Oxide Semiconductor Films Research Articles

(Invited) Development of Transparent Nanostructured Oxide Semiconductors for Electronic and Optoelectronic Devices

Wide band gap oxide semiconductor films offer optical transparency in the visible region of the electromagnetic spectrum. They are a technologically relevant class of materials applied in a wide range of commercial electronic and optoelectronic devices. The films of these materials exhibit high mechanical, chemical and thermal stability. Their electrical conductivity can be tuned from conducting to insulating range. Devices such as solar cells utilize their charge transport properties along with high visible light transmittance. Advent of nanostructured films of these materials has broadened their application scope. For example, such films can serve as high surface area supports for zero and two dimensional light absorbers in solar energy conversion devices. Electrochemical anodization has emerged as an effective technique to grow ordered nanostructured films of these materials on a variety of substrates. Anodically synthesized transparent films of highly ordered titania nanotube array is an example. Recently, our group has been successful in fabricating nanotube films of other wide bandgap oxide semiconductors using anodic oxidation. These materials have shown promising electronic and optoelectronic properties. This presentation provides the details of the fabrication of these materials and their performance as electrodes in solar photoelectrochemical devices for fuel generation and chemical sensors for medical diagnosis.

(Invited) The Tortuous History of Photoelectrochemistry and Photocatalysis after the Fujishima Discoveries

In this talk, I will attempt to chart the numerous twists and turns the twin fields of photoelectrochemistry and photocatalysis have undergone since the momentous discovery by Fujishima and Honda that anodic films of titania could split water into hydrogen and oxygen under sunlight. Interestingly, these authors did not discover this phenomenon, nor did they pioneer the fact that irradiated titania (or other oxide semiconductor) films could promote the photocatalytic degradation of environmental pollutants to mineralized products. There are also question marks on whether in the original Nature paper, these authors (and their junior collaborators) truly demonstrated that water was being split into hydrogen and oxygen. Instead, claims have been made that what they reported was a regenerative cell involving the generation and subsequent reduction of dioxygen instead of the photoinduced reduction of protons into hydrogen. (However, these authors did demonstrate, in a subsequent paper in the J. Electrochem. Soc., that hydrogen gas indeed was evolved in the correct stochiometric ratio with oxygen.) Nonetheless, it must be said that the Fujishima-Honda reports truly sparked intense interest in this solar conversion strategy and spawned a veritable, bonanza for the field, and indeed for the parent disciplines of photochemistry and electrochemistry. Other twists and turns that affected the evolution and growth of these twin fields including the discovery that most narrow bandgap semiconductors were photoelectrochemically unstable, and subsequent attempts to tackle this issue, will be discussed. Finally, the field of solar water splitting is truly at a pivotal point right now and its very future is murky. Avenues that may instead prove to be more profitable will be identified. Acknowledgements . The author thanks his numerous collaborators over the years. This work was primarily supported by the National Science Foundation UTA/NU Partnership for Research and Education in Materials (NSF DMR-2122128).

Influence of Treatment Time on the Synthesis of Copper Oxide Semiconductor Films by Cathode Cage Plasma Deposition

Influence of Treatment Time on the Synthesis of Copper Oxide Semiconductor Films by Cathode Cage Plasma Deposition

Thermal Dehydrogenation Impact on Positive Bias Stability of Amorphous InSnZnO Thin-Film Transistors.

Recently, the growing demand for amorphous oxide semiconductor thin-film transistors (AOS TFTs) with high mobility and good stability to implement ultrahigh-resolution displays has made tracking the role of hydrogen in oxide semiconductor films increasingly important. Hydrogen is an essential element that contributes significantly to the field effect mobility and bias stability characteristics of AOS TFTs. However, because hydrogen is the lightest atom and has high reactivity to metal and oxide materials, elucidating its impact on AOS thin films has been challenging. Therefore, in this study, we propose controlling the hydrogen quantities in amorphous InSnZnO (a-ITZO) thin films through thermal dehydrogenation to precisely reveal the hydrogen influences on the electrical characteristics of a-ITZO TFTs. The as-deposited device containing 15.69 × 1015 atoms/cm2 of hydrogen exhibited a relatively low saturation mobility of 18.1 cm2/V·s and poor positive bias stress stability. However, depending on the extent of thermal dehydrogenation, not only did the hydrogen quantity and interface defect density (DIT) decrease but also the conductivity and surface energy increased due to the rise in oxygen vacancies and hydroxyl groups in a-ITZO thin films. As a result, the a-ITZO TFT with a hydrogen amount of 4.828 × 1015 atoms/cm2 showed that the saturation mobility improved up to 36.8 cm2/V·s, and positive bias stress stability was remarkably enhanced. Hence, we report the ability to manage the hydrogen quantity with thermal dehydrogenation and demonstrate that high-performance a-ITZO TFTs can be realized when an appropriate hydrogen concentration is achieved.

