Band Structure Research Articles

Enhanced On-State Current and Stability in Heterojunction ITO/ZnO Transistors: A Mechanistic Analysis

The growing demand for high-performance oxide transistors in advanced integrated circuits (ICs) underscores the need for innovative device structures, with heterojunctions emerging as a promising approach. This study presents high-performance ITO/ZnO transistors, which outperform individual ITO or ZnO transistors by achieving an on-state current of 19.2 μA/μm at a drain voltage of 1 V and exhibiting a minimal threshold voltage shift of −0.16 V under negative bias illumination stress. Band structure analysis reveals that the differences in the conduction band minimum and Fermi level between the ZnO and ITO films lead to the formation of a potential well at the ITO/ZnO interface. Furthermore, the increase in the on-state current is attributed to electron confinement at the ITO/ZnO interface, while the enhanced NBIS stability is ascribed to both the band structure and ZnO passivation. These findings make significant contributions to both optimizing the performance and analyzing the mechanisms of oxide devices, highlighting the potential of high-performance ITO/ZnO transistors in 3D integrated circuits, advanced memory devices, and back-end-of-line (BEOL) processes.

Unlocking the potential of FeNbGe Half Heusler: stability, electronic, magnetic and thermodynamic properties

Abstract In this paper, we investigate the electronic, magnetic, mechanical, dynamical, and thermodynamical properties of novel FeNbGe half Heusler alloy by first principle calculations. The alloy’s thermodynamic and dynamic stability were verified, and it was found feasible to synthesize experimentally. The calculated elastic constants prove the mechanical stability of the material. The malleable and ductile nature of the material was confirmed through Pugh’s and Poisson’s ratios. The electronic properties were calculated using the GGA and TB-mBJ exchange-correlation potentials. The band structure in the spin-down channel reflects metallic behaviour. In contrast, the spin-up channel shows non-metallic behaviour, which infers the half-metallic property of our half-Heusler alloy, which is a desirable property for spintronic materials. The alloy displayed an indirect band gap of 1.06 eV from GGA and 1.15 eV from TB-mBJ functionals. The Heusler alloy under study with 17 valence electrons, was found to be a Ferromagnetic alloy with a total magnetic moment of −1μ B . The half-metallicity retaining property was studied by imposing expansive volumetric strain. The small band gap, half-metallic property, and the ferromagnetic nature of our material suggest that it can be a suitable material for spintronics applications.

Complex thermoelectric transport in Bi-Sb alloys

Bi1−xSbx alloys are classic thermoelectric materials for near-cryogenic applications. Despite more than half a century of study, unraveling the underlying transport physics within this space has been nontrivial due to the complex electronic structure, disorder, and small bandgap within these alloys. Furthermore, as Peltier coolers, Bi1−xSbx alloys operate in a bipolar regime; as such, understanding the impact of minority carriers is critical for further improvements in device performance. This study unites first principles calculations with low-temperature experimental measurements to create a generalized model for transport within semiconducting Bi-Sb alloys. Our exploration reveals the interplay between the complex, degenerate valence band structure with the extremely light conduction bands. By building a hybrid computational/experimental model, an understanding of both the electron and hole relaxation times emerges both as a function of temperature and energy. Special quasi-random supercell calculations reveal that, despite significant atomic disorder, the electronic band structures within the alloy remains largely unaffected and electron–phonon scattering dominates. For charge carriers near the band edges, the relaxation times are thus extremely long, consistent with cyclotronic behavior appearing at low magnetic fields (≪ 1 T). Modeling thermoelectric performance suggests that the valence band edge deformation potential is significantly weaker and highlights the potential for p-type compositions to meet or exceed the current n-type alloys.

