Sn-doped In2O3 Films Research Articles

Highly flexible and transparent amorphous indium doped tin oxide on bio-compatible polymers for transparent wearable sensors

Highly transparent and flexible amorphous Sn-doped In2O3 (a-ITO) films deposited on flexible and bio-compatible cyclic olefin polymer (COP) substrate using a direct-current magnetron sputtering at room temperature were used as flexible and transparent electrodes for transparent wearable sensors. The figure of merits (FoM) value was calculated to determine the optimal sputtering process for the a-ITO electrodes by varying the direct current power, working pressure, oxygen flow rate, and a-ITO thickness. The optimized a-ITO/COP with a high FoM value of 8.9 exhibited a low sheet resistance of 36 Ohm/square, average transmittances of 89.5 % in the visible wavelength region, and a small critical bending radius of 7 mm, which are acceptable transparent electrodes for fabrication of wearable and transparent wearable sensors. To demonstrate the feasibility of the a-ITO/COP substrate as a promising wearable sensor, we examined the performance of wearable temperature sensors, wearable heaters, and wearable glucose sensors. The successful operation of a-ITO/COP-based temperature sensors with high sensitivity, transparent heaters with a saturation temperature of 87.8 °C at 6 V, and glucose sensors with high sensitivity indicates that a-ITO/COP is a promising bio-compatible electrode for next-generation wearable bionic electronics.

Insights into the properties and possible bonding states of radiofrequency-magnetron-sputtered indium tin oxide thin films acquired using ultraviolet–visible spectroscopy data for cost-effective material characterization

Indium tin oxide (Sn-doped In2O3) is an optical material that is widely utilized in designing modern optoelectronic devices. To demonstrate the efficiency of ultraviolet–visible spectroscopy as a primary analysis tool for thin-film characterization, Sn-doped In2O3 films were deposited under untreated and annealed conditions. The optical parameters of these films were determined based on the transmission–reflection spectra recorded by an ultraviolet–visible spectroscopy laboratory setup. Through four-point probing, energy dispersive spectroscopy, and contact angle measurements, the electronic-band structures and chemical bonding states of the thin films were estimated. The transmission spectra confirmed that the post-annealing treatment promoted film homogeneity. Deeper insights into the optical parameters revealed that annealing encouraged Sn atom incorporation into the film structure and better stable phase formation. The incorporation of Sn atoms resulted in the substitution of Sn4+ into the In3+ sites of the In2O3 lattice and formation of the SnO phase. Notably, our evaluation of the film properties based on data acquired from ultraviolet–visible spectroscopy revealed good consistency with the data acquired from Hall-effect, X-ray diffractometry, and X-ray photoelectron spectroscopy investigations.

The Real-Time Monitoring of the Laser-Induced Functionalization of Transparent Conductive Oxide Films.

Laser-induced functionalization using excimer laser irradiation has been widely applied to transparent conductive oxide films. However, exploring suitable irradiation conditions is time-consuming and cost-ineffective as there are numerous routine film fabrication and analytical processes. Thus, we herein explored a real-time monitoring technique of the laser-induced functionalization of transparent conductive oxide films. We developed two types of monitoring apparatus, electrical and optical, and applied them to magnetron-sputtered, Sn-doped In2O3 films grown on glass substrates and hydrogen-doped In2O3 films on glass or plastic substrates using a picosecond Nd:YAG pulsed laser. Both techniques could monitor the functionalization from a change in the properties of the films on glass substrates via laser irradiation, but electrical measurement was unsuitable for the plastic samples because of a laser-induced degradation of the underlying plastic substrate, which harmed proper electrical contact. Instead, we proposed that the optical properties in the near-infrared region are more suitable for monitoring. The changes in the optical properties were successfully detected visually in real-time by using an InGaAs near-infrared camera.

