Thin Indium Tin Oxide Research Articles

Optical constants and thickness gradients for light intensities in glass substrate layers and for complex electric fields in indium tin oxide (ITO) transparent conductor thin film layer, using Bode and Nyquist wavelength-dependent diagrams

Abstract The optical constants of a thin film layer of transparent conductive indium tin oxide (ITO), deposited on a thick glass substrate (G), were obtained for an ITO-G sample using a multilayer matrix method by fitting the regular transmittance and specular reflectance measurements to the collimated equations of the four-flux model, once the optical constants of the glass substrate layer had previously been obtained from a G sample of a single glass substrate layer. The accuracy of the results was validated using a feedback system called the three-extinction matching requirement, that is, obtaining the same extinction coefficients from the optical constants and from the forward and backward collimated differential equations of the four-flux model. To calculate the extinction coefficients of the glass from optical constants, the compression of the wavelength of the incident light in the glass substrate and in the thin ITO film layer was demonstrated, with a thickness less than the wavelength of incident light. The thickness gradients of the forward and backward collimated light intensities, on the glass substrate of the ITOG sample, were compared with those obtained for the single-layer G sample. Then, the thickness gradients for the complex forward and backward electric fields of the ITO thin film layer were obtained and plotted using spectral magnitude and phase Bode plots and new Nyquist plots, i.e. imaginary versus real parts, dependent on wavelength.

Multiscale Fabrication Process Optimization of DFB Cavities for Organic Laser Diodes.

In the context of the quest for the Organic Laser Diode, we present the multiscale fabrication process optimization of mixed-order distributed-feedback micro-cavities integrated in nanosecond-short electrical pulse-ready organic light-emitting diodes (OLEDs). We combine ultra-short pulsed electrical excitation and laser micro-cavities. This requires the integration of a highly resolved DFB micro-cavity with an OLED stack and with microwave electrodes. In a second challenge, we tune the cavity resonance precisely to the electroluminescence peak of the organic laser gain medium. This requires precise micro-cavity fabrication performed using e-beam lithography to pattern gratings with a precision in the nanometer scale. Optimal DFB micro-cavities are obtained with 300 nm thick hydrogen silsesquioxane negative-tone e-beam resist on 50 nm thin indium tin oxide anode exposed with a charge quantity per area (i.e., dose) of 620 µC/cm2, developed over 40 min in tetramethylammonium hydroxide diluted in water. We show that the integration of the DFB micro-cavity does not hinder the pulsed electrical operability of the device, which exhibits a peak current density as high as 14 kA/cm2.

Large second-order susceptibility from a quantized indium tin oxide monolayer.

Due to their high optical transparency and electrical conductivity, indium tin oxide thin films are a promising material for photonic circuit design and applications. However, their weak optical nonlinearity has been a substantial barrier to nonlinear signal processing applications. In this study, we show that an atomically thin (~1.5 nm) indium tin oxide film in the form of an air/indium tin oxide/SiO2 quantum well exhibits a second-order susceptibility χ2 of ~1,800 pm V-1. First-principles calculations and quantum electrostatic modelling point to an electronic interband transition resonance in the asymmetric potential energy of the quantum well as the reason for this large χ2 value. As the χ2 value is more than 20 times higher than that of the traditional nonlinear LiNbO3 crystal, our indium tin oxide quantum well design can be an important step towards nonlinear photonic circuit applications.

Identification and classification of Eremogone species using DNA based Schottky diodes

The revelation of DNA's remarkable conducting characteristics provided a significant boost for the development of DNA-based electronics. These distinguishing characteristics can be used to identify or detect DNA. In this study, it was basically aimed to investigate the possibility of using Schottky barrier diodes in which semiconductor DNA is used as the interface from three endemic Eremogone species distributed in Turkey. We collected Eremogone ali-gulii, Eremogone armeniaca, and Eremogone scariosa endemic species and extracted the DNA via the QIAGEN commercial DNA isolation kit procedure. The DNA samples were deposited by drop casting on the thin film indium tin oxide substrate. Electrical characterization of DNA interlayered heterojunctions was investigated via a solar simulator. Electronic parameters such as ideality factor, barrier height, and series resistance were calculated from I to V characteristics. Electrical properties of DNA samples were investigated and compared to Colchicum triphyllum’s DNA which is completely from another genus. The results show that morphologically similar species have similar electrical properties. When compared to Colchicum triphyllum-DNA based device, genus Eremogone-DNA based devices have a lower ideality factor, barrier height, and series resistance. Via this technique, DNA samples can be identified, detected, and classified.

