In2O3 Layers Research Articles

Saturation Mobility of 100 cm2 V-1 s-1 in ZnO Thin-Film Transistors through Quantum Confinement by a Nanoscale In2O3 Interlayer Using Spray Pyrolysis.

In this study, we present a comprehensive study on the fabrication and characterization of heterojunction In2O3/ZnO thin-film transistors (TFTs) aimed at exploiting the quantum confinement effect to enhance device performance. By systematically optimizing the thickness of the crystalline In2O3 (c-In2O3) layer to create a narrow quantum well, we observed a significant increase in saturation mobility (μSAT) from 12.76 to 97.37 cm2 V-1 s-1. This enhancement, attributed to quantum confinement, was achieved through the deposition of a 3 nm c-In2O3 semiconductor via spray pyrolysis. Various In2O3 layer thicknesses (2-5 nm) were obtained by adjusting precursor solution concentration, flow rate, and number of spray cycles. Post annealing treatments were employed to reduce the defects at the interface and within the oxide film, enhancing device stability and performance. Transmission electron microscopy (TEM) confirmed the uniformity of the c-In2O3 film thickness, while variations in thickness significantly influenced TFT performance, particularly the turn-on voltage (VGS) due to changes in the carrier concentration. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) supported the formation of a potential well with a two-dimensional electron gas (2DEG). The study of single and multiple superlattice structures of consecutive c-In2O3 and c-ZnO layers provided insights into the effects of multiple quantum wells on the TFT performance. This research presents an advanced approach to TFT optimization, highlighting high reliability, and environmental and bias stabilities. These lead to enhanced mobility and performance uniformity through the precise control of c-In2O3 layer thickness for the quantum confinement effect.

Gas Sensing with Nanoporous In2O3 under Cyclic Optical Activation: Machine Learning-Aided Classification of H2 and H2O

Clean hydrogen is a key aspect of carbon neutrality, necessitating robust methods for monitoring hydrogen concentration in critical infrastructures like pipelines or power plants. While semiconducting metal oxides such as In2O3 can monitor gas concentrations down to the ppm range, they often exhibit cross-sensitivity to other gases like H2O. In this study, we investigated whether cyclic optical illumination of a gas-sensitive In2O3 layer creates identifiable changes in a gas sensor’s electronic resistance that can be linked to H2 and H2O concentrations via machine learning. We exposed nanostructured In2O3 with a large surface area of 95 m2 g−1 to H2 concentrations (0–800 ppm) and relative humidity (0–70%) under cyclic activation utilizing blue light. The sensors were tested for 20 classes of gas combinations. A support vector machine achieved classification rates up to 92.0%, with reliable reproducibility (88.2 ± 2.7%) across five individual sensors using 10-fold cross-validation. Our findings suggest that cyclic optical activation can be used as a tool to classify H2 and H2O concentrations.

Rapid Surface Reconstruction of In2S3 Photoanode via Flame Treatment for Enhanced Photoelectrochemical Performance.

Surface reconstruction, reorganizing the surface atoms or structure, is a promising strategy to manipulate materials' electrical, electrochemical, and surface catalytic properties. Herein, a rapid surface reconstruction of indium sulfide (In2S3) is demonstrated via a high-temperature flame treatment to improve its charge collection properties. The flame process selectively transforms the In2S3 surface into a diffusionless In2O3 layer with high crystallinity. Additionally, it controllably generates bulk sulfur vacancies within a few seconds, leading to surface-reconstructed In2S3 (sr-In2S3). When using those sr-In2S3 as photoanode for photoelectrochemical water splitting devices, these dual functions of surface In2O3/bulk In2S3 reduce the charge recombination in the surface and bulk region, thus improving photocurrent density and stability. With optimized surface reconstruction, the sr-In2S3 photoanode demonstrates a significant photocurrent density of 8.5mA cm-2 at 1.23V versus a reversible hydrogen electrode (RHE), marking a 2.5-fold increase compared to pristine In2S3 (3.5mA cm-2). More importantly, the sr-In2S3 photoanode exhibits an impressive photocurrent density of 7.3mA cm-2 at 0.6V versus RHE for iodide oxidation reaction. A practical and scalable surface reconstruction is also showcased via flame treatment. This work provides new insights for surface reconstruction engineering in sulfide-based semiconductors, making a breakthrough in developing efficient solar-fuel energy devices.