Heteroepitaxial growth of Ga2O3 thin films on Al2O3(0001) by ion beam sputter deposition

Deposition of epitaxial oxide semiconductor films using physical vapor deposition methods requires a detailed understanding of the role of energetic particles to control and optimize the film properties. In the present study, Ga2O3 thin films are heteroepitaxially grown on Al2O3(0001) substrates using oxygen ion beam sputter deposition. The influence of the following relevant process parameters on the properties of the thin films is investigated: substrate temperature, oxygen background pressure, energy of primary ions, ion beam current, and sputtering geometry. The kinetic energy distributions of ions in the film-forming flux are measured using an energy-selective mass spectrometer, and the resulting films are characterized regarding crystalline structure, microstructure, surface roughness, mass density, and growth rate. The energetic impact of film-forming particles on the thin film structure is analyzed, and a noticeable decrease in crystalline quality is observed above the average energy of film-forming Ga+ ions around 40 eV for the films grown at a substrate temperature of 725 °C.

Grätzel type-solar cells sensitized with some Colombian's dyes

In the present work we want to show some progress related to the effects of two colombian's natural dyes in the sensitized solar cells (Grätzel type). The dyes used are achiote and blackberry, which are used to develop a photochemical process that mimics photosynthesis. The use of sensitizers in conjunction with nanocrystalline oxide semiconductor films (TiO2) permits to increase the absorption of sunlight. Raman spectroscopy technique has been used to characterize the achiote. They show that the samples have a strong fluorescence in the range between 640 and 800 nm, and this fluorescence is very sensitive to the laser power. After the construction of the solar cells, the efficiencies determined are around 0.13%, in the best of our cases.

Ultraviolet-sensitive and power-efficient oxide phototransistor enabled by nanometer-scale thickness engineering of InZnO semiconductor and gate bias modulation

Amorphous oxide semiconductor photodetectors (PDs) are promising ultrasensitive and power-efficient ultraviolet (UV) PDs because they generate low dark current in the dark and exhibit high photoresponse under UV irradiation owing to their superior UV absorption and photocarrier transport characteristics. Herein, we demonstrate UV-sensitive and power-efficient oxide phototransistors through the nanometer-scale engineering of oxide semiconductors and appropriate modulation of gate bias conditions. The dark current and photocurrent of an oxide phototransistor exhibit a trade-off relationship in terms of the thickness of the oxide semiconductor film. Ultrathin InZnO is disadvantageous for fabricating UV-sensitive PDs because of its low photoresponse. In contrast, excessively thick InZnO is disadvantageous for fabricating power-efficient UV PDs owing to its high dark current. However, the InZnO film with an optimal film thickness of 8 nm can simultaneously provide the advantages of both ultrathin and excessively thick cases owing to its low intrinsic carrier concentration and sufficient UV absorption depth. Consequently, an InZnO phototransistor with high UV-sensing performance (Smax = 1.25 × 106), low-power operation capability (Idark = ∼10−13A), and excellent repeatability is realized by using an 8-nm-thick InZnO semiconductor and applying appropriate gate bias modulation (constant gate bias for maximized photosensitivity and temporal positive bias pulse for persistence photocurrent elimination).

