Engineering Of Semiconductors Research Articles

Band Gap Engineering of Semiconductors and Ceramics by Severe Plastic Deformation for Solar Energy Harvesting

Band Gap Engineering of Semiconductors and Ceramics by Severe Plastic Deformation for Solar Energy Harvesting

Interfacial charge trap engineering of organic semiconductors using reactive oxygen plasma for enhanced performance in phototransistor memory

Significant advancements have been observed in organic photonic field-effect transistors, primarily attributed to the swift evolution of conjugated materials. In this study, plasma oxidation is utilized as a surface modification strategy on a series of quinacridones (QA) based molecules to further exploit the performance of conjugated materials. Accordingly, alkylated QA is incorporated as a memory layer into the photonic field-effect transistor memory devices, with pentacene serving as the transport layer. The study aims to elucidate the correlation between functionalized interfaces and charge storage capacity. The findings indicate that plasma oxidation can elicit charge storage effects due to the formation of tertiary amine species and morphological modifications. The alkylated QA with an optimal chain length, subjected to a 10-s plasma oxidation process, demonstrates remarkable memory ratios reaching as high as 104. Additionally, the retention capabilities of these devices remain approximately 104 after a duration of 10,000 s, signifying substantial durability. These findings underscore the efficacy of plasma oxidation as a significant method for enhancing the operational performance of photonic field-effect transistor memory devices.

Visible-Light-Driven Oxidation of Benzene to Phenol with O2 over Photoinduced Oxygen-Vacancy-Rich WO3.

Direct photocatalytic conversion of benzene to phenol with molecular oxygen (O2) is a green alternative to the traditional synthesis. The key is to find an effective photocatalyst to do the trick. Defect engineering of semiconductors with oxygen vacancies (OVs) is an emerging strategy for catalyst fabrication. OVs can trap electrons to promote charge separation and serving as adsorption sites for O2 activation. However, the randomly distribution of OVs on the semiconductor surface often results in mismatching the charge carrier dynamics under irradiation, thus failing to fulfill the unique advantages of OVs for photoredox functions. Herein, we demonstrate that abundant OVs can be facilely generated and precisely located adjacent to the reductive sites on reducible oxide semiconductors such as tungsten oxide (WO3) via a simple photochemistry strategy. Such photoinduced OVs are well suited for photocatalytic benzene oxidation with O2 as they readily capture photogenerated electrons from the reductive sites of WO3 to activate adsorbed O2. The oxygen-isotope-labeling experiments further confirm that the OVs also facilitate the integration of oxygen atoms from O2 into phenol, revealing in detail the pathway for photocatalytic benzene hydroxylation. This study demonstrates that the photochemistry approach is an appealing strategy for the synthesis of high-performance OVs-rich photocatalysts for solar-induced chemical conversion.

Visible‐Light‐Driven Oxidation of Benzene to Phenol with O2 over Photoinduced Oxygen‐Vacancy‐Rich WO3

AbstractDirect photocatalytic conversion of benzene to phenol with molecular oxygen (O2) is a green alternative to the traditional synthesis. The key is to find an effective photocatalyst to do the trick. Defect engineering of semiconductors with oxygen vacancies (OVs) is an emerging strategy for catalyst fabrication. OVs can trap electrons to promote charge separation and serving as adsorption sites for O2 activation. However, the randomly distribution of OVs on the semiconductor surface often results in mismatching the charge carrier dynamics under irradiation, thus failing to fulfill the unique advantages of OVs for photoredox functions. Herein, we demonstrate that abundant OVs can be facilely generated and precisely located adjacent to the reductive sites on reducible oxide semiconductors such as tungsten oxide (WO3) via a simple photochemistry strategy. Such photoinduced OVs are well suited for photocatalytic benzene oxidation with O2 as they readily capture photogenerated electrons from the reductive sites of WO3 to activate adsorbed O2. The oxygen‐isotope‐labeling experiments further confirm that the OVs also facilitate the integration of oxygen atoms from O2 into phenol, revealing in detail the pathway for photocatalytic benzene hydroxylation. This study demonstrates that the photochemistry approach is an appealing strategy for the synthesis of high‐performance OVs‐rich photocatalysts for solar‐induced chemical conversion.

Fully Fused Indacenodithiophene-Centered Small-Molecule n-Type Semiconductors for High-Performance Organic Electronics.