Elementally Doped Carbonized Polymer Dots: Control of Optical Properties and Their Versatile Applications

AbstractCarbonized polymer dots (CPDs) are a class of luminescent nanomaterials formed through cross‐linking and polymerization. Owing to their excellent biocompatibility, ease of synthesis, good aqueous dispersion, high chemical stability, unique cross‐linking structure, and modifiable surface properties, CPDs have attracted significant attention. However, pure CPDs exhibit certain limitations in terms of optical performance, particularly in terms of fluorescence intensity, phosphorescence intensity, and emission wavelength tunability, which may not meet the requirements of specific applications. To address these limitations, doping CPDs with various elements, such as nitrogen (N), sulfur (S), and phosphorus (P) to modify their band structure and surface functionalization can significantly enhance their optical properties and photochemical stability, thereby expanding their application potential. This paper reviews the main synthesis methods for elementally doped CPDs, examines the effects of different types of elemental doping on their photochemical properties, and explores promising applications in optoelectronic devices, sensors, and catalysis. Finally, recent advancements in elementally doped CPDs are summarized, along with future development directions and challenges.

Electronic Band Structure of Gallium Sulfide (GaS) with Thickness Reduction Unveiling Parabolic and Pudding Mold Band Dispersion

Electronic Band Structure of Gallium Sulfide (GaS) with Thickness Reduction Unveiling Parabolic and Pudding Mold Band Dispersion

Anisotropic Valence Band Structure of Anatase TiO2(101) Studied by Polarization-Dependent Angle-Resolved Photoelectron Spectroscopy

Anisotropic Valence Band Structure of Anatase TiO₂(101) Studied by Polarization-Dependent Angle-Resolved Photoelectron Spectroscopy

Performance analysis of metallo-dielectric optical filters designed using dispersion relations

We present an experimental validation of an analytical approach to predict the spectral response of multilayer metallo-dielectric structures, with applications in the efficient design of bandpass optical filters. Instead of relying on trial-and-error methods, our approach—referred to as the dispersion relation method—is based on intrinsic physical relations, potentially resulting in a significant reduction in time and resources during the design and optimization process. In our previous work, we illustrated that characteristics of the band structure revealed by the dispersion relation can serve as reasonable estimates for the center wavelengths and bandwidths for finite multilayer structures, as obtained from numerical simulations. In this work, we verify those conclusions with experimental results from metallo-dielectric optical filters prepared via magnetron sputtering. Structures using different metals including Ag, Au, and Al are investigated. We show good agreement between spectral response predictions derived from dispersion relations, numerical simulations using the transfer matrix method, and experimental transmittance spectra of the fabricated structures. Considering this experimental validation, the analytical approach based on dispersion relations can offer an accurate and efficient method for designing metallo-dielectric filter structures. Our approach facilitates the selection of geometric parameters for fabrication and provides valuable insight into the optical characteristics of such structures.

Interlayer Transition Induced Infrared Response in WSe2/WS2 Van Der Waals Heterostructure Photodetectors with Polarization and Self‐Powered Effects

AbstractVan der Waals (vdWs) heterojunction photodetectors based on 2D transition metal dichalcogenides are widely utilized in optoelectronic detection, where the band structure of the heterojunction plays a crucial role in determining the performance of the photodetector. In this study, a WSe2/WS2 vdWs heterostructure photodetector with a type‐II band alignment is fabricated. Benefiting from the efficient separation of photogenerated carriers under the type‐II band alignment, the device exhibits remarkable self‐powered characteristics, achieving a responsivity of 0.32 A/W and a quantum efficiency of 76% at zero bias under 532 nm laser illumination, with a specific detectivity of 6.15 × 1013 Jones. Notably, due to the interlayer transitions of photogenerated carriers, the operating wavelength range of the detector is extended to the telecommunication band (i.e., 1550 nm). Furthermore, the device exhibits a significant ability to detect polarized light, achieving a photocurrent anisotropy ratio of 16 under a 532 nm laser line. This work provides a straightforward approach to realizing a photodetector that integrates self‐powered, broadband, and polarization‐sensitive detection functionalities.

Unveiling the Roles of Lattice Strain by Ni Exsolution on Photothermal Reduction of CO2 Activity in BaTiO3 Catalyst.