Over 130 cm2/Vs Hall mobility of flexible transparent conductive In2O3 films by excimer-laser solid-phase crystallization

Flexible transparent electrodes on flexible plastic sheets are in significant demand for use in flexible perovskite solar cells (f-PSCs). However, the combination of the broadband high optical transparency and low electrical resistivity required for the tandemization of f-PSCs sets a stringent requirement on flexible transparent electrodes that are based on traditional Sn-doped In2O3 (ITO) films, owing to the high free-carrier concentration needed to reduce the electrical resistivity. Herein, we used excimer laser irradiation to achieve a Ce and H codoped In2O3 (ICO:H) film on flexible polyethylene terephthalate (PET) that had ultrahigh electron mobility of 133 cm2/Vs, which is the highest among those reported for flexible transparent electrodes, and low sheet resistance of 14.2 Ω/□, which is approximately three times lower than the 40 Ω/□ sheet resistance of commercially available ITO/PET. Furthermore, compared to ITO, this ICO:H film had higher infrared transparency. These nontrivial performances were achieved by an optimized excimer-laser solid-phase crystallization process guided by the correlation between laser pulse counts and the volume fractions of the amorphous and crystalline phases in the films. These high performances resolved the problems faced by ITO films, thus facilitating the performance of flexible solar cells and optoelectronic devices.

Electrical and optical properties of (In1-xSnx)2O3(1+δ) films (0.03 ≤ x ≤ 0.40, δ ≈ 0.28) grown on Si substrates using co-sputtering of In2O3 and SnO2

Sn-doped In2O3 (ITO) films are in high demand for use as transparent electrodes in optoelectronic devices. Technological developments have improved the quality of ITO films, and a detailed investigation of their properties is desired. Therefore, we investigated the composition dependence of the electrical and optical properties of (In1-xSnx)2O3(1+δ) films (with 0.03 ≤ x ≤ 0.40 and δ ≈ 0.28) films grown on Si and glass substrates utilizing the co-sputtering of In2O3 and SnO2 targets. Using X-ray diffraction, we found that the In2O3-like (222) phase was the dominant phase for x = 0.03. Further, the In2Sn2O7+x (400) phase became the dominant phase as the Sn concentration increased. This work demonstrates that ITO films exhibit excellent transmittance properties (T ≈ 88.3%) in the visible range as well as very low resistivities (ρ ≈ 2 × 10−4 Ω cm), regardless of the Sn composition. However, ITO films with Sn = 0.11, the commercially used composition, exhibited the lowest transmittance in the near-infrared range, 73.7%, whereas other ITO films showed large transmittances in the near-infrared range: T = 90.9% at x = 0.03 and T = 85.7% at x = 0.40.

High-Performance Indium-Tin Oxide (ITO) Electrode Enabled by a Counteranion-Free Metal-Polymer Complex.

Although multicomponent inorganic thin films (metal-oxides, -carbides, -nitrides, and -chalcogenides) have been synthesized by polymer-assisted deposition (PAD), synthesis of high-performance transparent conducting oxides (TCOs) has been rarely reported. TCO requires (i) removal of impurities, (ii) high-density oxide film, (iii) homogeneity in crystal structures and film morphology, and (iv) controllable elemental doping. This study performs a systematic investigation on preparation of stable multicomponent metal-polymer complex solutions by removing the counteranions in the solution. This study also proposes accurate acid-base titration for each metal species in order to minimize the amount of PEI, thus maximizing the density of the film. As a representative TCO, Sn-doped In2O3 (ITO) films have been achieved. The ITO film has an excellent sheet resistance (24.5 Ω/sq) at 93% optical transparency, with a figure of merit of 2.1 × 10-2 Ω-1, which is comparable to the best.