Developing novel n-type organic semiconductors is an on-going research endeavour, given their pivotal roles in organic electronics and their relative scarcity compared to p-type counterparts. In this study, a new strategy was employed to synthesize n-type organic semiconductors featuring a fully fused conjugated backbone. By attaching two sets of adjacent amino and formyl groups to the indacenodithiophene-based central cores and triggering a tandem reaction sequence of a Knoevenagel condensation-intramolecular cyclization, DFA1 and DFA2 were realized. The solution-processed organic field effect transistors based on DFA1 exhibited unipolar n-type transport character with a decent electron mobility of ca. 0.10 cm2 V-1 s-1 (ca. 0.038 cm2 V-1 s-1 for DFA2 based devices). When employing DFA1 as a third component in organic solar cells, a high power conversion efficiency of 19.2 % can be achieved in ternary devices fabricated with PM6 : L8-BO : DFA1. This work provides a new pathway in the molecular engineering of n-type organic semiconductors, propelling relevant research forward.

Constructing the Electron-Rich Microenvironment of an All-Polymer-Based S-Scheme Homostructure for Accelerating Uranium Capture from Nuclear Wastewater.

Large quantities of uranium-containing radioactive wastewater are typically generated during nuclear fuel cycle processes. Despite significant efforts, efficient capture of migratable hexavalent uranium U(VI) is still a huge challenge due to its acidity, radioactivity, coexisting organics, and high impurity cation abundance in wastewater. Herein, we have fabricated all-polymer-based 0D/2D C4N/C6N7 homostructure hybrids with an S-scheme electronic configuration by coordinating the band engineering of semiconductors to enrich uranium species from the complex wastewater environment. The sample can capture over 97% of U(VI) in the actual concentration of nuclear industrial reprocessing wastewater; also, the U(VI) enrichment ratio still exceeds 95% when the irradiation dose (including α, β, and γ) is up to 100 kGy. Density functional theory and X-ray absorption spectroscopy demonstrate that the aggregation of charge carriers on the surface of the sample regulates the electron-rich microenvironment, thus accelerating the reduction conversion of single electron reaction uranium disproportionation. It is expected that this work can provide more insight into other functional materials, thereby promoting uranium removal advancements in nuclear wastewater.

Ultralow-Energy-Consumption Photosynaptic Transistor Utilizing Conjugated Polymers/Perovskite Quantum Dots Nanocomposites With Ligand Density Optimization.

The photosynaptic transistor stands as a promising contender for overcoming the von Neumann bottleneck in the realm of photo-communication. In this context, photonic synaptic transistors is developed through a straightforward solution process, employing an organic semiconducting polymer with pendant-naphthalene-containing side chains (PDPPNA) in combination with ligand-density-engineered CsPbBr3 perovskite quantum dots (PQDs). This fabrication approach allows the devices to emulate fundamental synaptic behaviors, encompassing excitatory postsynaptic current, paired-pulse facilitation, the transition from short-to-long-term memory, and the concept of "learning experience." Notably, the phototransistor, incorporating the blend of the PDPPNA and CsPbBr3 PQDs washed with ethyl acetate, achieved an exceptional memory ratio of 104. Simultaneously, the same device exhibited an impressive paired-pulse facilitation ratio of 223% at a moderate operating voltage of -4V and an extraordinarily low energy consumption of 0.215 aJ at an ultralow operating voltage of -0.1mV. Consequently, these low-voltage synaptic devices, constructed with a pendant side-chain engineering of organic semiconductors and a ligand density engineering of PQDs through a simple fabrication process, exhibit substantial potential for replicating the visual memory capabilities of the human brain.

Surface Oxygen Defect Engineering of A2B2O7 Pyrochlore Semiconductors Boosts the Electrocatalytic Reduction of CO2-to-HCOOH.