Performances of Nano-Structured Cu2O Thin Films Electrochemically Deposited on ITO Substrates in Lactate Bath as Liquid Petroleum Gas Sensors

The investigations are focused on structural and surface morphological features and their influence on electrical and wetting characteristics against liquid petroleum gas (LPG) sensing of synthesized nanostructured cuprous oxide (Cu2O) thin films grown by electrochemical deposition (ECD) on indium tin oxide (ITO) glass substrates in lactate bath (pH 10). p-Cu2O films revealed a cubical-tetrahedron nano-scale polycrystalline grain distribution (average grain size: 64.2 nm, inter planer spacing: 0.24 nm) that exhibited dominance in the crystallographic plane (111). LPG sensing evaluations of p-Cu2O/ITO done at 70 °C constant temperature with 100% LPG at 5 cc min−1 flow rate, showed excellent gas sensor response, recovery, and stability over time due to its moderate wetting behavior (average contact angle: ∼86°). AC impedance measurements carried out at room temperature demonstrated an ionic to electronic conduction variation from 100 Hz to 1 MHz, due to adsorption/desorption of LPG molecules (CnH2n+2) and oxygen species on the nano-particles surface. Cu2O/ITO flat band potential was found to be higher than its’ ambient state after exposure to LPG with an increment in acceptor density. Overall, this efficient LPG sensing could be attributed to the interfacial properties of Cu2O thin films and ITO substrates, that provide an optimized fabrication process of nano-structured Cu2O thin films.

Efficient optical modulation in ring structure based on Silicon-ITO heterojunction with low voltage and high extinction ratio

We numerically propose a low voltage, high extinction ratio optical modulator with a tunable group delay in a resonance enhanced ring resonator based on Silicon (Si) - Indium Tin Oxide (ITO) heterojunction. This is accomplished by incorporating a thin ITO layer into a Si-ring resonator. By electrically inducing carrier changes in ITO, the epsilon-near-zero (ENZ) state of ITO is attained, resulting in a sudden change in optical absorption. The resonance condition shifts because of the ENZ state, and the transmission at the ring resonator’s through port changes dramatically. The extinction ratio (ER) of 11 dB at a low forward bias of 1 V is reported with a low energy consumption of 2.6 fJ. An optical network has a non-trivial demand for a high extinction ratio optical modulator that operates at a low driving voltage and consumes minimal energy. The proposed ring modulator with a high extinction ratio at low driving voltage outperforms conventional waveguide-based modulators in terms of energy efficiency. In addition, we report around 25 psec of electrical tuning in the group delay The current concept has favorable results in terms of exploring tunable delay lines in conjunction with optical modulation with a high extinction ratio.

Porous Copper Oxide Thin Film Electrodes for Non-Enzymatic Glucose Detection

The present work describes novel copper oxide thin film-modified indium tin oxide electrodes prepared by magnetron sputtering and their application for glucose sensing. Copper oxide-modified sensors were characterized by electrochemical techniques, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The deposited thin film (of about 400 nm of thickness) consisted of Cu2O/CuO nanocolumns of ca. 80 nm in diameter. After optimizing the main experimental parameters, the electrodes showed noteworthy electrocatalytic properties for glucose detection (sensitivity ca. 2.89 A M−1 cm−2 and limit of detection ca. 0.29 μM (S/N = 3)). The sensor showed negligible response against common electroactive species and other sugars. Finally, recovery experiments in commercial soda drinks and the determination of glucose content in different commercial drinks, such as soda, tea, fruit juices, and sports drinks, are described.

Static and transient optical properties of thin film indium tin oxide during laser excitation

The mechanisms of ultrafast laser-induced free electron generation and the effect of the free electrons on the transient optical properties in indium tin oxide is investigated by means of numerically solving rate equations and ultrafast transient experiments. A dynamical model for the transient optical properties of indium tin oxide thin films during excitation with an ultrashort laser pulse with fluences between 0.4 J cm−2 to 2.3 J cm−2 is developed and compared to pump probe microscopy during and after excitation with laser pulses. In the non-excited case, thin film interferences dominate the shape of the reflection spectrum. During laser excitation, (quasi-)free electron dynamics drastically alter the optical properties. The temporal evolution of the (quasi-)free electron density is numerically computed using rate equations for irradiation with laser pulses with various peak fluences for a pulse duration of 700 fs and a central wavelength of 1056 nm. We found that a thermal ionization term that takes electronic states within the band gap into account has to be considered to reproduce the reflectivities obtained by pump probe measurements. Additionally, we found that cascade ionization dominates the multiphoton ionization for indium tin oxide.