Doping of Indium Oxide Semiconductor Film Prepared Using an Environmentally Friendly Aqueous Solution Process with Sub-1% Molybdenum to Improve Device Performance and Stability

Doping of Indium Oxide Semiconductor Film Prepared Using an Environmentally Friendly Aqueous Solution Process with Sub-1% Molybdenum to Improve Device Performance and Stability

20.1: Invited Paper: Research on Oxide Thin Film Transistors for Wearable Sensors

With the rapid development of the Internet of Things, sensors as an important foundation in the era of smart interconnection, have a significant potential in the emerging fields of smart home, wearable devices, and smart mobile terminals. Flexible sensor has been attracting a great attention due to its portability, miniaturization and long endurance. The high consumption and signal crosstalk are urgent issues for the high‐integration sensing array. These issues could be effectively addressed by active‐matrix thin film transistors (TFT) backplane. In this work, the feasibility of oxide TFT for flexible sensor was discussed, in which high‐quality oxi de semiconductor films, oxide dielectric films, and printing Ag electrodes and wires were investigated, respectively. The device performance of flexible Si‐doped SnO2 TFT was optimized by modulating oxygen partial pressure, which could achieve a relative good electrical properties at room temperature. To implement low‐consumption application, high quality of high‐k ZrO2 dielectric film was investigated by solution‐processed method. The dielectric properties of ZrO2 film with the mircowave‐as sisted or deep ultraviolet irradiation‐assisted annealing process was similar to that of the thermal ann ealing process. The morphology and conductivity of Ag electrodes and wires printed by electrohydrodynamic (EHD) inkjet printing technology were studied. High conductivity of Ag electrodes and wires was achieved at a low curing temperature. These results imply that oxide TFT has a significant potential in the application of flexible sensor array.

Effects of Post-UV/Ozone Treatment on Electrical Characteristics of Solution-Processed Copper Oxide Thin-Film Transistors.

To realize oxide semiconductor-based complementary circuits and better transparent display applications, the electrical properties of p-type oxide semiconductors and the performance improvement of p-type oxide thin-film transistors (TFTs) are required. In this study, we report the effects of post-UV/ozone (O3) treatment on the structural and electrical characteristics of copper oxide (CuO) semiconductor films and the TFT performance. The CuO semiconductor films were fabricated using copper (II) acetate hydrate as a precursor material to solution processing and the UV/O3 treatment was performed as a post-treatment after the CuO film was fabricated. During the post-UV/O3 treatment for up to 13 min, the solution-processed CuO films exhibited no meaningful change in the surface morphology. On the other hand, analysis of the Raman and X-ray photoemission spectra of solution-processed CuO films revealed that the post-UV/O3 treatment induced compressive stress in the film and increased the composition concentration of Cu-O lattice bonding. In the post-UV/O3-treated CuO semiconductor layer, the Hall mobility increased significantly to approximately 280 cm2 V-1 s-1, and the conductivity increased to approximately 4.57 × 10-2 Ω-1 cm-1. Post-UV/O3-treated CuO TFTs also showed improved electrical properties compared to those of untreated CuO TFTs. The field-effect mobility of the post-UV/O3-treated CuO TFT increased to approximately 6.61 × 10-3 cm-2 V-1 s-1, and the on-off current ratio increased to approximately 3.51 × 103. These improvements in the electrical characteristics of CuO films and CuO TFTs can be understood through the suppression of weak bonding and structural defects between Cu and O bonds after post-UV/O3 treatment. The result demonstrates that the post-UV/O3 treatment can be a viable method to improve the performance of p-type oxide TFTs.

Hardware-Intrinsic Physical Unclonable Functions by Harnessing Nonlinear Conductance Variation in Oxide Semiconductor-Based Diode

With the advancement of the Internet of Things (IoT), numerous electronic devices are connected to each other and exchange a vast amount of data via the Internet. As the number of connected devices increases, security concerns have become more significant. As one of the potential solutions for security issues, hardware intrinsic physical unclonable functions (PUFs) are emerging semiconductor devices that exploit inherent randomness generated during the manufacturing process. The unclonable security key generated from PUF can address the inherent limitations of conventional electronic systems which depend solely on software. Although numerous PUFs based on the emerging memory devices requiring switching operations have been proposed, achieving hardware intrinsic PUF with low power consumption remains a key challenge. Here, we demonstrate that the process-induced nonlinear conductance variations of oxide semiconductor-based Schottky diodes provide a suitable source of entropy for the implementation of PUF without switching operation. Using a mild oxygen plasma treatment, the surface electron accumulation layer that forms naturally in oxide semiconductor film can be partially eliminated, resulting in a large variation of nonlinearity as an exotic entropy source. The mild plasma-treated Schottky diodes showed near ideal 50% average uniformity and uniqueness, as well as an ideal entropy value without the need for additional hardware area and power costs. These findings will pave the way for the development of hardware intrinsic PUFs to realize energy-efficient cryptographic hardware.