The lattice strain influences crystal orientation, facets exposed to external light, and atom rearrangement strongly to affect catalytic activity. However, how to rationally design a metal-oxide heterojunction catalyst with featuring lattice strain is a great challenge. Herein, a facile method is adopted to induce lattice strain upon in situ exsolution of Ni nanoparticles from Ba0.9Ti0.9Ni0.1O3-δ (BTNO) perovskite oxide, hereby enhancing the photothermal reduction of CO2. Lattice strain and Ni-exsolution dual regulation ensure that the Ni-anchored BTNO catalyst displays superb photothermal reduction activity of CO2. It shows a CO yield of 40.50 mmol gcat -1 h-1 and a CH4 yield of 19.62 mmol gcat -1 h-1, which are 14 and 73 times higher than those of BaTiO3. In addition, in situ DRIFTS and density functional theory (DFT) calculations reveal the CO2 reduction pathways and strain modulates the interfacial band structure and enhances the transfer of photogenerated charge. Consequently, this study provides a new approach for achieving highly efficient photothermal catalytic reduction of CO2 through strain engineering.

Electron emission efficiency of graphene/h-BN/2D-semiconductor heterostructure: thermotical analysis and experimental verification

Abstract Metal-insulator-semiconductor (MIS) heterostructures have important applications in vacuum microelectronic devices. Among these, graphene-insulator-semiconductor (GIS) heterostructure field electron emitters are among the most widely utilized. Improving the electron emission performance is a major challenge for GIS heterostructure field emitters. A comprehensive theoretical model is needed to predict the electron emission process from such a structure. In this work, a theoretical calculation was carried out on the electron emission current from an GIS heterostructure structure based on a tunneling model that considers the density of states of the semiconductor, scattering of the insulation layer, and hot-hole-induced Auger emission process. Using graphene/h-BN/MoS2 as an example, we obtain the band structure of the MoS2 using first principle calculation, simulate the scattering in h-BN with the Monte Carlo method, and calculate the emission current density using the modified Fowler-Nordheim equation. The results indicate that h-BN thickness and Auger coefficient are key factor affecting emission current density and emission efficiency. To validate our model, a few-layer graphene/h-BN/MoS2 heterostructure device was prepared and the field emission results validate the calculation results. The theoretical model can be expanded to other GIS heterostructures and is useful for designing a high-performance electron source using a GIS tunneling junction.

Phase‐Field Simulation of Carbon Diffusion during Banded Structure Formation in Low‐Carbon Steel

During the cooling process after rolling, low‐carbon steel frequently develops banded structures, primarily due to the segregation of alloying elements and the uneven diffusion of carbon under a slow cooling rate during phase transformation. The current work integrates experiment and simulation to discuss the influence of various cooling rates on ferrite and pearlite bands in Cr–Mn–Ti low‐carbon steel. Meanwhile, a multicomponent multiphase‐field model is established to quantitatively analyze carbon diffusion behavior during the evolution of austenite–ferrite. The results reveal that low cooling rates and the segregation of Mn, Si, and Cr elements can promote the formation of banded structure. Furthermore, in the solute‐poor regions, slow cooling rates allow sufficient time for carbon diffusion during austenite–ferrite transformation, which leads to the extension in both carbon diffusion distance and interface migration distance, thereby generating severe ferrite bands. Additionally, in the solute‐rich regions, as the cooling rate decreases, C concentrations at Ar3 temperature and Ar1 temperature increase, inhibiting the nucleation and growth of ferrite, thereby resulting in strong pearlite bands. This study further elucidates the formation mechanisms of ferrite and pearlite bands, enhancing the understanding of carbon diffusion behavior during banded structure formation.

