Oxide Semiconductor Thin Film Research Articles

P‐17: Development of Vertical Oxide Channel Thin Film Transistor Based on Hard‐Mask Etching

Avertical oxide semiconductor thin film transistor (VTFT) with channel lengthof 0.4 μm wasdeveloped in our work. This VTFT has a small footprint, which isconducive to achieving higher resolutiom. In this work, we produced a VTFT by usinga hardmask etching process and designed different vertical structures, such asslope, hole, etc. The device achieved an on‐state current of 20.6 μA (normalized with width) and an off‐state current below 1 pA.

Deep-Submicron Channel Length Oxide Semiconductor Thin-Film Transistors Enabled by Self-Aligned Nanogap Lithography

Deep-Submicron Channel Length Oxide Semiconductor Thin-Film Transistors Enabled by Self-Aligned Nanogap Lithography

Research on correlation between metal oxide semiconductor target and magnetron sputtered film based on TFT application

The research on the intrinsic relationship between target quality and TFT (thin film transistor) performance is not perfect for magnetron sputtering processes. The systematic analysis of target-film-device still needs to be improved. This paper studied the internal relationship between metal oxide semiconductor targets, thin films, and TFT devices for the deterioration problem of device performance caused by the failure of the aging target. The experimental results showed that the target surface with a long cumulative sputtering time had apparent macroscopic concave, related to the electromagnetic field distribution. The concave region was the primary source of thin film composition, so the research object of this work was mainly the concave region. A multi-oxide target was used in this work, and its selective sputtering phenomenon was serious, mainly reflected in the sputtering rate of In2O3 grains with higher electrical conductivity than other components. There were many failure sites on the surface of the target, including nodules, holes, coating layers, and cracks. The failure sites would hinder the normal sputtering process and eventually form a vicious circle, failing the target. Due to the decline of target quality, sputtering particles would be in a state of insufficient kinetic energy, resulting in particle agglomeration, element segregation, weak M-O (metal-oxide) bonds, loose accumulation, and surface or block defects. Ultimately, the TFT performance with the aging target showed lower mobility, larger subthreshold swing, increased off-state current, and poorer stability. Clarifying the relationship between target quality and device performance is beneficial for the development of electronic devices.

Nanostructured Oxide (SnO2, FTO) Thin Films for Energy Harvesting: A Significant Increase in Thermoelectric Power at Low Temperature.

Previous studies have shown that undoped and doped SnO2 thin films have better optical and electrical properties. This study aims to investigate the thermoelectric properties of two distinct semiconducting oxide thin films, namely SnO2 and F-doped SnO2 (FTO), by the nebulizer spray pyrolysis technique. An X-ray diffraction study reveals that the synthesized films exhibit a tetragonal structure with the (200) preferred orientation. The film structural quality increases from SnO2 to FTO due to the substitution of F- ions into the host lattice. The film thickness increases from 530 nm for SnO2 to 650 nm for FTO films. Room-temperature electrical resistivity decreases from (8.96 ± 0.02) × 10-2 Ω·cm to (4.64 ± 0.01) × 10-3 Ω·cm for the SnO2 and FTO thin films, respectively. This is due to the increase in the carrier density of the films, (2.92 ± 0.02) × 1019 cm-3 (SnO2) and (1.63 ± 0.03) × 1020 cm-3 (FTO), caused by anionic substitution. It is confirmed that varying the temperature (K) enhances the electron transport properties. The obtained Seebeck coefficient (S) increases as the temperature is increased, up to 360 K. The synthesized films exhibit the S value of -234 ± 3 μV/K (SnO2) and -204 ± 3 μV/K (FTO) at 360 K. The estimated power factor (PF) drastically increases from ~70 (μW/m·K2) to ~900 (μW/m·K2) for the SnO2 and FTO film, respectively.