Facile routes to enhance doping efficiency using nanocomposite structures for high-mobility and stable PEALD-ITGO TFTs

In–Sn–Ga–O (ITGO) thin-film transistors (TFTs) fabricated by atomic layer deposition (ALD) are promising candidates for widespread semiconductor applications because of their high mobility and stability. To further improve the device characteristics, the doping efficiency of each cation must be increased. Here, we propose a facile method to enhance the device characteristics using plasma-enhanced ALD-nanocomposite (NC) structures. The deposition of SnO2 materials within the In2O3 layer of the ITGO film with the NC-ITO structure accelerates the reduction of In2O3 (In0: 35.3 % →46.1 %), thereby stabilizing SnO2 (Sn4+: 71.0 % →89.1 %). In addition, this process significantly decreases the fraction of oxygen-related defects (Odefect: 24.0 % →17.6 %) because Sn–O has a substantially higher bond dissociation energy than In–O. Consequently, the ITGO TFT with the NC-ITO active layer exhibits considerable improvements in the electrical parameters, such as an increase in the field-effect mobility from 41.9 to 54.5 cm2/V s and an enhancement in the subthreshold swing from 69.8 to 64.8 mV/decade. In addition, the device shows excellent results for negative bias illumination stress and positive bias temperature stress, with the differences in the threshold voltage shift being −0.22 and + 0.06 V, respectively.

Crystal structure analysis of self-catalyzed InAs nanowire grown by MOCVD

We studied the crystal structure of self-catalyzed InAs nanowires with different diameters grown on Si Substrate by metal-organic chemical vapor deposition (MOCVD) and found that oxidation degree and nanowire diameter directly affect the lattice structure of InAs nanowire. In the non-oxidized state of InAs nanowires, when the diameter is greater than 160 nm, the lattice structure is mainly cubic zinc blende (ZB) structure. When the diameter is between 121 nm and 80 nm, ZB structure and hexagonal wurtzite (WZ) structure coexist. When the diameter is less than 66 nm, the lattice structure is mainly WZ structure. In the fully oxidized state of InAs nanowires, a stable layer of In2O3 is formed on its surface, and InAsO4 will be formed inside due to infiltrated oxygen atoms. When InAs nanowires are made into nanoelectronic devices as the core material, if oxidation is not prevented, InAs material with excellent electrical conductivity will also become InAsO4.

Solution-processed bilayer InGaZnO/In2O3 thin film transistors at low temperature by lightwave annealing

At low temperatures about 230 °C, bilayer InGaZnO/In2O3 thin film transistors (TFTs) were prepared by a solution process with lightwave annealing. The InGaZnO/In2O3 bilayer TFTs with SiO2 as dielectric layer show high electrical performances, such as a mobility of 7.63 cm2V−1s−1, a threshold voltage (V th) of 3.8 V, and an on/off ratio higher than 107, which are superior to single-layer InGaZnO TFTs or In2O3 TFTs. Moreover, bilayer InGaZnO/In2O3 TFTs demonstrated a great bias stability enhancement due to the introduction of top InGaZnO film act as a passivation layer, which could prevent the interaction of ambient air with the bottom In2O3 layer. By using high dielectric constant AlO x film, the InGaZnO/In2O3 TFTs exhibit an improved mobility of 47.7 cm2V−1s−1. The excellent electrical performance of the solution-based InGaZnO/In2O3 TFTs shows great application potential for low-cost flexible printed electronics.