The electrocatalytic conversion of inert CO2 to value-added chemical fuels powered by renewable energy is one of the benchmark approaches to address excessive carbon emissions and achieve carbon-neutral energy restructuring. However, the adsorption/activation of supersymmetric CO2 is facing insurmountable challenges that constrain its industrial-scale applications. Here, this theory-guided study confronts these challenges by leveraging the synergies of bimetallic sites and defect engineering, where pyrochlore-type semiconductor A2B2O7 is employed as research platform and the conversion of CO2-to-HCOOH as the model reaction. Specifically, defect engineering intensified greatly the chemisorption-induced CO2 polarization via the bimetallic coordination, thermodynamically beneficial to the HCOOH production via the *HCO2 intermediate. The optimal V-BSO-430 electrocatalyst with abundant surface oxygen vacancies achieved a superior HCOOH yield of 116.7mmol h-1 cm-2 at -1.2 VRHE, rivalling the incumbent similar reaction systems. Furthermore, the unique catalytic unit featured with a Bi1-Sn-Bi2 triangular structure, which is reconstructed by defect engineering, and altered the pathway of CO2 adsorption and activation to allow the preferential affinity of the suspended O atom in *HCO2 to H. As a result, V-BSO-430 gave an impressive FEHCOOH of 93% at -1.0 VRHE. This study held promises for inspiring the exploration of bimetallic materials from the massive semiconductor database.

Conduction-band engineering of polar nitride semiconductors with wurtzite ScAlN for near-infrared photonic devices

Wurtzite ScxAl1−xN/GaN (x = 0.13–0.18) multi-quantum wells grown by molecular beam epitaxy on c-plane GaN are found to exhibit remarkably strong and narrow near-infrared intersubband absorption in the technologically important 1.8–2.4 μm range. Band structure simulations reveal that, for GaN wells wider than 3 nm, the quantized energies are set by the steep triangular profile of the conduction band caused by intrinsic polarization fields. As a result, the intersubband transition energies provide unique and direct access to essential ScAlN polarization parameters. Measured infrared absorption indicates that the spontaneous polarization difference of the presumed lattice-matched Sc0.18Al0.82N/GaN heterostructure is smaller than the theoretically calculated value. The intersubband transition energies are relatively insensitive to the barrier alloy composition indicating negligible variation of the net polarization field in the probed 0.13–0.18 Sc composition range.

Charged Exciton Generation by Curvature-Induced Band Gap Fluctuations in Structurally Disordered Two-Dimensional Semiconductors.

Curvature is a general factor for various two-dimensional (2D) materials due to their flexibility, which is not yet fully unveiled to control their physical properties. In particular, the effect of structural disorder with random curvature formation on excitons in 2D semiconductors is not fully understood. Here, the correlation between structural disorder and exciton formation in monolayer MoS2 on SiO2 was investigated by using photoluminescence (PL) and Raman spectroscopy. We found that the curvature-induced charge localization along with band gap fluctuations aid the formation of the localized charged excitons (such as trions). In the substrate-supported region, the trion population is enhanced by a localized charge due to the microscopic random bending strain, while the trion is suppressed in the suspended region which exhibits negligible bending strain, anomalously even though the dielectric screening effect is lower than that of the supported region. The redistribution of each exciton by the bending strain leads to a huge variation (∼100-fold) in PL intensity between the supported and suspended regions, which cannot be fully comprehended by external potential disorders such as a random distribution of charged impurities. The peak position of PL in MoS2/SiO2 is inversely proportional to the Raman peak position of E12g, indicating that the bending strain is correlated with PL. The supported regions exhibit an indirect portion that was not shown in the suspended regions or atomically flat substrates. The understanding of the structural disorder effect on excitons provides a fundamental path for optoelectronics and strain engineering of 2D semiconductors.

High-quality semiconductor fibres via mechanical design

Recent breakthroughs in fibre technology have enabled the assembly of functional materials with intimate interfaces into a single fibre with specific geometries1–11, delivering diverse functionalities over a large area, for example, serving as sensors, actuators, energy harvesting and storage, display, and healthcare apparatus12–17. As semiconductors are the critical component that governs device performance, the selection, control and engineering of semiconductors inside fibres are the key pathways to enabling high-performance functional fibres. However, owing to stress development and capillary instability in the high-yield fibre thermal drawing, both cracks and deformations in the semiconductor cores considerably affect the performance of these fibres. Here we report a mechanical design to achieve ultralong, fracture-free and perturbation-free semiconductor fibres, guided by a study on stress development and capillary instability at three stages of the fibre formation: the viscous flow, the core crystallization and the subsequent cooling stage. Then, the exposed semiconductor wires can be integrated into a single flexible fibre with well-defined interfaces with metal electrodes, thereby achieving optoelectronic fibres and large-scale optoelectronic fabrics. This work provides fundamental insights into extreme mechanics and fluid dynamics with geometries that are inaccessible in traditional platforms, essentially addressing the increasing demand for flexible and wearable optoelectronics.