Formation and Properties of Thermistor Chips Based on Semiconductor 3D Metal Oxide Films Obtained by RF-Magnetron Sputtering

The formation of oxide semiconductor films of the (Mn,Co,Cu)3O4 type by radio frequency magnetron sputtering is presented. The conditions of deposition and subsequent heat treatment make it possible to obtain films with electrophysical characteristics close to those of the bulk ceramic materials used as a target for magnetron sputtering. Two variants of thermistor geometry were implemented. In the first case, the working layer of oxide semiconductor was deposited directly on the dielectric substrate (planar geometry), and in the second case on the layer with high electrical conductivity (Ni or Al) forming the inner electrode (layered geometry). The lower limit of the nominal resistance of the planar thermistor while maintaining high temperature nonlinearity is ~ 10 kΩ. The layered structure with the inner electrode makes it possible to reduce the lower limit of resistance up to ~ 50 Ω without losing the temperature nonlinearity of the thermistor. In addition, heat treatment above 450 °C or current self-heating with sufficient power output leads to the appearance of a pronounced voltage nonlinearity, which increases the thermal constant B of thermistors from 2400-3400 to 5000-5500 K. The fields of application of oxide-film structures for the correction of linear resistors and the implementation of integration approaches in the construction of linearized sensors are discussed.

Detection of H2S gas sensing performance of sol gel prepared metal oxide (In2O3, SnO2, Sn doped In2O3) thin films

Gas monitoring and control of hazardous and polluting gases (CO, H2S, CH4, H2, NH3, and alcohol) are required in industrial and laboratory applications where air quality must be regulated to protect public health, the environment, and security. Transparent conducting metal oxide semiconductors (TCO) have been shown to be extremely sensitive to both reducing and oxidising gases. They are caused by a lack of oxygen, also known as anion deficit. The present emphasis of scientific and technical endeavours is to improve the selectivity, stability, and practicability of response. Wide bandgap semiconducting oxides such as SnO2, In2O3 and Sn doped In2O3 have long been employed in gas sensing. The sensitivity of the gas sensor has increased as the thickness of the metal oxide semiconductor film or particle used to produce it has decreased. In the presence of reducible gases and adsorbed oxygen on the crystal surface, the conductivity is lowered by surface potential, when SnO2 is heated to high temperature, however, conductivity increases noticeably for In2O3 and indium tin oxide films. Indium oxide and tin oxide gas sensors detected H2S gas at working temperatures of 115 °C and 120 °C, respectively. Response and recovery times for indium oxide ranged from 10 s to 26 s and 34 s to 91 s, respectively, and for tin oxide from 3 s to 37 s and 82 s to 40 s. At 100 °C working temperature, ITO sensors with 10% tin concentration had the highest H2S sensitivity.

Comparison and Analysis of the third generation of the solar cells

Since the current energy crisis, the efficiency of using solar cell energy has become increasingly important. In order to get a high efficiency, new kinds of solar cells would be needed, which called the third generation of solar cells. This paper review three kinds of solar cells, including the perovskite solar cells, the quantum dots solar cells and the organic solar cells. Firstly, the structure of perovskite solar cells is composed of a FTO conducting glass, a TiO2 blocking layer, a TiO2 mesoporous layer, a perovskite layer, a HTM (Hole Transport Material) layer, and mental electrode. Then, I sum up the manufacture and the development of the perovskite solar cells. Secondly, this paper analysis the structure, manufacture, and development of quantum dots solar cells. The structure of quantum dots solar cells includes the transparent conducting oxide, wide bandgap oxide semiconductor film, quantum dot sensitizer, electrolyte, and counter electrode. The third one is the organic solar cells. The structure of the organic solar cells includes layer, cathode, anode, and transparent substrate. Finally, this paper reviews the merits and defects of each solar cells.