Investigation of the effect of plasmonic Au nanoparticles on crystalline Si solar cells

In order to increase the photocurrent of tandem solar cells with a silicon (Si) solar cell as the bottom cell, we investigate the relationship between the localized surface plasmon resonance effect of gold nanoparticles (AuNPs) and the arrangement of AuNPs onto solar cells. AuNPs were deposited on P-type crystalline Si (c-Si) cells and Si heterojunction (SHJ) type cells. To obtain the localized surface plasmon resonance effect, the shape, size, and arrangement of the nanostructures are important. Especially, arrangement of AuNPs onto solar cells was inquired in this study because these parameters must be adjusted appropriately to produce a plasmon resonance in a specific wavelength range. It was found that the plasmon resonance effect is significant when deposited on the surface of c-Si cell rather than on top of the Ag electrode. AuNPs deposition on the c-Si cell surface leads to not only the localized surface plasmon resonance effect but also improvement in charge transport between the c-Si cell surface and Ag electrode. However, in the SHJ-type cells, the plasmon resonance effect was not observed because the surface layer was composed of a W-doped In2O3 (IWO) layer.

Exploration of annealing effect on physical properties of Indium oxide films for gas sensors

In the present work, an influence of annealing on physical properties of Indium oxide (In2O3) thin films is investigated for H2S gas sensing applications. The In2O3 films of thickness 450 nm are grown employing physical vapor deposition based electron beam evaporation technique followed by annealing at different temperatures viz. 250 °C, 325 °C and 400 °C for 1 h. XRD analysis indicated crystallization of annealed films in cubic phase having (222) predominant reflection where crystallite size of all the In2O3 layers is tuned in range of 17–26 nm. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. The 2D AFM images of In2O3 films indicated distribution of nano-spherical grains and these In2O3 films also indicated Ohmic nature where resistivity is detected to be enhanced with annealing. Optimized In2O3 films based gas sensors showed gas response of 0.85 and sensor response of 15.38 % towards toxic H2S gas.

Physical properties of thermal annealing induced In2O3 thin films for sensing layer applications

Detection and monitoring of flammable, toxic and explosive gases are crucial, where active research on nanostructured metal oxide materials and thin films is enthusiastically performed to explore new paths for improving the characteristic parameters of sensors. The higher stability and appropriate electrical properties along with wide band gap of In2O3 material make it suitable for active layer to gas sensors where properties of In2O3 films could be engineered by post treatments. The present work demonstrates an influence of thermal annealing on structural, optical, topographical, morphological, elemental and electrical properties of In2O3 films for gas sensor applications. The In2O3 films of thickness 500 nm are grown onto soda lime glass and conducting ITO substrates employing physical vapor deposition based thermal evaporation technique followed by thermal annealing at 200 °C, 300 °C and 400 °C for one hour in air atmosphere. The XRD analysis indicated phase transformation from metastable rhombohedral to stable cubic phase where crystallite size corresponding to associated preferred (110) and (222) peaks is tuned in range of 32–51 nm with annealing. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. All the In2O3 films indicated the Ohmic nature where the resistivity is detected to be enhanced with annealing. EDS patterns confirmed deposition of the films. The SEM analysis showed nanospheres like grain morphology and such well connected nanospheric features offer large surface area and stimulate adsorption of gas effectively. Hence structural, optical, electrical and morphological properties of gas sensitive In2O3 layers are greatly stimulated by thermal annealing.