Solution Process-Based Thickness Engineering of InZnO Semiconductors for Oxide Thin-Film Transistors with High Performance and Stability.

To fabricate oxide thin-film transistors (TFTs) with high performance and excellent stability, preparing high-quality semiconductor films in the channel bulk region and minimizing the defect states in the gate dielectric/channel interfaces and back-channel regions is necessary. However, even if an oxide transistor is composed of the same semiconductor film, gate dielectric/channel interface, and back channel, its electrical performance and operational stability are significantly affected by the thickness of the oxide semiconductor. In this study, solution process-based nanometer-scale thickness engineering of InZnO semiconductors was easily performed via repeated solution coating and annealing. The thickness-controlled InZnO films were then applied as channel regions, which were fabricated with almost identical film quality, gate dielectric/channel interface, and back-channel conditions. However, excellent operational stability and electrical performance suitable for oxide TFT backplane was only achieved using an 8 nm thick InZnO film. In contrast, the ultrathin and thicker films exhibited electrical performances that were either very resistive (high positive VTh and low on-current) or excessively conductive (high negative VTh and high off-current). This investigation confirmed that the quality of semiconductor materials, solution process design, and structural parameters, including the dimensions of the channel layer, must be carefully designed to realize high-performance and high-stability oxide TFTs.

Overcoming the limitations of atomic-scale simulations on semiconductor catalysis with changing Fermi level and surface treatment

A new groundbreaking method for efficient optimization of doping concentration and cocatalyst materials for Fermi level engineering of wide band gap semiconductors.

Advances in the structural engineering of layered bismuth-based semiconductors for visible light-driven photocatalytic water splitting.

Hydrogen production via the photocatalytic water splitting reaction on semiconductors presents a promising avenue to directly achieve solar energy conversion and storage. Bismuth-based semiconductors with layered structures, a hierarchical arrangement of components stacked in the form of two-dimensional extended layers where the atoms within each layer are typically strongly bonded, while the interactions between the layers are relatively weak, have emerged as an important series of photocatalyst candidates. In this review, we focus on the new emerging layered bismuth-based semiconductors with structures in Sillén, Aurivillius, Sillén-Aurivillius and bismuth chromate systems primarily employed in the photocatalytic water splitting reaction. From a crystal structure-oriented view, we delve into discussions on how the component and unit of a crystal structure influence the intrinsic properties, including light absorption and photogenerated charge transfer and separation, of materials as well as the corresponding photocatalytic performance of the water splitting reaction. The strategies for modulating the ferroelectricity and surface modification of these layered bismuth-based semiconductors are also involved. We also discuss the limitations of these materials accompanied by a forward-looking perspective, and we hope to provide some insights from the view of rational material design and engineering for the fabrication of high-efficiency photocatalytic water splitting systems.

Backbone-shape engineering of fused-ring electron-deficient molecular semiconductors for unipolar n-type organic transistors: synthesis, conformation changes, and structure–property correlations

Three n-type fused-ring small molecules with different shapes are synthesized. Changing the backbone shape is found to affect the energy levels, molecular conformation and packing ordering, leading to different charge transport properties.

Defect Engineering of 2D Semiconductors for Dual Control of Emission and Carrier Polarity.

2D transition metal dichalcogenides (TMDCs) are considered as promising materials in post-Moore technology. However, the low photoluminescence quantum yields (PLQY) and single carrier polarity due to the inevitable defects during material preparation are great obstacles to their practical applications. Here, an extraordinary defect engineering strategy is reported based on first-principles calculations and realize it experimentally on WS2 monolayers by doping with IIIA atoms. The doped samples with large sizes possess both giant PLQY enhancement and effective carrier polarity modulation. Surprisingly, the high PL emission maintained even after one year under ambient environment. Moreover, the constructed p-n homojunctions shows high rectification ratio (≈2200), ultrafast response times and excellent stability. Meanwhile, the doping strategy is universally applicable to other TMDCs and dopants. This smart defect engineering strategy not only provides a general scheme to eliminate the negative influence of defects, but also utilize them to achieve desired optoelectronic properties for multifunctional applications.