Toward flexible X-tronics: Transparent conductors with enhanced room-temperature ferromagnetism using Sn–Mn-codoped In2O3/mica thin films

Herein, flexible transparent conductors (TCs) with enhanced room-temperature ferromagnetism were fabricated via growing an Sn–Mn-codoped In2O3 (ITMO) film on a flexible mica substrate. The ITMO/mica film shows an average transmittance (Ta) of 81.9% in the visible region and a sheet resistance (Rs) of 58 Ω, which are comparable to those of the flexible Sn-doped In2O3 (ITO) and Mn-doped In2O3 (IMO) films in the previous reports. Moreover, the ITMO/mica film exhibits a room-temperature ferromagnetism with a saturation magnetization (Ms) of 29.1 emu/cc and a coercive field (Hc) of 430 Oe. The ferromagnetism in ITMO/mica film is much stronger than that in the previously reported IMO/mica films. The charge transport measurements in conjunction with bending tests indicate that the ITMO/mica film possesses large critical bending strains (ϵcr) and thus a robust mechanical durability. The optical and magnetic properties of the ITMO/mica film are also well maintained during the bending cyclic tests. The demonstration of the flexible multifunctional ITMO/mica films with remarkable performance in various aspects paves a route toward future flexible X-tronics.

Stable Sn-doped In2O3 films coated on Al2O3 for infrared transparent and electromagnetic shielding conductors

The transparency of most electromagnetic shielding conductors is limited to the visible regime. Here, we demonstrate the high infrared transmittance (>50% at 4-μm-wavelength), low sheet resistance (<200 Ω □−1 at room temperature), and high shielding effectiveness (∼16.2 dB at 10 GHz for the X-band) of 20–90-nm-thick Sn-doped In2O3 films deposited on an (0001)-oriented Al2O3 substrate. The phase persists even at 700 °C in air. Thus, multifunctional Sn-doped In2O3 films on Al2O3 substrates will advance technology in the areas of military applications, invisible circuitry, smart windows, infrared sensors, and transparent solar cells working in extreme environment.

Quantum magnetoconductivity characterization of interface disorder in indium-tin-oxide films on fused silica

Disorder arising from random locations of charged donors and acceptors introduces localization and diffusive motion that can lead to constructive electron interference and positive magnetoconductivity. At very low temperatures, 3D theory predicts that the magnetoconductivity is independent of temperature or material properties, as verified for many combinations of thin-films and substrates. Here, we find that this prediction is apparently violated if the film thickness d is less than about 300 nm. To investigate the origin of this apparent violation, the magnetoconductivity was measured at temperatures T = 15 – 150 K in ten, Sn-doped In2O3 films with d = 13 – 292 nm, grown by pulsed laser deposition on fused silica. We observe a very strong thickness dependence which we explain by introducing a theory that postulates a second source of disorder, namely, non-uniform interface-induced defects whose number decreases exponentially with the interface distance. This theory obeys the 3D limit for the thickest samples and yields a natural figure of merit for interface disorder. It can be applied to any degenerate semiconductor film on any semi-insulating substrate.

Origin of simultaneous enhancement of work function and carrier concentration in In2O3 films by excimer-laser irradiation

Excimer laser irradiation (ELI) has recently been revealed to simultaneously increase the work function (ϕ) and carrier concentration (N) in doped In2O3 films, suggesting a potential benefit in fabricating transparent conducting oxides (TCOs) for organic light emitting diodes (OLEDs). However, the phenomenon apparently contradicts with a basic physical argument: the Fermi (EF)-to-vacuum-level separation ϕ should decrease as EF is shifted upward by increasing electronic N. To resolve this puzzle, we performed Hall effect measurements, hard/soft-x-ray, and ultraviolet photoelectron spectroscopy on polycrystalline Sn-doped In2O3 films treated with KrF-ELI (λ = 248 nm). Our data reveal that the contradiction resides in astonishingly distinct ELI effects between bulk and the surface. Namely, ELI generates electronic carriers in the bulk via extrinsic (Sn)-dopant activation, while it depopulates the carriers on the surface that causes a huge (1.1 eV) surface-band-bending reversal from downward (electron-accumulation) to upward (-depletion). The spectroscopic evidence reveals that higher ϕ and N were obtained by ELI in vacuum than in the air atmosphere. Our results suggest that ELI is a promising technique for fabricating high-performance TCO for OLED applications.