Dual modification of BiVO4 photoanode for synergistically boosting photoelectrochemical water splitting

Bismuth vanadate (BiVO4) is a promising nanomaterial for photoelectrochemical (PEC) water oxidation. However, the serious charge recombination and sluggish water oxidation kinetics limit its performance. Herein, an integrated photoanode was successfully constructed by modifying BiVO4 (BV) with In2O3 (In) layer and further decorating amorphous FeNi hydroxides (FeNi). The BV/In/FeNi photoanode exhibited a remarkable photocurrent density of 4.0 mA cm−2 at 1.23 VRHE, which is approximately 3.6 times larger than that of pure BV. And the water oxidation reaction kinetics has an over 200% increased. This improvement was mainly because the formation of BV/In heterojunction inhibited charge recombination, and the decoration of cocatalyst FeNi facilitated the water oxidation reaction kinetics and accelerated hole transfer to electrolyte. Our work provides another possible route to develop high-efficiency photoanodes for practical applications in solar conversion.

Tuning the Surface Electron Accumulation Layer of In2 O3 by Adsorption of Molecular Electron Donors and Acceptors.

In2 O3 , an n-type semiconducting transparent transition metal oxide, possesses a surface electron accumulation layer (SEAL) resulting from downward surface band bending due to the presence of ubiquitous oxygen vacancies. Upon annealing In2 O3 in ultrahigh vacuum or in the presence of oxygen, the SEAL can be enhanced or depleted, as governed by the resulting density of oxygen vacancies at the surface. In this work, an alternative route to tune the SEAL by adsorption of strong molecular electron donors (specifically here ruthenium pentamethylcyclopentadienyl mesitylene dimer, [RuCp*mes]2 ) and acceptors (here 2,2'-(1,3,4,5,7,8-hexafluoro-2,6-naphthalene-diylidene)bis-propanedinitrile, F6 TCNNQ) is demonstrated. Starting from an electron-depleted In2 O3 surface after annealing in oxygen, the deposition of [RuCp*mes]2 restores the accumulation layer as a result of electron transfer from the donor molecules to In2 O3 , as evidenced by the observation of (partially) filled conduction sub-bands near the Fermi level via angle-resolved photoemission spectroscopy, indicating the formation of a 2D electron gas due to the SEAL. In contrast, when F6 TCNNQ is deposited on a surface annealed without oxygen, the electron accumulation layer vanishes and an upward band bending is generated at the In2 O3 surface due to electron depletion by the acceptor molecules. Hence, further opportunities to expand the application of In2 O3 in electronic devices are revealed.

The Influence of the ITO Layers’ Thicknesses on Their Chosen Physical Surface Parameters

The paper presents the results concerning the influence of the thickness of the ITO and In2O3 layers deposited by the magnetron sputtering method on the physical parameters characterising their surface properties. The characterisation parameters were obtained by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Kelvin probe. The increase in the layers' thickness related to the time of their fabrication causes an increase in the surface roughness and the value of the work function, followed by a decrease in the concentration of elements and compounds in the near-surface area.

Electrospun Stacked Dual‐Channel Transistors with High Electron Mobility Using a Planar Heterojunction Architecture

AbstractThin‐film transistors based on metal oxide semiconductors have become a mainstream technology for application in driving low‐cost backplanes of active matrix liquid crystal displays. Although significant progress has been made in traditional marketable devices based on physical vapor deposition derived metal oxides, it has still been hindered by low yield and poor compatibility. Fortunately, developing solution‐based 1D nanofiber networks to act as the fundamental building blocks for transistor has proven to be a simpler, higher‐throughput approach. However, oxide transistors based on such princesses suffer from degraded carrier mobility and operational instability, preventing the ability of such devices from replacing present polycrystalline Si technologies. Herein, it is shown that double channel heterojunction transistors with high electron mobility (>40 cm2 V−1 s−1) and operational stability can be achieved from electrospun double channels composed of In2O3 and ZnO layers. Adjusting the stacking order and the stacking density of In2O3 and ZnO layers can effectively optimize the interface electron trap, leading to the formation of 2D electron gas and the reduction of stress‐induced instability. These findings further elucidate the significant advance of electrospinning‐derived double channel heterojunction transistors toward practical applications for future low‐cost and high‐performance electronics.

