33 at.%. Compared with the indium oxide (In2O3) gas sensors, since the Ta:In2O3 sensing membrane with the Ta content of 2.33 at.% had the lowest activation energy of 0.39 eV, its responsivity was enhanced from 29.8 to 64.5 and the operation temperature was decreased from 150 °C to 120 °C under a NO2 concentration of 100 ppm. Under a NO2 concentration of 100 ppm at an operation temperature of 120 °C, the associated response time and recovery time of the Ta:In2O3 gas sensor with a Ta content of 2.33 at.% were improved to 59 and 339 s, respectively.