First-principles investigation of structural, electronic, and optical properties of RVO4 (R = Er, Eu, Tb, Yb) orthovanadates under pressure

Abstract First-principles calculations were performed to systematically study RVO4 orthovanadates with tetragonal zircon- and scheelite-type structures. The study focused on structural parameters, pressure-induced structural phase transformation, electronic band structure, and optical properties under ambient conditions and hydrostatic pressures up to 10 GPa. Energy-volume and enthalpy-pressure curves were used to determine the phase transition pressures of RVO4 compounds. Among the four compounds examined in both phases, YbVO4 was determined to be less compressible than the other compounds. The computed band structures indicated that RVO4 compounds in both phases are semiconductors with a direct bandgap at the Γ→ Γ point. Optical spectra such as dielectric constants, refractive index, reflectivity, absorption coefficient, birefringence, optical conductivity, and energy loss function were computed as functions of incident radiation energy in the energy range of 0–45 eV. The optical anisotropy of RVO4 compounds was observed in both phases. The computed birefringence values for zircon (scheelite) RVO4 indicate that they are uniaxial positive (negative) crystals and have a large birefringence value. Hydrostatic pressure was found to play an important role in the structural, optical, and electronic properties of both phases of RVO4 compounds.

Theoretical method and experimental verification for solving two/three component phononic crystals based on comsol partial differential equation module

Abstract In order to reduce the low frequency vibration and noise of ships, the phononic crystal structure is used to control the vibration and noise of ships. Based on three-dimensional spatial elastic wave theory and plane wave expansion method, combined with the differential equation module of finite element software, the band structure and transport characteristics of phononic crystal structure can be accurately solved. The correctness and feasibility of this method are verified by comparison with the simulation results of solid mechanics module of finite element software, which provides a new idea for solving phononic crystal structure. It lays a solid foundation for further study of phononic crystal structure. At the same time, this paper studies a new phononic crystal sandwich plate structure, which is applied to the vibration and noise reduction of ships. The theoretical method and experiment are used to study the structure, which proves that the structure has good vibration and noise reduction performance, and further explains the correctness and feasibility of the theoretical method. Based on this calculation method, it can be used to study the effect of the geometrical parameters and material parameters of phononic crystal structure on the band gap. By adjusting these parameters reasonably, the ship can achieve a good effect of vibration and noise reduction.

First-principles calculation of the stopping power of protons in hexagonal boron nitride with different stacking sequences.

The Time-dependent density functional theory was used to calculate stopping power of one and two layers of Hexagonal Boron Nitride (h-BN) with different stacking sequences. The simulation results revealed that stopping power is influenced by collision parameters and electron density, while proton charge state has little effect on stopping power. Additionally, charge transfer and force of protons in h-BN materials were analyzed in detail under different stacking sequences. The calculation results show that although the force on the projectile mainly comes from the target atoms, the limited interaction time allows the projectile to primarily dissipate energy through electron excitation. The influence of the variations in electronic structure due to different stacking structures on the stopping power was investigated. The research results indicate that the dislocation stacking in h-BN, which slightly increases the energy loss, is mainly attributed to the changes in electron density and the role of the impact parameter. This asymmetric stacking structure may have a more pronounced shielding effect on particles. Despite the slight variations in band structures due to different stacking configurations of h-BN, the bandgap widths are roughly consistent, which leads to protons displaying similar energy transfer properties as they pass through bilayer h-BN with varying stackings.&#xD.

Electric Field-Tunable Superconductivity with Competing Orders in Twisted Bilayer Graphene near the Magic Angle.

Superconductivity (SC) in twisted bilayer graphene (tBLG) has been explored by varying carrier concentrations, twist angles, and screening strength, with the aim of uncovering its origin and possible connections to strong electronic correlations in narrow bands and various resulting broken symmetries. However, the link between the tBLG band structure and the onset of SC and other orders largely remains unclear. In this study, we address this crucial gap by examining in situ band structure tuning of a near magic-angle (θ ≈ 0.95°) tBLG device with a displacement field (D) and reveal competition between SC and other broken symmetries. At zero D, the device exhibits superconducting signatures without the resistance peak at half-filling, a characteristic signature with a strong electronic correlation. As D increases, the SC is suppressed, accompanied by the appearance of a resistance peak at half-filling. Hall density measurements reveal that at zero D, SC arises around the van Hove singularity (vHs) from an isospin or spin-valley unpolarized band. At higher D, the suppression of SC coincides with broken isospin symmetry near half-filling with lifted degeneracy (gd ∼ 2). Additionally, as the SC phase becomes weaker with D, vHs shifts to higher fillings, highlighting the modification of the underlying band structure with the applied electric field. These findings, with recent theoretical study on SC in tBLG, highlight the competition, rather than being connected concomitantly, between SC and other orders promoted by broken symmetries.