Dynamic Nanophotonics in Epsilon‐Near‐Zero Conductive Oxide Films and Metasurfaces: A Quantitative, Nonlinear, Computational Model

The promise of dynamic nanophotonic technologies relies on the confinement and spatiotemporal control of light at the nanoscale. Confinement via plasmonics, dielectric resonators, and waveguides can be complemented with materials whose optical properties can be controlled using nonlinear effects. Transparent conducting oxides (TCOs) exhibit strong optical nonlinearities in their near‐zero permittivity spectral region, on the femtosecond timescale. Harnessing full spatiotemporal control over the nonlinear response requires a deeper understanding of the process. To achieve this, a self‐consistent multiphysics time‐domain model for the nonlinear optical response of TCOs is developed and implemented into a 3D finite‐difference time‐domain code. Simulations are compared and tuned against recently published experimental results for intense laser irradiation of thin indium tin oxide (ITO) films, achieving good quantitative agreement; the time‐domain dynamics of the nonlinear response and the phenomenon of time‐refraction are also explored. Finally, by simulating intense laser irradiation of a plasmonic particle on an ITO film, the applicability of the approach to time‐varying metasurfaces is demonstrated. As expected, significant enhancement of the nonlinear response of an ITO‐based metasurface over bare ITO thin films is found. This work thus enables quantitative nanophotonics design with conductive oxides in their epsilon‐near‐zero region.

Strongly Coupled Plasmon Polaritons in Gold and Epsilon-Near-Zero Bifilms.

Epsilon-near-zero (ENZ) polaritons in a thin transparent conducting-oxide film exhibit a significant electric field enhancement and localization within the film at frequencies close to their plasma frequency, but do not propagate. Meanwhile, plasmon polariton modes in thin metallic films can propagate for several microns, but are more loosely confined in the metal. Here, we propose a strongly coupled bilayered structure of a thin gold film on a thin indium tin oxide (ITO) film that supports hybrid polariton modes. We experimentally characterize the dispersion of these modes and show that they have propagation lengths of 4-8 μm while retaining mode confinement greater than that of the polariton in gold films by nearly an order of magnitude. We study the tunability of this coupling strength by varying the thickness of the ITO film and show that ultrastrong coupling is possible at certain thicknesses. The unusual linear and nonlinear optical properties of ITO at ENZ frequencies make these bifilms useful for the active tuning of strong coupling, ultrafast switching, and enhanced nonlinear interactions at near-infrared frequencies.

Hot Carrier-Induced Nonlinear Photoluminescence in a Thin Indium Tin Oxide Layer Patterned by Ga Ion Beam Milling

This paper explores the nonlinear photoluminescence emitted by indium tin oxide (ITO) thin layers patterned by focused gallium ion beam milling. Using tightly focused near-infrared femtosecond pulsed laser excitation, a broad up-converted luminescence spectrum spanning the visible is detected. The intensity of the luminescence follows a nonmonotonous relationship with milling doses and can be related to the modification of the ITO electronic band structure by the implantation of Ga ions. The shape and the power dependence of the spectrum share strong similarities with those of nonlinear photoluminescence arising from metals. The results are consistent with a nonlinear process originating from the radiative decay of photogenerated hot carriers. The thermal coefficient relating the carrier temperature to the laser intensity is determined as a function of milling dose.

The Role of Epsilon Near Zero and Hot Electrons in Enhanced Dynamic THz Emission from Nonlinear Metasurfaces.

We study theoretically and experimentally the nonlinear THz emission from plasmonic metasurfaces and show that a thin indium-tin oxide (ITO) film significantly affects the nonlinear dynamics of the system. Specifically, the presence of the ITO film leads to 2 orders of magnitude stronger THz emission compared to a metasurface on glass. It also shows a different power law, signifying different dominant emission mechanisms. In addition, we find that the hot-electron dynamics in the system strongly modify the coupling between the plasmonic metasurface and the free electrons in the ITO at the picosecond time scale. This results in striking dynamic THz emission phenomena that were not observed to date. Specifically, we show that the generated THz pulse can be shortened in time and thus broadened in frequency with twice the bandwidth compared to previous studies and to an uncoupled system. Our findings open the door to design efficient and dynamic metasurface THz emitters.