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).

The design and characterisation of a Z-scheme Bi2O2S/ZnO heterojunction photoanode for the photoelectrochemical removal of ciprofloxacin in synthetic and real wastewater

Towards the engineering of semiconductors for improved visible light photoelectrochemical degradation of organic pollutants in wastewater, we present the preparation of a Z-scheme heterojunction of Bi2O2S and ZnO nanoparticles for the removal of ciprofloxacin from wastewater. The Bi2O2S/ZnO nanocomposite heterojunction was synthesised via an in-situ hydrothermal method and deposited on FTO substrate to form the photoanode. The semiconductors and the photoanodes were characterised with electron microscopy, XRD, photo-electrochemistry, photoluminescence, XPS and UV/Vis diffusive reflectance techniques. The degradation of ciprofloxacin was enhanced by the heterojunction in comparison with the Bi2O2S and ZnO photoanodes. We attribute the enhanced performance to the presence of an internal electric field (IEF), the low rate of recombination of photogenerated electrons and holes, lower charge transfer resistance, and high photocurrent density of the heterojunction based on data from photoluminescence, electrochemical impedance spectroscopy, XPS, and photocurrent response. The extent of mineralisation of ciprofloxacin was calculated as 86 % from total organic carbon (TOC) measurement. LC-MS analysis provided the degradation pathway and premise for the reaction scheme, while quantitative structure–activity relationship (QSAR) model was used to predict the toxicity of the intermediate and by-product. The Bi2O2S/ZnO photoanode was stable after seven treatment cycles. The photoelectrochemical reactor was used in the treatment of ciprofloxacin in real wastewater with 87 % TOC removal. Thus, the paper reveals the performance of a unique Z scheme band gap engineering of semiconductors for application in the removal of pharmaceuticals in wastewater.

Dimensionality Engineering of Lead Organic Chalcogenide Semiconductors.

Two-dimensional (2D) metal organic chalcogenides (MOCs) such as silver phenylselenolate (AgSePh) have emerged as a new class of 2D materials due to their unique optical properties. However, these materials typically exhibit large band gaps, and their elemental and structural versatility remain significantly limited. In this work, we synthesize a new family of 2D lead organic chalcogenide (LOC) materials with excellent structural and dimensionality tunability by designing the bonding ability of the organic molecules and the stereochemical activity of the Pb lone pair. The introduction of electron-donating substituents on the benzenethiol ligands results in a series of LOCs that transition from 1D to 2D, featuring reduced band gaps (down to 1.7 eV), broadband emission, and strong electron-phonon coupling. We demonstrated a prototypical single crystal photodetector with 2D LOC that showed the dimensionality engineering on the transport property of LOC semiconductors. This study paves the way for further development of the synthesis and optical properties of novel organic-inorganic hybrid 2D materials.

Comparative coherence between layered and traditional semiconductors: unique opportunities for heterogeneous integration

Abstract As Moore’s law deteriorates, the research and development of new materials system are crucial for transitioning into the post Moore era. Traditional semiconductor materials, such as silicon, have served as the cornerstone of modern technologies for over half a century. This has been due to extensive research and engineering on new techniques to continuously enrich silicon-based materials system and, subsequently, to develop better performed silicon-based devices. Meanwhile, in the emerging post Moore era, layered semiconductor materials, such as transition metal dichalcogenides (TMDs), have garnered considerable research interest due to their unique electronic and optoelectronic properties, which hold great promise for powering the new era of next generation electronics. As a result, techniques for engineering the properties of layered semiconductors have expanded the possibilities of layered semiconductor-based devices. However, there remain significant limitations in the synthesis and engineering of layered semiconductors, impeding the utilization of layered semiconductor-based devices for mass applications. As a practical alternative, heterogeneous integration between layered and traditional semiconductors provides valuable opportunities to combine the distinctive properties of layered semiconductors with well-developed traditional semiconductors materials system. Here, we provide an overview of the comparative coherence between layered and traditional semiconductors, starting with TMDs as the representation of layered semiconductors. We highlight the meaningful opportunities presented by the heterogeneous integration of layered semiconductors with traditional semiconductors, representing an optimal strategy poised to propel the emerging semiconductor research community and chip industry towards unprecedented advancements in the coming decades.