Low Defect Concentration Research Articles

Investigating the atomic structures and electronic properties of WS2 thin films with sulfur vacancies via a neural network potential-aided first-principles study

Transition metal dichalcogenides are promising materials for high-performance electronics, whereas the impact of defects on their electronic properties remains elusive. Here, we employ neural network potentials (NNPs) constructed from density functional theory (DFT) data to investigate defect-laden WS2 thin films. Molecular dynamics simulations reveal that at low defect concentrations (S/W ratio of 1.9), single sulfur vacancies are predominant. Conversely, at high defect concentrations (S/W ratio of 1.7), complex defects with short lifetimes appear. Additionally, DFT results indicate that the band gap persists at S/W = 1.9 but disappears at 1.7, aligning with observed device degradation at high defect concentrations.

Optimizing cooling strategies in the Czochralski process for large-diameter silicon ingots

As the semiconductor industry shifts towards larger wafer sizes, such as 300 mm and 450 mm, controlling defects is crucial to ensure device performance and yield. Conversely, a high cooling rate is essential for achieving higher production rates. Therefore, finding the optimal cooling strategy is critical to maintaining high production rates while ensuring high-quality wafer production. This paper employs a simulation model to investigate the impact of various cooling strategies on point defect formation during the CZ process for 450 mm diameter silicon ingots. Using the 3D energy equation coupled with the Navier-Stokes equation and moving mesh theory, the transient CZ process is simulated, incorporating defect evaluation equations. Beside original CZ puller configuration, two cooling strategies are examined: one with a small gap and long cooling jacket (Case II) and another with a large gap and short cooling jacket (Case III), compared against a baseline setup (Case I). The simulations reveal that Case II, while enhancing the crystallization rate, increases non-uniformity. Conversely, Case III produces a flatter solid-liquid interface and lower defect concentrations, achieving a maximum Cv-Ci of 0.4 × 1014 cm−3, compared to 1.1 × 1014 cm−3 and -2.5 × 1014 cm−3 in Case I and II. These findings suggest that adjusting cooling strategies can significantly impact the quality and uniformity of large- diameter silicon ingots.

Optimizing electron transport layers for high-efficiency perovskite solar cells using impedance spectroscopy

The best interface for a perovskite solar cell is designed to facilitate effective charge transport to achieve a high-power conversion efficiency. Tin dioxide (SnO2) is widely recognized as an electron transport material for perovskite solar cells, offering advantages such as low hysteresis, low defect concentration, and low fabrication temperature. However, the low conduction band edge of SnO2 restricts the built-in potential of the solar cell device. In this study, we designed a double layer of electron transport by applying zinc oxide (ZnO) on SnO2 to improve the electron transport properties in perovskite solar cells. The bilayer of electron transport enhances the interfaces between the perovskite and the electron transport layer, leading to an improvement in the efficiency and stability of solar cell devices up to 11.71 % compared to a single SnO2 layer device with a PCE of 9.06 %. The introduction of ZnO reduces charge recombination, resulting in a lower recombination resistance (Rrec). Also, charge transfer resistance (Rct) of ZnO/SnO2 increased to 16.6KΩ compared to a single SnO2 layer device with a Rct of 5.29KΩ. Our findings provide valuable insights into the design of electron transport layers for perovskite solar cells and highlight the importance of electrochemical impedance spectroscopy in understanding the dynamic processes that govern their performance.

Minimum Energy Atomic Deposition: A novel, efficient atomistic simulation method for thin film growth