P-i-n Perovskite Solar Cells on Steel Substrates.

An efficient substrate-configuration p–i–n metal-halide perovskite solar cell (PSC) is fabricated on a polymer-coated steel substrate. The optimized cell employs a Ti bottom electrode coated with a thin indium tin oxide (ITO) interlayer covered with a self-assembled [2-(9H-carbazol-9-yl)ethyl]phosphonic acid monolayer as a hole-selective contact. A triple-cation perovskite is used as the absorber layer. Thermally evaporated C60 and atomic layer deposited SnO2 layers serve to create an electron-selective contact. The cells use an ITO top electrode with an antireflective MgF2 coating. The optimized cell fabricated on a polymer-coated steel substrate reaches a power conversion efficiency of 16.5%, which approaches the 18.4% efficiency of a p–i–n reference superstrate-configuration cell that uses a similar stack design. Optical simulations suggest that the remaining optical losses are due to the absorption of light by the ITO top electrode, the C60 layer, the Ti bottom electrode, and reflection from the MgF2 coating in almost equal amounts. The major loss is, however, in the fill factor as a result of an increased sheet resistance of the top ITO electrode.

Thermal behavior of AlGaN-based deep-UV LEDs.

This study utilized thin p-GaN, indium tin oxide (ITO), and a reflective passivation layer (RPL) to improve the performance of deep ultra-violet light-emitting diodes (DUV-LEDs). RPL reflectors, which comprise HfO2/SiO2 stacks of different thickness to maintain high reflectance, were deposited on the DUV-LEDs with 40 nm-thick p-GaN and 12 nm-thick ITO thin films. Although the thin p-GaN and ITO films affect the operation voltage of DUV-LEDs, the highly reflective RPL structure improved the WPE and light extraction efficiency (LEE) of the DUV-LEDs, yielding the best WPE and LEE of 2.59% and 7.57%, respectively. The junction temperature of DUV-LEDs with thick p-GaN increased linearly with the injection current, while that of DUV-LEDs with thin p-GaN, thin ITO, and RPL was lower than that of the Ref-LED under high injection currents (> 500 mA). This influenced the temperature sensitive coefficients (dV/dT, dLOP/dT, and dWLP/dT). The thermal behavior of DUV-LEDs with p-GaN and ITO layers of different thicknesses with/without the RPL was discussed in detail.

Novel Ag‐Mesh Transparent Hybrid Electrodes for Highly Efficient and Mechanically Stable Flexible Perovskite Solar Cells

AbstractMetal‐mesh transparent conductive electrodes (TCEs)‐based flexible perovskite solar cells (FPSCs) have been intensively explored to improve the efficiency and stability of the devices, whereas undesired metal‐induced decomposition of perovskite during film formation process could undermine the performance and stability of device. In this work, the authors construct a novel flexible hybrid electrode combining silver (Ag) mesh‐embedded poly(ethylene terephthalate) film (PET/Ag‐mesh) with a thin indium tin oxide (ITO) layer, named PET/Ag‐mesh/ITO, which exhibits outstanding photoelectric properties, chemical stability, and mechanical durability. They introduce the thin ITO film as a barrier layer to protect perovskite from the metal‐induced degradation. In comparison, the PET/Ag‐mesh/ITO based FPSCs achieve an optimized power conversion efficiency (PCE) of 18.10%, which is among the highest reported values for metal‐mesh based FPSCs to date. Owing to the excellent properties of PET/Ag‐mesh/ITO, the corresponding FPSCs demonstrate extraordinary mechanical and thermal stability, which is comparable to that of their rigid ITO‐based counterparts.

12.42% Monolithic 25.42 cm2 Flexible Organic Solar Cells Enabled by an Amorphous ITO-Modified Metal Grid Electrode.

Printed metal nanogrid electrode exhibits superior characteristics for use in flexible organic solar cells (OSCs). However, the high surface roughness and inhomogeneity between grid and blank region is adverse for performance improvement. In this work, a thin amorphous indium tin oxide (ITO) film (α-ITO) is introduced to fill the blank and to improve the charge transporting. The introduction of α-ITO significantly improves the comprehensive properties of metal grid electrode, which exhibits excellent bending resistance and long-term stability under double 85 condition (under 85°C and 85% relative humidity) for 200 h. Both experimental and simulation results reveal α-ITO with a sheet resistance of 20 000 Ω □-1 is sufficient to improve the charge transporting within the adjacent grids, leading to a remarkable efficiency of 16.54% for 1 cm2 flexible devices. With area increased to 4.00, 9.00, and 25.42 cm2 , the devices still display a performance of 16.22%, 14.69%, and 12.42%, respectively, showing less efficiency loss during upscaling. And the 25.42 cm2 monolithic flexible device exhibits a certificated efficiency of 12.03%. Moreover, the device shows significantly improved air stability relative to conventional high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-modified device. All these make the α-ITO-modified Ag/Cu electrode promise to achieve high-efficient and long-term stable large-area flexible OSCs.