Optical characteristics with high accuracy of diluted Cr doped In2O3 thin films using spectroscopic ellipsometry for optoelectronic devices

Chemical reactions were used to create (In1-xCrx)2O3 powder with (x = 0, 2, 4, 6, 8 and 10 at.%), and an electron beam gun was used to evaporate thin films in a high vacuum. The impacts of Cr doping concentration on the structure and optics characteristics of the In2O3 layers were investigated. All Cr-doped In2O3 films had the cubic structure of In2O3 without secondary phases according to the X-ray diffraction findings. A study of the chemical makeup of each Cr-doped In2O3 compound revealed that they were all almost stoichiometric. To extract the optical characteristics and energy gap, a three-layer model simulated the experimental data of the spectroscopic ellipsometer. With increasing the Cr doping concentration, the optical band gap shifted the blue was seen. With increasing Cr content, the band gap in the (In1-xCrx)2O3 thin film was raised from 3.21 to 3.46 eV. Using the Murmann's exact equation, the refractive index and extinction coefficient that were obtained through spectroscopic ellipsometry could be utilized to fit the measured transmission data. As a function of Cr content, the change in structural parameters was be used to explain the change in the optical parameters. The (In1-xCrx)2O3 thin film are recommended for optoelectronic devices due to its tunability in the structural and optical properties.

(Invited, Digital Presentation) Photoactivated In2O3/GaN NW Sensors for Monitoring NO2 with High Sensitivity and Low Power

We report and discuss our results on the performance of our photoactivated In3O2/GaN NW sensors, for monitoring NO2 at various levels of relative humidity and operating power. A 1ppm sensitivity as high as 29% was demonstrated at operating power of 5 mW and relative humidity 40%.Nanostructure-based semiconductor gas sensors such as nanowires, nanotubes or nanorods have seen significant progress in recent years, owning to their large surface-to-volume ratio proprieties, which lead to considerably increased sensitivity and improve the time response to analyte gases. In particular, Gallium Nitride (GaN) nanostructure-based gas sensors have generated a lot of interest due to its unique combination of sensor “friendly” properties such as, direct bandgap, excellent carrier mobility, high heat capacity and high breakdown voltage. These properties combined with suitable surface engineering make GaN and GaN-based nanostructures an excellent candidate for portable gas sensors.In this work, Gallium Nitride (GaN) nanowire (NW)-based NO2 sensors, functionalized with either pure In2O3 or In2O3 covered with an evaporated Au nanolayer, were developed for low operating power and high sensitivity. An AlGaN buffer layer was first deposited on a Si substrate to minimize lattice mismatch and improve adhesion between the Si substrate and the GaN NWs. Then the GaN NWs were patterned by stepper lithography-assisted dry-etching, followed by Induced Coupled Plasma etching using a metal hard mask to protect the GaN NW. The nanowire width target ranged between 200-600nm. Subsequently, electrodes composed of Ti/Al/Ti/Au metal stacks were deposited on top of the GaN to form Ohmic contacts. A thin In2O3 layer metal oxide receptor was deposited on all devices, using RF magnetron sputtering on top of the exposed GaN NW and this was followed for a subgroup of devices by coating the In2O3 with an evaporated Au nanolayer. Finally, rapid thermal annealing (RTA) at 700 0C was performed to crystalize the receptor layers and improve the ohmic contact. The surface quality of the resulting sensors was inspected with the help of Scanning Electron Microscope (SEM) micrographs.Several devices of each group (In2O3 and In2O3/Au ) were wire bonded and mounted onto an array board chamber. The devices were biased under 5V DC. Photoconductivity measurements, humidity testing and NO2 gas testing (1ppm and 10ppm concentration) were conducted. The sensors were illuminated under constant UV LED illumination throughout the duration of the testing at two wavelengths, 265 nm and 365 nm and three irradiance levels, 5mW, 30mW and 60mW. In general, the In3O2 GaN NW sensors where characterized by low sensitivity levels, whereas the In3O2/Au GaN NW sensors achieved excellent sensitivity levels. Fig.1 shows typical dynamic responses to 1ppm NO2 of the In3O2/Au GaN NW sensors under illumination at 265 nm and 365 nm, respectively, and Fig.2 the response at various relative humidity (RH) levels. An increase in resistance upon exposure to NO2 is observed, confirming the oxidizing nature of the NO2 gas. At this NO2 concentration level, the highest response value (29%) was obtained under (5mW, 265 nm) illumination, whereas the sensitivity under (5mW, 365nm) illumination was lower. For (30mW, 265nm) illumination, the sensitivity was 23% and for (30mW, 365nm) illumination it dropped to 15%. This phenomenon has been observed in the past by other authors also, and although its origins are not yet understood unambiguously, it may be caused by a higher rate of phonon energy relaxation at the surface at higher wavelengths, thereby reducing the effectiveness of chemisorption at the surface. In conclusion, room-temperature low-power photoactivated In3O2/Au GaN NW sensors with excellent levels of sensitivity at elevated relative humidity were designed, fabricated and tested. Figure 1