Tailoring of carrier concentration and engineering of band gap for Sn-doped In2O3 films by postirradiation of negatively charged oxygen ions

We demonstrate that the state-of-the-art postirradiation technology for negatively charged oxygen (O−) ions is effective for tailoring carrier concentration (n e ), electrical resistivity (ρ), and optical band gap (E g) in a wide range for polycrystalline 50-nm-thick Sn-doped In2O3 (ITO) films on glass substrates by reactive plasma deposition with direct-current arc discharge. As-deposited ITO films showed n e of 9.2 × 1020 cm−3, ρ of 1.5 × 10−4 Ω cm, and E g of 3.50 eV. The postirradiation of O− ions for 180 min at 250 °C decreased n e to 2.4 × 1018 cm−3. This resulted in a significant increase in ρ to 3.5 × 10−1 Ω cm while retaining the bixbyite crystal structure and the spatial distribution of Sn dopant atoms. The postirradiation of O− ions led to the continuous decrease in the optical E g ranging from 3.50 to 3.02 eV, which is smaller than that of undoped In2O3. For degenerate ITO films, conventional theories about the broadening and narrowing of the optical E g explain the experimental results well. On the other hand, for nondegenerate ITO films, the optical E g shrinkage would be mainly caused by an upward energy shift attributable to the generation of the anti-bonding π* states between O 2p and In 4d orbitals within the topmost valence band owing to the lattice disorder associated with incorporated interstitial oxygen atoms that fill structural vacancy sites. On the basis of the Ioffe–Regel criterion utilizing the electron mean free path, Fermi momentum, and their product, we determined the critical n e at which degenerate ITO films transform to nondegenerate ones.

Growth and vacuum post-annealing effect on the structural, electrical and optical properties of Sn-doped In2O3 thin films

Nowadays, the fabrication of cheaper, thermodynamically stable and durable transparent semiconducting oxide-based thin films are on high demand to enhance the properties of optoelectronic, sensing and energy harvesting devices. It is well known that Sn-doped In2O3 (ITO) thin films are difficult to grow by direct current sputtering. However, in this work cost-effective Sn-doped In2O3 films are deposited onto borosilicate glass substrates using a direct current sputtering of metallic In/Sn-target. The film thickness was controlled by the deposition time. A post-deposition annealing of the films in a vacuum atmosphere was performed in order to control the structural, optical and electrical properties. The phase formation, crystallite grain sizes (D) and lattice parameters have been assessed from the X-ray diffraction data analysis. Cross-section Scanning electron microscope image analyses were performed in order to estimate the growth rate of thin films. A band gap energy closing was observed associated with relaxation process of the unit cell suggested by the monotonic reduction of the lattice constant. Besides, a low sheet resistance (44 Ohm/square) was obtained, which is comparable to the commercially available ITO films. Furthermore, a inverse-square dependence between the sheet resistance and the grain size was determined (Rsq ∼ 1/D2). The last was used to estimate the carrier concentration of the thicker film ∼ 1020cm−3, which is in agreement with the value obtained from the Hall measurement.

Evolution of implicate order from amorphous to polycrystalline Sn-doped In2O3 films determined by in situ two-dimensional X-ray diffraction measurements

We elucidated implicate ordering of amorphous Sn-doped In2O3 films grown on glass substrates during the phase transition to polycrystalline by postannealing from room temperature to 300 °C for 55 min. X-ray diffraction with two-dimensional detector revealed the following. First, fine grains are developed. Second, crystallites are grown with (222) preferential orientation associated with growing crystallites along (222) plane. Simultaneously, the alignment between grains is also promoted. Finally, while retaining the alignments among crystallites, long-range ordering was improved within the crystallites. Based on those findings, as a well-defined crystallization temperature, we propose a temperature at which the above-mentioned final stage starts.