High Reliability Tungsten-Doped Indium Zinc Oxide Thin Film Transistors for Display Applications

Recently, flat panel display technologies are based on amorphous silicon (a-Si), polycrystalline silicon (poly-Si) or amorphous oxide semiconductor (AOS) thin film transistors (TFTs) technology. In order to reach higher performance for ultra-high resolution display applications, the material selection for the channel layer is vital. AOS TFTs drawn lots of attention because of its advantages such as low leakage current, high driving current and high uniformity [1,3]. In this work, we presented a novel amorphous oxide semiconductor (AOS) material of gallium-free a-InWZnO thin film transistors (IWZO TFTs) which is very promising to be applied for ultra-high resolution display technology. Experiment In this work, we demonstrated the structure of a-IWZO TFTs processes. Figure 1 shows the schematic of the TFT cross-section. After growing a 550 nm thermal oxide layer as buffer layer, a 25-nm-thick of molybdenum was deposited by DC-sputter as the bottom gate electrode. A 10-nm-HfO2 was deposited by plasma-enhanced atomic layer deposition (PEALD) system as high-κ gate dielectric (GI). Then, post deposition annealing (PDA) was carried out to enhance the quality of the insulator layer. Next, an ultra-thin body a-IWZO was deposited by RF-sputter as channel layer. Finally, source and drain were defined by lift-off process and the gate contact via was etched by dry etching to finish the device fabrication. Result and Discussion Figure 1(b) shows the negative gate bias stress (NGBS) transfer curve (ID-VG) of a-IWZO TFTs with passivation layer. The experimental results have shown that passivation layer could keep the back channel of IWZO channel from exposing to oxygen and hydrogen from the atmosphere. Without the passivation layer, the back channel would contact moisture leading the diffused hydrogen atoms to fill oxygen vacancy sites and de-trap free carriers, causing the VTH shifts negatively. The ultra-thin a-IWZO TFTs with passivation layer exhibited a low subthreshold swing (S.S.) of 89.7 mV/dec, high on/off current ratio (ION/IOFF) of 2.1×107 and small threshold voltage shift (ΔVth) of -0.097 V during NGBS of -2MV/cm with 2000s. To sum up, the passivation layer could enhance the a-IWZO TFTs reliability. Reference [1] Kamiya, H. Hosono, NPG Asia Mater., vol. 2, pp. 15, 2010.[2] Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, nature, vol. 432, no. 7016, pp. 488-492, 2004.[3] Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019. Figure 1

Energy-Band Engineering By Remote Doping of Self-Assembled Monolayers Leads to High-Performance Igzo/P-Si Heterostructure Photodetectors