Thin-film growth is an area of research concerned with complex phenomena happening at atomic scales. Therefore, molecular simulation has been an important tool to confront experimental results to theoretical assumptions. However, the traditional thin film growth simulation methods, i.e., Molecular Dynamics (MD) and kinetic Monte-Carlo (kMC) and combinations thereof, suffer from limitations inherent to their design, i.e., limitations in system size and simulation time for MD and predetermined reaction rates and reaction sites for kMC. Consequently, it is practically impossible to simulate the evolution of polycrystalline growth resulting in ∼100nm thick films with realistic stress fields and defect structures, such as grain boundaries, stacking faults, etc. In this work, we propose a versatile and efficient atomistic simulation method (Minimum Energy Atomic Deposition) which works by direct insertion of atoms at points of minimal potential energy through efficient scanning of candidate positions and rapid relaxation of the system. This method allows simulating ≥100nm film thickness while mimicking experimental growth rates and high crystallinity and low-defect concentration and enables in-depth studies of atomic growth mechanisms, the evolution of crystal defects, and residual stress build-up. We demonstrate the efficiency and versatility of the method through the deposition of Al on Si, Al on Al, and Si on Si. The simulation results are systematically compared with experimental observations of thin-film deposition, yielding consistent observations. The method has been implemented in open-source LAMMPS software, making it easily accessible to the research community.

Porous Structure Enhances the Longitudinal Piezoelectric Coefficient and Electromechanical Coupling Coefficient of Lead-Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3.

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d33) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, this paper demonstrates an unusual 22-41% enhancement in the d33 compared to its dense counterpart. This unique combination of high d33 and a low permittivity leads to a significantly improved voltage coefficient (g33), energy harvesting figure of merit (FoM33) and electromechanical coupling coefficient ( ). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators.

Optimizing methane plasma pyrolysis for instant hydrogen and high-quality carbon production

The European Green Deal has set a target for Europe to achieve net-zero greenhouse gas emissions by 2050, necessitating a transition to more sustainable energy sources. Hydrogen gas (H2) has emerged as a promising solution, with methane pyrolysis presenting a viable method for its production. This study explores the optimization of methane plasma pyrolysis for hydrogen and high-quality carbon production. Employing a statistical approach by a design of experiment software, critical process parameters are systematically analyzed to predict their impact within a defined range. Additionally, the paper conducts comprehensive characterization of the solid carbon produced during pyrolysis using imaging, spectroscopic and elemental analysis, and gas sorption analysis methods. The experimental investigation was conducted using a thermal plasma reactor with several settings of influential parameters including methane gas (CH4) content in the plasma gas, electric current, and arc length. The DC-transferred plasma arc is formed using a variable gas mixture of argon gas (Ar) and CH4, with a constant flow rate of 5 Nl/min. Thirteen tests were designed, evaluating responses such as power input, process stability, and H2 yield. The H2 yield indicates the hydrogen produced from CH4, with 100% representing total conversion. While the process exhibited inconstancy, attributed to reactor design constraints, a high H2 yield of 67%–100% was achieved. The results indicate that a higher CH4 content in the plasma gas and extended arc lengths disturb the plasma arc, hence reducing the H2 yield. Increased power input, achieved through higher amperage levels, and a wider reaction zone eased by extending the arc length both led to an improved H2 yield. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) revealed microstructural differences, with carbon samples from the filter exhibiting finer textures and carbon samples from the reactor larger sizes and dendritic particles. Raman spectroscopy confirmed crystalline graphitic-like structures with low defect concentrations, a finding supported by X-ray diffraction (XRD) analysis. Inductively coupled plasma mass spectroscopy (ICP-MS) analysis confirmed high-purity carbon with slight impurities from initial filter contamination. Brunauer-Emmett-Teller (BET) specific surface area calculations based on gas sorption analysis showed significant variations, with filter-collected samples exhibiting 40–170 m2/g and reactor-collected ones showing 7–30 m2/g.

The Elaborate Design of Multi‐Polarization Effect by Non‐Edge Defect Strategy for Ultra‐Broad Microwave Absorption

AbstractAnion defect engineering is proven to be an efficient approach to reconstruct the electronic configuration of carbon‐based magnetoelectric materials for targeted modulation of electromagnetic (EM) performance. However, traditional mono‐anionic doping suffers from low defect concentration and lacks diverse polarization mechanisms. In this work, multi‐anions (N/S/F) stepwise‐doped carbon/Fe3C magnetoelectric composites are elaborately constructed, wherein the predesigned N defects serve as activated sites for anomalously adopting S anions (Step I) and subsequent F anions (Step II) in non‐marginal areas of the carbon layer. It is found that S prefers to replace pyrrolic N defects while F tends to form dangling bonds with the C site adjacent to the pyridinic N. Intriguingly, besides the inherent polarized resonance of N defect at ≈15 GHz, customized S and F defects induce new polarization resonances at ≈10 GHz and ≈15+ GHz, respectively. Under a typical multi‐polarization effect with the synergetic magnetic response, the carbon/Fe3C composites with N/S/F defects harvest the broadest bandwidth of 8.28 GHz (9.72–18 GHz) at 2.55 mm, covering a wide frequency range almost from X to Ku bands. This work demonstrates the positive impact of localized multi‐defects customization and multi‐polarization effect on expanding microwave absorption bandwidth, providing valuable insights for the advanced design of ultra‐broadband absorbers.