Tailoring of Point Defects in Polycrystalline Indium Tin Oxide Films with Postirradiation of Electronegative Oxygen Ions

We have developed a state-of-the-art technology to tailor oxygen-related point defects such as oxygen vacancies (VO) and structural defects of polycrystalline highly conductive Sn-doped In2O3 (ITO) films by a postirradiation of electronegative oxygen (O–) ions. The intentional oxygen doping that would annihilate VO decreases carrier density (ne) from 9.3 × 1020 to 7.1 × 1020 cm–3 with an increase of Hall mobility (μH) from 44 to 51 cm2·V−1·s−1, and subsequently, ne drastically decreases down to 1.2 × 1019 cm–3 together with a decrease in μH owing to a formation of Sn–O neutral complexes with a further increase in the amount of oxygen atoms that should fill the structural defects while retaining their crystal structure. Upon the filling of the structural vacancies, the successful control of intrinsic point defects is probably caused by almost no difference in the ionic radii between In3+ having six-coordination and Sn4+ having eight-coordination. The O–-ion-irradiation technology enables one to tailor the ...

Effects of thickness on photoelectric properties and perovskite solar cells application of transparent conductive F and Al co-doped ZnO films

ZnO films with excellent photoelectric properties have been realized in this study through low-concentration F-and-Al co-doping, conducted with radio-frequency magnetron sputtering. It has been demonstrated that the valence state of Al gradually changes from the incomplete oxidation state to the oxidation state, though the chemical valence states of F, O, and Zn are stable. The as-prepared films possess good performance with a mobility of ∼41.89 cm2/Vs, resistivity of ∼3.50 × 10−4 Ω cm, and an average transmittance over 90% in the range of 400–1200 nm. Moreover, the crystallinity of the films and effect of Al doping were further improved through post annealing. Consequently, the improved film mobility, carrier concentration, resistivity, and sheet resistance were, respectively, measured as 53.97 cm2/Vs, 5.18 × 1020 cm−3, 2.23 × 10−4 Ω cm, and 2.73 Ω/□. These films are, therefore, superior to the commercial F-doped SnO2 (FTO) and comparable to the Sn-doped In2O3 (ITO) films. High-performance perovskite with a conversion efficiency as high as 16.24% was achieved when the abovementioned optimized film was used as the front electrode. The reference perovskite solar cells that had commercial ITO and FTO as their front electrodes showed lower efficiency of 15.92% and 12.45%, respectively.

Highly transparent and flexible TiN doped In2O3 (ITON)/Ag-Ti/ITON multilayer electrodes coated on polyethylene terephthalate substrate

We investigated characteristics of TiN doped In2O3 (ITON)/Ag-Ti/ITON multilayer films prepared by using co-sputtering and thermal evaporation at room temperature to use as transparent and flexible electrodes. The optimized ITON(40 nm)/Ag-Ti(14 nm)/ITON(40 nm) multilayer film showed a sheet resistance of 4.136 Ohm/square and an average transmittance of 86.45% at visible range between 400 and 800 nm. In addition, the ITON/Ag-Ti/ITON multilayer film exhibited a constant resistance change (R/R0) below critical outer bending radius of 6 mm, which is smaller than typical Sn-doped In2O3 films. At dynamic fatigue tests, the ITON/Ag-Ti/ITON film showed a constant resistance change during 10,000 times repeated outer/inner bending cycles due to outstanding flexibility of the Ag-Ti interlayer and amorphous structure of the ITON layer. Low sheet resistance, high optical transmittance, and outstanding mechanical properties of ITON/Ag-Ti/ITON multilayer films indicate that ITON-based hybrid electrode is promising flexible and transparent electrodes for high performance flexible photovoltaics.