Advancements in emerging technologies, such as autonomous driving, artificial intelligence, medical imaging, and augmented reality, have increased the demand for high-resolution image sensors to transmit further accurate color information. To meet the performance requirements of these applications, several research have been accelerating towards the utilization of emerging low-dimensional semiconductor materials, such as metal oxides, transition metal dichalcogenides, perovskites, and other organic materials.Among them, metal oxide semiconductors (MOSs) are potential candidates for developing high-performance photodetectors. It can be synthesized over large areas using a simple/low-temperature process and are compatible with conventional fabrication equipment. However, MOS-based photodetectors still have several limitations, 1) the presence of charge traps and operational instability on the oxide surface, which degrade photodetection performance, and 2) the absence of an appropriate doping technique for MOS has blocked to improve photodetection performance via materials characteristic modification method.In this study, we present a strategy to overcome these limitations and significantly enhance the performance of IGZO, which is representative of oxide semiconductor thin film, based photodetector with high operation stability and sustainability under ambient atmospheres. We utilized energy-band engineering through an octadecylphosphonic acid (ODPA) self-assembled-monolayer (SAM)-based doping treatment to enhance the photoelectric characteristics of IGZO/p-Si hetero-interfaced devices (ISH). The ODPA consists of a head group of the hydroxyl group, which forms the self-assembled covalent bond formation of R–P–O–substrate. Combining the ODPA SAM with the oxide surface of IGZO provided carrier concentration control based on their a dipole effect, and remain the performance and functionality through the surface encapsulation. As a result, under a light-emitting diode (LED) wavelength with an intensity of 3.9 mW, the proposed device exhibited remarkable photo-switching current ratio of 4.33 × 103 A/A and negative differential resistance (NDR) phenomenon. Espacially, the dark current of the ODPA treated ISH is decreased about 10 times lower than as-fabricated ISH, which shows the possibility of signal noise minimization. These performance improvement is expected to be derived from band properties modulation through IGZO layer annealing and ODPA doping. To clarify the doping effect of each treatment, we characterized the ODPA self-assembled monolayer using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM) to provide comprehensive analysis of the heterointerface effects. We also characterized the electrical properties of IGZO thin-film transistors (TFTs) based on variations of the annealing temperature to clarify the ODPA doping effect.We evaluated 156 ODPA-treated IGZO/p-Si heterostructure photodetectors, which were scaled for fabrication on a 4 inch wafer. The devices exhibited a 100% yield, and uniform current behavior in the dark state (0.20 ± 0.06 nA) and light state (0.87 ± 0.15 µA), owing to an evenly deposited IGZO layer and a simple-to-treat ODPA doping scheme. Furthermore, consecutive sweeps of 20,000 cycles verified excellent cycle-to-cycle endurance, resulting in highly robust photoelectric behaviors without operational failure. Additionally, the performance of the ODPA-treated, IGZO/p-Si heterostructure photodetector remained unchanged for 237 days without degradation under atmospheric exposure (relative humidity (RH) = 37–53 % and 20.6–23.1 °C). Acknowledgements This research was supported by funding supports from the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2020R1A2C1101647) and Korea government (MEST) (NRF-2017R1A2B3011222). Figure 1

Enhance hydrogen sulfide (H2S) gas sensor based on metal oxide semiconductor (NiO) thin films

Enhance hydrogen sulfide (H2S) gas sensor based on metal oxide semiconductor (NiO) thin films

Machine Learning Driven Channel Thickness Optimization in Dual-Layer Oxide Thin-Film Transistors for Advanced Electrical Performance.

Machine learning (ML) provides temporal advantage and performance improvement in practical electronic device design by adaptive learning. Herein, Bayesian optimization (BO) is successfully applied to the design of optimal dual-layer oxide semiconductor thin film transistors (OS TFTs). This approach effectively manages the complex correlation and interdependency between two oxide semiconductor layers, resulting in the efficient design of experiment (DoE) and reducing the trial-and-error. Considering field effect mobility (𝜇) and threshold voltage (Vth ) simultaneously, the dual-layer structure designed by the BO model allows to produce OS TFTs with remarkable electrical performance while significantly saving an amount of experimental trial (only 15 data sets are required). The optimized dual-layer OS TFTs achieve the enhanced field effect mobility of 36.1cm2 V-1 s-1 and show good stability under bias stress with negligible difference in its threshold voltage compared to conventional IGZO TFTs. Moreover, the BO algorithm is successfully customized to the individual preferences by applying the weight factors assigned to both field effect mobility (𝜇) and threshold voltage (Vth ).

Spray pyrolyzed lead oxide films for Schottky junction solar cells

In this paper, we report the fabrication of Schottky solar cell based on spray pyrolysed lead oxide semiconductor thin films. The non-linear junction were created by using high work function metal alloy of Au–Pd with hydrogen treated undoped and Indium doped lead oxide films. The output of Schottky device with different thickness of absorber layer is presented. The electrical parameters of the device are ascertained from the I–V measurements. The device with 2 μm thickness of absorber layer gives a Voc value of 148 mV and Jsc value of 0.21 mA/cm2. The high ideality factor obtained for all varying thickness is attributed to both the surface states generated under illumination and non-homogeneous interface due to the rough surfaces of spray pyrolysed films. In case of Indium doped lead oxide films, an enhanced Voc value of 570 mV and Jsc of 0.11 mA/cm2 is observed. The pristine films and doped films have been characterized by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy.