CVD growth of large-area, continuous, and defect-free MoS2 multilayer films from solution-cast seed nanoflakes

Defects in transition metal dichalcogenides are among the primary source of their chemical reactivity, including their response to water. The CVD growth of defect-free continuous molybdenum disulfide (MoS2) films has been particularly challenging. In this work, we demonstrate the growth of large-area continuous films of MoS2 using solution-cast MoS2 seed nanoflakes, both with and without the assistance of alkali halide. The MoS2 seed nanoflakes serve as nucleation sites for the in-plane growth of few-layer MoS2, which is accompanied by localized vertical growth of MoS2 particles. For films grown with the combination of seed and NaCl, very low oxygen content was observed together with the stoichiometric ratio of Mo: S being close to the ideal value of 1: 2. These films show humidity-insensitive electrical response over a wide interval (5%–95% RH). This is attributed to very low concentrations of edge and basal-plane defects, leading to low water dissociation and restricted proton transport.

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Dielectric properties of hafnium oxide film prepared by HiPIMS at different O2/Ar ratios and their influences on TFT performance

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to higher crystallinity, higher density, and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased, thereby leading to lower crystallinity, lower density, and higher oxygen vacancy defect concentration of the film, therefore deteriorating the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric field (4.7 MV/cm), which should be attributed to the high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance, featuring a remarkably low subthreshold swing of 0.13 V/decade. It also exhibited fair stability against bending and gate bias stress.

High-κ Wide-Gap Layered Dielectric for Two-Dimensional van der Waals Heterostructures.

van der Waals heterostructures of two-dimensional materials have unveiled frontiers in condensed matter physics, unlocking unexplored possibilities in electronic and photonic device applications. However, the investigation of wide-gap, high-κ layered dielectrics for devices based on van der Waals structures has been relatively limited. In this work, we demonstrate an easily reproducible synthesis method for the rare-earth oxyhalide LaOBr, and we exfoliate it as a 2D layered material with a measured static dielectric constant of 9 and a wide bandgap of 5.3 eV. Furthermore, our research demonstrates that LaOBr can be used as a high-κ dielectric in van der Waals field-effect transistors with high performance and low interface defect concentrations. Additionally, it proves to be an attractive choice for electrical gating in excitonic devices based on 2D materials. Our work demonstrates the versatile realization and functionality of 2D systems with wide-gap and high-κ van der Waals dielectric environments.

Chemical Aspects of Halide Perovskite Nanocrystals.

Halide perovskite nanocrystals (HPNCs) are currently among the most intensely investigated group of materials. Structurally related to the bulk halide perovskites (HPs), HPNCs are nanostructures with distinct chemical, optical, and electronic properties and significant practical potential. One of the keys to the effective exploitation of the HPNCs in advanced technologies is the development of controllable, reproducible, and scalable methods for preparation of materials with desired compositions, phases, and shapes and low defect content. Another important condition is aquantitative understanding of factors affecting the chemical stability and the optical and electronic properties of HPNCs. Here we review important recent developments in these areas. Following a brief historical prospective, we provide an overview of known chemical methods for preparation of HPNCs and approaches used to control their composition, phase, size, and shape. We then review studies of the relationship between the chemical composition and optical properties of HPNCs, degradation mechanisms, and effects of charge injection. Finally, we provide a short summary and an outlook. The aim of this review is not to provide a comprehensive summary of all relevant literature but rather aselection of highlights, which, in the subjective view of the authors, provide the most significant recent observations and relevant analyses.