Correlating the low-temperature photoluminescence with electron transport properties in cerium oxide thin film.

The complex interaction between the intrinsic and extrinsic state variables of strongly correlated insulator thin films is drawing interest as it shows memristive behavior that may be applicable to neuromorphic computing. Cerium oxide is an interesting material as its band structure is modified due to the formation of oxygen vacancy defects. The polaron formation that results from the reduction of the Ce4+ state to the Ce3+ state through oxygen vacancies is crucial for the electron transport in cerium oxide and is strongly influenced by temperature. In this work, we examined the relationship between the change in band structure and the associated conductivity at lower temperatures when ceria is exposed to light. Following light excitation, the creation of oxygen vacancies results in electron localization in the Ce 4f state, followed by the electron transition from 4f1 to 4f0, generating the PL spectra. With decreasing temperature, the lattice vibration decreases, and the splitting in the PL peak at a particular energy state validates the weaker electron-phonon interaction with an exciton trap. This reduces the carrier mobility of the film as observed from the resistance vs temperature curve of ceria under dark conditions. When excited by a particular energy of light, the electrons move more easily from the defect state to the conduction band, increasing conductivity at much lower temperatures than the conductivity under dark conditions.

Direct probing of energy gaps and bandwidth in gate-tunable flat band graphene systems

Moiré systems featuring flat electronic bands exhibit a vast landscape of emergent exotic quantum states, making them one of the resourceful platforms in condensed matter physics. Tuning these systems via twist angle and the electric field greatly enhances our comprehension of their strongly correlated ground states. Here, we report a technique to investigate the nuanced intricacies of band structures in dual-gated multilayer graphene systems. We utilize the Landau levels of a decoupled monolayer graphene to extract the electric field-dependent bilayer graphene charge neutrality point gap. Then, we extend this method to analyze the evolution of the band gap and the flat bandwidth in twisted mono-bilayer graphene. The band gap maximizes at the same displacement field where the flat bandwidth minimizes, concomitant with the emergence of a strongly correlated phase. Moreover, we extract integer and fractional quantum Hall gaps to further demonstrate the strength of this method. Our technique paves the way for improving the understanding of electronic band structures in versatile flat band systems.

Reduction of absorption of Ta2O5 monolayers through the suppression of structural defects by employing an appropriate ionic oxygen concentration

Ultralow-absorption laser films have critical applications in high-power continuous-laser and gravitational-wave-detection systems. During film deposition, the ionic oxygen concentration significantly affects the absorption loss of the film. In this study, Ta2O5 monolayers were deposited using an ion-assisted electron beam evaporation technique, and the weak absorption at 1064 nm, temperature rise, optical band gap, element content, and binding energy were tested and analyzed. The band structure and microdefects of the Ta2O5 films were characterized, and their correlation with the absorption properties was established. The analyses revealed that the primary mechanism responsible for reducing the absorption loss in Ta2O5 films was an appropriate ionic oxygen concentration, which improved the optical band gap and stoichiometric ratio and reduced oxygen vacancy defects. For Ta2O5 monolayers deposited with the optimal ionic oxygen concentration, the weak absorption was approximately 7.2 ppm and the temperature rise was approximately 0.6 °C, 1/4 and 1/3 of the values of those deposited with an excessive concentration, respectively—an important finding in the preparation of ultralow-absorption laser films.

Strong long-wave infrared optical response in a topological semiconductor with a Mexican-hat band structure

Strong long-wave infrared optical response in a topological semiconductor with a Mexican-hat band structure

Electronic band structure of GaN diluted and overdiluted with group-V elements

Electronic band structure of GaN diluted and overdiluted with group-V elements