Low-Voltage Operated High DC Gain Amplification Stage Based on Large-Area Manufacturable Amorphous Oxide Semiconductor Thin-Film Transistor

The industry-standard amorphous metal–oxide–semiconductor (AOS) thin-film transistor (TFT) technology is demonstrated for making low-voltage high intrinsic gain devices. It is revealed by the technology computer-aided design (TCAD) simulation that, without need of making Schottky barrier contacts, large output resistance and high intrinsic gain can be achieved in a subthreshold regime for AOS TFTs. It is further proved by the measurement results with the fabricated AOS TFT from a Gen-4.5 manufacturing line. A simple single-stage zero- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\text{GS}}$</tex-math> </inline-formula> load amplifier is implemented as a proof of concept, achieving a voltage gain larger than 50 for weak signal detection at a supply voltage of 5 V.

Simultaneous Extraction of Mobility Enhancement Factor and Threshold Voltage With Parasitic Resistances in Amorphous Oxide Semiconductor Thin-Film Transistors

This study presents a technique for simultaneous and consistent extraction of the mobility enhancement factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma$</tex-math> </inline-formula> ) and the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{T}}$</tex-math> </inline-formula> ) with parasitic source and drain resistances ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{S}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{D}}$</tex-math> </inline-formula> ) in amorphous oxide semiconductor (AOS) thin film transistors (TFTs). This technique allows for the extraction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{S}}$</tex-math> </inline-formula> from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{D}}$</tex-math> </inline-formula> as well as the accurate extraction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{T}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $</tex-math> </inline-formula> with only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}$</tex-math> </inline-formula> characteristics of the saturation operation in a single AOS TFT. The proposed technique was applied to amorphous indium–gallium–zinc-oxide (a-IGZO) TFTs with various structures. For intentional asymmetry, we confirmed the consistency with an external resistor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\text{ext}} = \text{10}$</tex-math> </inline-formula> , 20, 30 k <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> ). Extracted parameters ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{S}}$</tex-math> </inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\textit{D}}$</tex-math> </inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{T}}$</tex-math> </inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma$</tex-math> </inline-formula> ) by the proposed method were compared with parameters extracted by other methods for verification. Furthermore, the drain current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D}}$</tex-math> </inline-formula> ) was well reproduced using the extracted parameters regardless of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{R}_{\text{ext}}$</tex-math> </inline-formula> .

PdRh-Sensitized Iron Oxide Ultrathin Film Sensors and Mechanistic Investigation by Operando TEM and DFT Calculation.

Metal oxide semiconductor (MOS) thin films are of critical importance to both fundamental research and practical applications of gas sensors. Herein, a high-performance H2 sensor based on palladium (Pd) and rhodium (Rh) co-functionalized Fe2 O3 films with an ultrathin thickness of 8.9nm deposited by using atomic layer deposition is reported. The sensor delivers an exceptional response of 105.9 toward 10ppm H2 at 230 °C, as well as high selectivity, immunity to humidity, and low detection limit (43 ppb), which are superior to the reported MOS sensors. Importantly, the Fe2 O3 film sensor under dynamic H2 detection is for the first time observed by operando transmission electron microscopy, which provides deterministic evidence for structure evolution of MOS during sensing reactions. To further reveal the sensing mechanism, density functional theory calculations are performed to elucidate the sensitization effect of PdRh catalysts. Mechanistic studies suggest that Pd promotes the adsorption and dissociation of H2 to generate PdHx , while Rh promotes the dissociation of oxygen adsorbed on the surface, thereby jointly promoting the redox reactions on the films. A wireless H2 detection system is also successfully demonstrated using the thin film sensors, certifying a great potential of the strategy to practical sensors.

Plasma processing technique by combination of plasma-assisted reactive sputtering and plasma annealing for uniform electrical characteristics of InGaZnO thin film transistors formed on large-area substrates

The homogeneous formation of high-mobility oxide semiconductor thin films over large areas at low temperatures was accomplished by optimizing both the film formation process and the low-temperature post-processing via plasma annealing. Increasing the substrate-to-target distance (D ST) and the applied target voltage was found to produce more uniform deposition. The results of the field-effect mobility distributions of IGZO TFTs processed using plasma annealing were founded that plasma annealing generated essentially uniform distributions with μ FE values in the range of 32–35 cm2 V−1 s−1.