Origin of linear magnetoresistance in Bi2Te3 topological insulator: Role of surface state and defects

Connection between topological surface states (TSS) and large linear magnetoresistance (LMR) is established in tetradymite Bi2Te3 through tuning of native defects. Thorough analysis of temperature dependent synchrotron X-ray diffraction data quantifies 0-D, 1-D and 2-D defect concentrations. Plausible variation of antisite defects is explained via carrier concentration data. Resistivity data divulge contribution of mixed bulk and surface states in the synthesized samples. High Fermi velocity (∼106 ms−1) and low Fermi energy (∼14 meV) of carriers are obtained. Lower defect concentration sample emerges with high magnetoresistance (MR) and higher mobility. Weak antilocalization (WAL) effect, signature of TSS, is revealed from MR. Large (80%), non-saturating LMR along with ultrahigh mobility (∼1 m2V−1s−1) in Bi2Te3 supports the presence of TSS. Magnetoconductance data are fitted with Hikami-Larkin-Nagaoka equation, obtaining further insight on WAL effect. In addition, extracted parameters like disorder correlation length and coherence length explicate the role of defect density on LMR.

Suppressing substrate oxidation during plasma-enhanced atomic layer deposition on semiconductor surfaces

Plasma-enhanced atomic layer deposition (PE-ALD) is widely employed in microelectronics, energy, and sensing applications. Typically, PE-ALD processes for metal oxides utilize remote inductively coupled plasmas operated at powers of >200 W, ensuring a sufficient flux of oxygen radicals to the growth surface. However, this approach often leads to significant oxidation of chemically sensitive substrates, including most technological semiconductors. Here, we demonstrate that plasma powers as low as 5 W can effectively suppress substrate oxidation while maintaining the structural, optical, and electronic quality of the films. Specifically, we investigate the growth of titanium oxide (TiOx) using two commonly used metalorganic precursors, titanium isopropoxide and tetrakis(dimethylamino)titanium. Films deposited with 5 and 300 W oxygen plasma power are nearly indiscernible from one another, exhibiting significantly lower defect concentrations than those obtained from thermal ALD with H2O. The low plasma power process preserves desired physical characteristics of PE-ALD films, including large optical constants (n > 2.45 at 589 nm), negligible defect-induced sub-bandgap optical absorption (α < 102 cm−1), and high electrical resistivity (>105 Ω cm). Similar behavior, including suppressed interface oxidation and low defect content, is observed on both Si and InP substrates. As an example application of this approach, the assessment of InP/TiOx photocathodes and Si/TiOx photoanodes reveals a significant improvement in the photocurrent onset potential in both cases, enabled by suppressed substrate oxidation during low power PE-ALD. Overall, low power PE-ALD represents a generally applicable strategy for producing high quality metal oxide thin films while minimizing detrimental substrate reactions.

Dimethylamine oxalate manipulating CsPbI3 perovskite film crystallization process for high efficiency carbon electrode based perovskite solar cells

Crystallization process determines the quality of perovskite films and the performances of resultant perovskite solar cells (PSCs). Dimethylamine oxalate has been proven as a multifunctional modulator, and is explored as an efficient additive in manipulating the crystallization process of CsPbI3 perovskite films. On one hand, oxalate serves as the precipitator that facilitates the nucleation process of intermediate. The larger size of intermediate is conductive to the larger size and smaller grain boundaries of resultant perovskite. On the other hand, in subsequent annealing process, the phase conversion and growth process of transient perovskite can be decelerated due to the strong interactions of oxalate with both dimethylamine cation (DMA+) and Pb2+. Due to the optimized crystallization kinetics, the morphology and quality of CsPbI3 perovskite films are comprehensively improved with lower defect concentrations, and charge recombination loss is effectively suppressed. Benefiting from the optimized crystal quality of perovskite films, the carbon electrode-based CsPbI3 PSCs exhibit a champion efficiency of 18.48%. This represents one of the highest levels among all hole transport layer-free inorganic perovskite solar cells.