Effects of oxygen partial pressure on the microstructure, electrical and optical properties of the Sn-doped In2O3 thin films

The effects of oxygen partial pressure on the microstructure, electrical and photo-sensitive properties of the Sn-doped In2O3 (ITO) films deposited by different Ar–O2 flow rates (10:0.4, 10:1, 10:1.8 and 10:3) were investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect, UV-Vis and optical measurements. The XRD and SEM measurements show that the ITO film deposited at oxygen flow rate of 0.4 sccm prefers to (400) orientation and has a rough sawtooth-shaped surface. However, the ITO films deposited at oxygen flow rates of 1 sccm, 1.8 sccm and 3 sccm prefer to (222) orientation and exhibit a flat smooth surface. The conductivity, mobility and photosensitive property of ITO films are also sensitive to oxygen flow rate. The ITO film deposited at oxygen flow rate of 0.4 sccm has a high carrier concentration (up to [Formula: see text] cm[Formula: see text]) and mobility (16.7 cm2/vs), low resistivity [Formula: see text], and a long response time but good sensitivity to ultraviolet light. It can be concluded that the surface morphology plays a dominant role in sensitivity to ultraviolet light. The good sensitivity of ultraviolet light is gained from the ITO film with sawtooth-shaped surface.

Investigation of the role of deposition rate on optical, microstructure and ethanol sensing characteristics of nanostructured Sn doped In2O3 films

In this paper, Sn doped In2O3 (In2O3:Sn) nanostructured films as metal oxide semiconductor material which is very important in optoelectronics and gas sensing industries, were prepared by thermal evaporation technique. It is discussed how different deposition rate (0.1, 0.2, 0.3 and 0.4 nm/s) affects the optical, electrical, microstructural and ethanol gas sensing characteristics of In2O3:Sn films and must be precisely monitored. The gas sensing performance of the films was evaluated in terms of gas concentration and operating temperature. A correlation between the crystallite size, porosity, dislocation density, outer cut-off radius of dislocation, optical band gap, activation energy and sensitivity of the films was established. The results demonstrate that the maximum sensitivity to ethanol vapors can be obtained for the sample grown at deposition rate of 0.2 nm/s. The response and recovery times of this sensor exposed to 100 ppm of ethanol vapors were determined and found to be 9.0 s and 3.9 s, respectively.

The effects of film thickness on the electrical, optical, and structural properties of cylindrical, rotating, magnetron-sputtered ITO films

We report the characteristics of Sn-doped In2O3 (ITO) films intended for use as transparent conducting electrodes; the films were prepared via a five-generation, in-line type, cylindrical, rotating magnetron sputtering (CRMS) system as a function of film thickness. By using a rotating cylindrical ITO target with high usage (∼80%), we prepared high conductivity, transparent ITO films on five-generation size glass. The effects of film thickness on the electrical, optical, morphological, and structural properties of CRMS-grown ITO films are investigated in detail to correlate the thickness and performance of ITO films. The preferred orientation changed from the (2 2 2) to the (4 0 0) plane with increasing thickness of ITO is attributed to the stability of the (4 0 0) plane against resputtering during the CRMS process. Based on X-ray diffraction, surface field emission scanning electron microscopy, and cross-sectional transmission electron microscopy, we suggest a possible mechanism to explain the preferred orientation and effects of film thickness on the performance of CRMS-grown ITO films.

Cerium oxide and hydrogen co-doped indium oxide films for high-efficiency silicon heterojunction solar cells

CeO2 and hydrogen co-doped In2O3 (ICO:H) films deposited by ion plating with dc arc-discharge were used as a transparent conducting oxide (TCO) electrode in hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction (SHJ) solar cells. Incorporating ICO:H instead of conventional Sn-doped In2O3 (ITO) films and hydrogenated In2O3 (IO:H) films, improved the fill factor (FF) and short-circuit current density (Jsc) simultaneously. The best SHJ cell (243.4cm2) containing ICO:H films had a conversion efficiency of 24.1%, open-circuit voltage of 745mV, Jsc of 38.8mA/cm2, and FF of 83.2% because of their high Hall mobility of 140cm2/Vs. We have clarified the following design principles for ICO:H films: (i) the Ce species substituted for In atoms acts as a donor and (ii) CeO2 and H decrease the residual strain and the contribution of the grain boundary scattering to carrier transport. This co-doping method can produce high conversion efficiencies in all solar cells containing TCO with resistive emitters.