Characterization of Zinc Oxide Semiconductor Thin Film Treated with Cold Plasma

In this study, the photovoltaic properties of zinc oxides are investigated. Different stoichiometries of zinc oxide can be made using vacuum deposition. Thermally evaporated zinc produces thin films of ZnO composed of orthorhombic and tetragonal phases that define the material's characteristics and performance. On-thermal plasma has removed a very thin layer from the surface of the thin film, known as non-thermal plasma, and made a surface cleanup. Measurements of the Atomic Force Microscope (AFM) show that the value of the granular volume rate increases when the duration of exposure to non-heat plasma increases. Measurements of the Atomic Force Microscope (AFM) show that there is an increase in thin film surface roughness values (Roughness, Sq), as well as the square root of the average roughness of the thin film surface (RMS), and this increase in roughness appears as the duration of exposure to non-thermal plasma increases.

Photoresponse of solution-processed transparent heterojunction ultraviolet photodetectors composed of n-type ZTO and p-type NiO-based semiconductor thin films

The n-type zinc-tin oxide (ZTO) and p-type nickel oxide (NiO) semiconductor thin films were prepared by the sol-gel spin coating process. The influence of 4 at% Mg and Cu doping on the microstructural, optical, and electrical characteristics of NiO thin films and physical properties of ZTO thin film were investigated. In addition, bi-layered ZTO/NiO thin films were grown onto Corning glasses to develop a visible light transparent p-n heterojunction ultraviolet (UV) photodetector. Mg doping slightly enhances the visible transparency and enlarges the optical bandgap energy, while Cu doping decreases the visible transparency and narrows the optical bandgap energy. The electrical properties of NiO sol-gel thin films were improved through Mg and Cu doping. According to the current-voltage (I–V) characteristic curves, the n-ZTO/p-NiO:Mg photodetector had the highest rectification ratio of 11.7 and on-to-off current ratio of 18.3 at 5 V bias. Under UV illumination, the three kinds of devices all exhibited a self-powered nature, while the Mg- and Cu-doped NiO devices had better photoresponse characteristics than the undoped NiO device. It was found that the Mg-doped NiO devices displayed the best photoconductivity gain and sensitivity, and acceptable response speed and responsivity, with applied reverse bias of 1 V.

Copper iodide and oxide semiconductor thin films patterned by spray-spin coating for fabricating complementary inverters: Improving stability with passivation layers

Recently, copper iodide (CuI) has been studied as a solution-processed p-type semiconductor owing to its high hole mobility and low-temperature processability. With the development of the field in this solution-processed inorganic semiconductor, it has become increasingly necessary to integrate the p-type thin-film transistors (TFTs) into a complementary inverter using a simple solution-based patterning method. However, compared to the n-type counterpart, it remains a challenge to pattern the p-type inorganic TFTs while maintaining reliable performances. In this study, Zn-doped CuI (Zn:CuI) were patterned in a simple manner by combining spin and spray coating, namely “spray-spin coating,” to fabricate p-type TFTs. The device stability of the spray-spin-coated Zn:CuI TFTs was ensured by treating hydrophobic fluoropolymer, CYTOP, as a passivation layer. Owing to the blocking of oxygen penetration at the CYTOP layer, which was confirmed by the chemical binding energy states of the Zn:CuI thin film, the resulting devices exhibited enhanced electrical characteristics while maintaining low off-state current and normal threshold voltage. Finally, via spray-spin coating, complementary inverters comprising n-type In2O3/ZnO bilayer and p-type Zn:CuI semiconductors were successfully fabricated on a single wafer, demonstrating a robust switching operation.