Active-ion-gated room temperature acetone gas sensing of ZnO nanowires array.

Reducing the high operation temperature of gas sensor to room temperature (RT) have attracted intense interests for its distinct preponderances, including energy-saving and super stability, which presents great prospects in commercial application. The exciting strategies for RT gas sensing, such as unique materials with activated surface or light activation, do not directly modulate the active ions for gas sensing, limiting the RT gas sensing performances. Here, an active-ion-gated strategy has been proposed for RT gas sensing with high performance and low power consumption, in which gas ions in triboelectric plasma are introduced into metal oxide semiconductor (MOS) film to act as both floating gate and active sensing ions. The active-ion-gated ZnO nanowires (NWs) array shows a sensitivity of 38.3% to 10ppm acetone gas at RT, and the maximum power consumption is only 4.5mW. At the same time, the gas sensor exhibits excellent selectivity to acetone. More importantly, the response (recovery) time of this sensor is as low as 11 s (25 s). It is found that OH-(H2O)4 ions in plasma are the key for realizing RT gas sensing ability, and an accompanied resistive switch is also observed. It is considered that the electron transfer between OH-(H2O)4 and ZnO NWs will forms a hydroxyl-like intermediate state (OH*) on the top of Zn2+, leading to the band bending of ZnO and activating the reactive O2 - ions on the oxygen vacancies. The active-ion-gated strategy proposed here present a novel exploration to achieving RT gas sensing performance of MOS by activating sensing properties at the scale of ions or atoms.

Metallic Nanoparticle-Doped Oxide Semiconductor Film for Bone Tumor Suppression and Bone Regeneration.

Bone implants with the photothermal effect are promising for the treatment of bone tumor defects. Noble metal-based photothermal nanoagents are widely studied for their stable photothermal effect, but they are expensive and difficult to directly grow on implant surfaces. In contrast, non-noble metal photothermal nanoagents are economical but unstable. Herein, to develop a stable and economical photothermal film on bone implants, a Ni nanoparticle-doped oxide semiconductor film was grown in situ on Nitinol via the reduction of Ni-Ti-layered double hydroxides. Ni nanoparticles remained stable in the NiTiO3 structure even when immersed in fluid for 1 month, and thus, the film presented a reliable photothermal effect under near-infrared light irradiation. The film also showed excellent in vitro and in vivo antitumor performance. Moreover, the nanostructure on the film allowed bone differentiation of mouse embryo cells (C3H10T1/2), and the released Ni ions supported the angiogenesis behavior of human vein endothelial cells. Bone implantation experiments further showed the enhancement of osteointegration of the modified Nitinol implant in vivo. This novel multifunctional Nitinol bone implant design offers a promising strategy for the therapy of bone tumor-related defects.

P‐1.1: Co‐sputtering‐deposited Hf‐doped ITO Thin Films for Thin Film Transistors Application

Oxide thin film transistors (TFTs) attract much attention in fields of advanced displays and low‐cost integrated circuits (ICs). In this work, hafnium doped InSnO (Hf‐ITO) thin films are deposited by co‐sputtering process, and are applied as the active layer to TFTs. Notably, the Hf‐ITO TFTs exhibit excellent device performance, preferable uniformity, and good gate‐bias‐stress stability. Major electrical parameters of the Hf‐ITO TFTs include a field‐effect mobility (μFE) of 7.46 cm2V−1s−1, a turn‐on voltage (VON) of 1.10 V, a sub‐threshold swing (SS) of 341.18 mV/decade, and an on/off state current ratio (ION/IOFF) over 105. Our work proposes a novel method for developing high‐mobility semiconductor oxide films and oxide TFTs.