Heterogeneous Integration of Graphene and HfO2 Memristors

AbstractThe past decade has seen a growing trend toward utilizing (quasi) van der Waals growth for the heterogeneous integration of various materials for advanced electronics. In this work, pulsed‐laser deposition is used to grow HfO2 thin films on graphene/SiO2/Si. As graphene is easily damaged under standard oxide‐film deposition conditions, the process needs to be adjusted to minimize the oxidation and the collision‐induced damage. A systematic study is conducted in order to identify the crucial deposition parameters for diminishing the defect concentration in the graphene interlayer. For evaluating the quality of graphene, it is mainly relied on data obtained from Raman spectroscopy, using approaches beyond the Tuinstra‐Koenig relation. The results show that the defects are mainly a consequence of the high kinetic energy of the plasma‐plume particles. Using a relatively high Ar process pressure, a sufficiently low defect concentration is ensured, without compromising the quality of the HfO2 thin film. This enabled us to successfully prepare memristive devices with a filamentary type of switching, utilizing the graphene layer as a bottom electrode. The findings of this study can be easily transferred to other systems for the development of oxide electronic devices.

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Engineering lattice oxygen defects and polaronic transport in vanadium pentoxide via isovalent phosphorus doping

Oxygen vacancies are equilibrium defects in the vanadium pentoxide system that give rise to polaronic hopping transport via V4+ charge compensating defect. In this paper, we report the tunability of polaron formation, the hopping process, and their magnetic signature by substitution of isovalent (5+) phosphorus ions in the V5+ site. The powder x-ray diffraction data show a monotonous shift in lattice parameters with progressive P-doping, confirming the presence of a substitutional dopant. The polaron hopping energy reduced from 0.307 to 0.290 eV depicting a lower defect concentration in P-doping in V2O5. At low temperatures, it is found to obey the Efros–Shklovskii variable range hopping mechanism. The estimated hopping range increased to 1.6 ± 0.1 nm in doped V2O5 in contrast to ∼1.3 nm in the undoped one. The electron spin resonance measurements show a diminishing broad ferromagnetic signal and rising paramagnetic signal (g = 1.97) with progressive P-doping depicting predominant isolated electronic spins in the doped sample. The same is corroborated in room temperature M–H with a distinct hysteresis that diminishes with P-doping and a rise of a paramagnetic slope. Moreover, the reduced oxygen defects and lower V4+ relative occupancy together with fermi level fall toward intrinsic position are substantiated by photoelectron emission studies.

Tuning the growth of intermetallic compounds at Sn-0.7Cu solder/Cu substrate interface by adding small amounts of indium

The void defect in intermetallic compounds (IMCs) layer at the joints caused by inhomogeneous atomic diffusion is one of the most important factors limiting the further development of Sn-based solders. In this work, the thermodynamic stability of IMCs (high-temperature η-Cu6Sn5 and o-Cu3Sn phases) was improved by adding small amounts of indium (In), and the IMCs layers with moderate thickness, low defect concentrations and stable interface bonding were successfully obtained. The formation order of compounds and the interfacial orientation relationships in IMCs layers, the atomic diffusion mechanism, and the growth tuning mechanism of In on η-Cu6Sn5 and Cu3Sn, after In adding, were discussed comprehensively by combining calculations and experiments. It is the first time that the classic heterogeneous nucleation theory and CALPHAD data were used to obtain the critical nucleus radius of η-Cu6Sn5 and Cu3Sn, and to explain in detail the main factors affecting the formation order and location of IMCs at joints during the welding process. A novel and systematic growth model about IMCs layers in the case of doping with alloying elements was proposed. The growth tuning mechanism of In doping on η-Cu6Sn5 and Cu3Sn was further clarified based on the proposed model using first-principles calculations. The growth model used in this study can provide insights into the development and design of multielement Sn-based solders.

Enhancing Performance of Ultraviolet C Photodetectors Through Single-Domain Epitaxy of Monoclinic β-Ga2 O3 Films and Tailored Anti-Reflection Coating.

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga2 O3 films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga2 O3 films on a hexagonal sapphire substrate. Unlike 3D β-Ga2 O3 films with twin domains, 2D β-Ga2 O3 films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga2 O3 films and the application of ARC for the development of high-performance UVC PDs.