9‐2: Oxide TFT behavior Under X‐Ray Irradiation in DXD Backplane

Recently, the digital X‐ray detector (DXD) technology requires high quality and high frame rate dynamic images, so efforts are being made to apply an oxide semiconductor (OS) thin film transistor (TFT) to the DXD backplane as a switching device instead of an amorphous Si (a‐Si) TFT. In order for the OS TFT to be used as a switching device of the X‐ray detector, it is necessary to study about the degradation parameters of the OS TFT under X‐ray irradiation. We confirmed that the threshold voltage (Vth) of the InGaZnO (IGZO) TFTs shifted negatively without s‐factor degradation according to X‐ray exposure. To understand these characteristics, we evaluated the X‐ray degradation characteristics of various methods.

Hole-injection role of solution-processed thermally treated VOx thin films in Si nanowire-based solar cells

We have studied the hole-injection workability of dopant-free vanadium oxide (VOx) semiconductor thin films. Solution-processable VOx films were annealed in different atmospheres at 450 ˚C. X-ray diffraction showed that different crystal structures of V2O5, VO2 (M) and VO2 (B) were obtained after annealing in oxygen, nitrogen and under vacuum respectively. Gap states that originated from oxygen deficiencies located inside the band gap of the annealed VOx were demonstrated using X-ray photoelectron spectroscopy. These VOx thin films act effectively as transparent hole-injection layers owing to their high work function, wide band gap, and presence of oxygen deficiencies. The different ambient annealed VOx films were employed in Si nanowire (SiNW)-based solar cells. The vacuum-annealed oxide film VO2–x (B) showed the best hole-injection ability. SiNWs/VOx solar cells are noticeably more stable than SiNWs/PEDOT:PSS hybrid solar cells, which decay swiftly under ambient conditions unless encapsulation is provided. The utilization of VOx films to act as hole-injection layers opens a pathway toward the development of cheap and durable electronics and optoelectronics devices.

Drain Current Drop in Oxide Semiconductor Thin-Film Transistors: The Mechanisms and a Solution

The reliability of amorphous oxide semiconductor thin-film transistors (AOS-TFTs) is vital for high-definition displays and functional electronic devices. However, drain current drop (DCD) degradation has been commonly observed in the output characteristics of thin-film transistors (TFTs) with channel lengths of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L} &lt; 10 \mu \text{m}$ </tex-math></inline-formula> . Here, we show that DCD is a reversible process that is closely related to reduced metal-oxygen bonds. Based on device theory and simulations, we propose that the DCD effect is mainly caused by hot carriers, whose velocities are inversely proportional to the drain depletion width. Therefore, DCD failure could be alleviated simply by using the drain-offset structure. Experiments show that drain-offset TFTs improve DCD critical voltages (by ~130%) without sacrificing the ON-/ OFF-ratio. These studies provide theoretical and experimental approaches to effectively suppress DCD.

Experimental and theoretical study of hole scattering in RF sputtered p-type Cu2O thin films

One of the key materials of interest for p-type oxide semiconductor thin film electronics is cuprous oxide (Cu2O), due to its relatively high hole mobility. In this work, we use experiments, analytical models, and density functional theory calculations to study the scattering mechanisms that determine Hall mobility in two Cu2O samples. First, we examine a polycrystalline Cu2O thin film deposited by RF magnetron sputtering, and second, a single-crystalline Cu2O bulk substrate. Temperature-dependent Hall measurements indicate that neutral impurity and grain boundary scattering are dominant for the polycrystalline Cu2O thin film, while phonon scattering is dominant for single-crystalline Cu2O. Our first-principles calculations show that the room-temperature intrinsic hole mobility of Cu2O is 106 cm2 V−1 s−1, indicating the great promise of the material for p-type electronic devices. This intrinsic mobility is limited by phonon scattering, with the most dominant scattering modes having phonon energies of 88.4 and 17.1 meV. These results indicate that the key pathways to increase the hole mobility in Cu2O thin films are by reducing the impurity concentration and by increasing grain size. Our work thus sets the stage for the future development of high performance Cu2O-based p-type thin film transistors.