Semitransparent near-infrared Sn–Pb hybrid perovskite photodetectors

We report semitransparent NIR perovskite photodetectors based on tin–lead hybrid perovskites, by using very thin film perovskite layers and transparent indium tin oxide electrodes.

Nanostructured Strontium Titanate Perovskite Hyperbolic Metamaterial Supported Tunable Broadband THz Brewster Modulator

The investigation was made of nanostructured intensity and phase modulators, the designs of which are based on Brewster angle manipulation. The configuration consists of thin indium tin oxide, strontium titanate and quartz layers embedded on silicon substrate. The structure exhibits elliptical and hyperbolic metamaterial kinds, which can be manipulated by varying the ambient temperature. The design yields broadband intensity and phase modulator with 99.8% modulation depth and perfect phase shift (i.e., 180°), respectively, at the room temperature. This would find potentials in active polarization switches, modulators and tunable phase shifters operating in the THz regime.

Effect of rapid thermal treatment on the electrical conductivity improvement of nc-ZnO:Bi thin film and ITO substrate

Spherical nano crystalline zinc oxide doped with bismuth (nc-ZnO:Bi) spin-coated on indium tin oxide (ITO) substrates exhibited the improvement of conductivity under the rapid thermal annealing (RTA) treatment. The ZnO:Bi nanostructure was formed at 550 °C annealing temperature, which severely affect the ITO electrical quality and closely relevant with the device performance. The efficiency of relevant electronic devices has been limited by the low electrical conductivity of the transparent electrodes. RTA treatment in the ambient atmosphere condition was applied to ZnO:Bi film coated on ITO substrate to perform the good spherical nc-ZnO:Bi properties and to persist in the ITO low resistivity, concomitantly which results in significant improvement of electrical and optical properties of nc-ZnO:Bi/ITO substrate. RTA process was subjected at varying temperature conditions from 700 °C to 930 °C for 20 s. It is noticeable that the RTA can obtain ZnO:Bi nanostructure, good optical property, and high ITO conductivity existence, simultaneously. The nano-spherical ZnO:Bi around 10–20nm diameter size at the film surface morphology provides the reflectance of 6%, and the transmittance of above 90% at 930 °C RTA for 20 s. The photocurrent of nc-ZnO:Bi/ITO films provides between 10−2 to 1 A/cm2 at 0.5 V. The RTA process can improve electrical property of ITO films with uniform distribution of oxygen vacancy. Surface morphology and crystalline grain quality of the thin film were investigated after RTA treatment. In addition, optical absorbance and energy gap (Eg) of nc-ZnO:Bi/ITO substrate evaluated by Tauc plot is a crucial attribute to apply in a promising photonic device. Thus, the high electrical and optical qualities of such nc-ZnO:Bi/ITO films can be used to produce an electron transport layer for organic solar cells and transparent contact electrodes for low-cost semiconductor devices.

Adapting confocal Raman microscopy for in situ studies of redox transformations at electrode-electrolyte interfaces

Confocal Raman microscopy was applied to quantify redox species present within the diffusion layer adjacent to an electrode surface under potentiostatic control. A glass microscope coverslip with a thin indium tin oxide (ITO) coating served as both the working electrode and optical window for a microscope-stage mountable spectroelectrochemical cell. A high numerical aperture objective mounted in an inverted microscope frame just below the stage brought excitation radiation through the coverslip window and to a tight focus a few micrometers above the ITO film surface. Species diffusing into the confocal probe volume defined by the excitation beam focus and the collected light region were detected, identified and quantified based on their Raman scattering frequencies and intensities. In measurements that interrogated the interconversion of ferrocyanide and ferricyanide ions as a function of applied voltage, least-squares regression analysis of spectral datasets predicted the formal potential and relative surface concentrations of the ions in good agreement with the expected Nernstian response. Preliminary studies of methyl viologen reduction at an ITO film/Nafion membrane interface were conducted and show the possibility for estimation of mass transport coefficients of redox species within ionic polymer materials.