Impact of annealing on the growth dynamics of indium sulphide buffer layers

Thin films of Indium sulphide are deposited on corning glass substrate by thermal evaporation at room temperature (300 K). The as-deposited films were annealed from 373 to 723 K under vacuum ∼1 × 10−3 mbar. An amorphous phase is obtained from 300 to 473 K; the polycrystalline β-In2S3 emerges at 523 K, and In2O3 is grown at 723 K. The intermediary phases of β-In2S3 and In2O3 are perceived from 573 to 673 K. A clear distinction between the morphology of β-In2S3 and In2O3 was observed in the micrographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The β-In2S3 dominated films provide absorption coefficient (α) from 18 to 25 × 104 cm−1, while α values of In2O3 layers lie within 1–5 × 104 cm−1. The bandgap (Eg) of β-In2S3 thin films is low (2.34 eV), and that of In2O3 is high (3.47 eV); however, the intermediary phases of β-In2S3 and In2O3 exhibit bandgap tunning from 2.30 to 3.14 eV. Moreover, the β-In2S3 shows the highest carrier concentration (Nd; 3.25 × 1018 cm−3), In2O3 provides the highest mobility (μ; 228 Cm2/V.s), and intermediary phases exhibit the lowest resistivity (ρ; 1.27 × 103 Ω/cm) within the existing forms. The thin films β-In2S3 phase grown at 523 and 573 K meet its stoichiometric ratio. In comparison, the In2O3 phase emerges under high oxygen and sulphur deficit conditions. The films are suitable for photo-conduction devices and in the buffer/window layer of PV solar cell design.

High Operation Frequency and Strain Tolerance of Fully Printed Oxide Thin Film Transistors and Circuits on PET Substrates.

The major limitations of solution-processed oxide electronics include high process temperatures and the absence of necessary strain tolerance that would be essential for flexible electronic applications. Here, a combination of low temperature (<100°C) curable indium oxide nanoparticle ink and a conductive silver nanoink, which are used to fabricate fully-printed narrow-channel thin film transistors (TFTs) on polyethylene terephthalate (PET) substrates, is proposed. The metal ink is printed onto the In2 O3 nanoparticulate channel to narrow the effective channel lengths down to the thickness of the In2 O3 layer and thereby obtain near-vertical transport across the semiconductor layer. The TFTs thus prepared show On/Off ratio ≈106 and simultaneous maximum current density of 172 µA µm-1 . Next, the depletion-load inverters fabricated on PET substrates demonstrate signal gain >200 and operation frequency >300kHz at low operation voltage of VDD = 2V. In addition, the near-vertical transport across the semiconductor layer is found to be largely strain tolerant with insignificant change in the TFT and inverter performance observed under bending fatigue tests performed down to a bending radius of 1.5mm, which translates to a strain value of 5%. The devices are also found to be robust against atmospheric exposure when remeasured after a month.