A simulation and experimental study of the parasitic reaction and flow field in the growth of metal–oxide films

Metal–organic chemical vapor deposition (MOCVD) is an important method for growing metal–oxide semiconductor films. However, owing to problems associated with gas-phase parasitic reactions and wall deposition, this method achieves low growth efficiency and affects the film quality. Computational fluid dynamics (CFD) has been widely used in MOCVD research and can be employed to investigate the flow field and the chemical vapor deposition (CVD) process in the reactor. In this study, considering the growth of zinc oxide and indium oxide as examples, a four-step reaction mechanism is proposed based on a combination of the multi-step reaction mechanism and experimental results. The effect of chemical reactions on the film growth rate is studied based on the Arrhenius plot and experimental results. A new flow stability map is proposed, and the flow field stability under different pressures is investigated to explore the influence of the flow field on the film growth rate. Results show that the deposition rate is influenced by both the gas-phase parasitic reactions and the effect of the flow field on the source component distribution. Furthermore, the causes and factors influencing sidewall deposition are revealed.

Ternary-Oxides CuWO4/BiVO4/FeCoOx Films for Photoelectrochemical Water Oxidation: Insights into the Photoinduced Charge Transfer Pathway

Photoelectrochemical (PEC) water oxidation using semiconductor oxide films as a working electrode is an essential approach for investigating the effective utilization of sunlight and the production of green fuel. Herein, we report a ternary-oxides-based CuWO4/BiVO4/FeCoOx film deposited entirely by RF-magnetron sputtering using homemade ceramic targets. Our CuWO4/BiVO4 photoanode exhibits a significant photocurrent density of 0.82 mA/cm² at 1.23 V vs. RHE under AM 1.5G illumination, corresponding to a record > 380% increase to that of pure CuWO4 photoanode. To further boost the PEC performance, we deposited an ultrathin layer of amorphous FeCoOx cocatalyst, resulting in a triple CuWO4/BiVO4/FeCoOx heterojunction with a significant reduction in onset potential and a 500% increase in photocurrent density of pure CuWO4. Experimental studies and numeric computations were used to provide insights into the photoinduced charge carrier pathway across heterojunctions. Our results reveal noticeable interface potential barriers for charge carriers at the CuWO4/BiVO4 heterojunction, potentially lowering PEC efficiency without external potentials. Conversely, the deposition of the FeCoOx ultrathin layer over the CuWO4/BiVO4 heterojunction induces a - junction on the BiVO4/FeCoOx interface, which, when combined with the abundant FeCoOx oxygen vacancies, results in improved charge separation and transport, as well as enhanced photoelectrochemical stability. Our study provides a feasible strategy for producing photocatalytic heterojunctions systems and novel tools for investigating interface effects on photoinduced charge carrier pathways for PEC water splitting.

Viable strategy to minimize trap states of patterned oxide thin films for both exceptional electrical performance and uniformity in sol–gel processed transistors

• Sustainable water etchant-based photopatterning method is proposed for sol–gel oxide films. • Patterning process remarkablely minimize trap states of dielectric and semiconductor oxide films. • Frequency-stable capacitors with low leakage current are fabricated by using low-defect AlO x. • Low-defect InO x based TFTs with exceptional electrical performance and uniformity are fabricated. • 3-V operating high-performance TFTs are fabricated at a low processing temperature of 250 °C. A sustainable water etchant-based photopatterning method is proposed to achieve simultaneous oxide film patterning and remarkably minimize trap states of dielectric and semiconductor oxide films. By exquisitely controlling each processing parameter, well-defined aluminum oxide (AlO x ) dielectric and indium oxide (InO x ) semiconductor patterns are formed, despite using acid-free pure water etchant. The water etchant not only dissolves the nonultraviolet-irradiated regions but also promotes an effective hydrolysis reaction of irradiated regions, thereby forming low-defect oxide patterns. As a result, frequency-stable AlO x capacitors with low leakage current and high-performance bias-stable InO x TFTs with low activation energy are fabricated. In particular, photopatterned enhancement-mode InO x TFTs exhibit remarkably improved electrical properties, stability, and uniformity—15-fold higher saturation mobility and remarkably low coefficient of variation of 12.04 cm 2 V −1 s −1 and 25.26%, respectively— compared with nonpatterned TFTs. With the proposed method, 3-V operating high-performance InO x /AlO x TFTs are successfully fabricated at a low processing temperature of 250 °C.