Monolithic bilayered In2O3 as an efficient interfacial material for high‐performance perovskite solar cells

AbstractCarrier recombination at the buried SnO2/perovskite interface limits the efficiency and stability of n‐i‐p‐structured perovskite solar cells (PSCs). Herein, we report an In2O3 interfacial layer with the distinctive structure of the monolithic compact/nanostructured bilayer. The partial hydrolysis nature of the In3+ ion enables the formation of nanorods on top of the compact In2O3 layer when spin‐coating the In(NO3)3 aqueous solution. This novel interfacial layer reduces the pinholes of the SnO2 film and increases the contact area between the perovskite and electron transport material. Therefore, PSCs with the incorporation of the interfacial layer demonstrate enhanced electron extraction and suppressed carrier recombination. Consequently, the champion device achieves a power conversion efficiency of 23.87% with a high fill factor of 82.14%. The optimized device also shows robust operational stability, retaining over 80% of the initial power conversion efficiency after working at the maximum power point for over 500 h under continuous one‐sun illumination.

Vertically stacked multilayer atomic-layer-deposited sub-1-nm In2O3 field-effect transistors with back-end-of-line compatibility

In this work, we demonstrate vertically stacked multilayer sub-1-nm In2O3 field-effect transistors (FETs) with surrounding gate in a back-end-of-line (BEOL) compatible low-temperature fabrication process. A typical bottom-gated single layer In2O3 FET with maximum on-state current (ION) of 890 μA/μm at VDS = 0.8 V and an on/off ratio over 106 is achieved with a channel length (Lch) of 100 nm. The effects of HfO2 capping and O2 annealing are systematically studied, which is critical to realizing the multilayer FETs. Each atomically thin In2O3 channel layer with a thickness (TIO) of 0.9 nm is realized by atomic layer deposition (ALD) at 225 °C. Multilayer FETs with a number of In2O3 layers up to 4 and 1.2 nm-thick HfO2 between each individual layer are fabricated. An enhancement of on-state current (ION) from 183 μA in a single layer In2O3 FET to 339 μA in a 4 layer device with an on/off ratio of 3.4 × 104 is achieved, demonstrating the key advantage of the multilayer FETs to improve the current. Several critical features, such as large-area growth, high uniformity, high reproducibility, ultrathin body, flexibility, and BEOL compatibility, have turned ALD In2O3 into a noteworthy candidate for next-generation oxide semiconductor channel materials.

High-bandwidth Si/In2O3 hybrid plasmonic waveguide modulator

A novel Si/In2O3 hybrid plasmonic waveguide modulator was experimentally realized by using an asymmetric directional coupler (ADC), which consists of a silicon photonic waveguide and a Si/In2O3 hybrid plasmonic waveguide. All the silicon cores are covered with a silica layer, above which there is a metal–oxide–semiconductor (MOS) capacitor consisting of the In2O3/HfO2/Au layers. The Au layer sitting on the top of the MOS capacitor works as the top-electrode, while the In2O3 thin film covers the sidewall and contacts with the Au bottom-electrode. When the bias voltage is not applied, light launched from the silicon photonic waveguide is weakly coupled into the Si/In2O3 hybrid plasmonic waveguide, and thus, one has a high transmission at the through port of the ADC. On the other hand, when the bias voltage is applied, the carrier density in the In2O3 layer is changed, which introduces some modification to the refractive index of the In2O3 thin film. As a result, light is strongly cross-coupled from the silicon photonic waveguide to a Si/In2O3 hybrid plasmonic waveguide, and one has low transmission at the through port. In this Letter, an ultra-compact Si/In2O3 hybrid plasmonic waveguide modulator is realized with a 3.5-μm-long ADC. In the experiments, the fabricated waveguide modulator works well and exhibits a high modulation bandwidth of &amp;gt;40 GHz for the first time.