Semiconductor Phase Research Articles

Correlation between magnetic and electrical properties of the superparamagnetic La0.6Ca0.4MnO3 compound

In this research work, we investigated the correlation between the electrical and magnetic properties of the superparamagnetic compound La0.6Ca0.4MnO3(S0C1) prepared by the citric-gel method. The confrontation of the experimental data with the theoretical models revealed that the conduction at low temperatures, in the ferromagnetic metallic (FMM) phase, can be mainly described by electron–electron (e-e) and electron-magnon (e-m) interactions. The contribution of the (e-m) interaction, became weak for strong magnetic fields. At high temperatures, in the paramagnetic semiconductor (PMSC) phase, the thermally activated hopping (TAH) model proved to be the most appropriate to fit the experimental data. To describe the resistivity behavior in a wide temperature range including the phase transition region between the (FMM) and (PMSC) phases, we adopted the percolation model, based on the phase segregation mechanism.

Reconstructive metal–semiconductor phase transition between nonlayered and layered tungsten dinitride

Reconstructive phase transitions are characterized by significant changes in the crystal structure of a material, typically accompanied by dramatic changes in its physical properties. In this Letter, via first-principles calculations, we report a reconstructive phase transition between nonlayered and layered tungsten dinitride (WN2) with kinetic energy barriers of 0.19 and 0.61 eV per formula unit depending on the transition direction. The nonlayered-to-layered transition can be triggered when an in-plane biaxial strain reaches 9.3%, while the layered-to-nonlayered transition happens at 53.5% of an out-of-plane uniaxial strain. The nonlayered and layered WN2 phases exhibit distinct structural, bonding, and electronic characteristics. Another intrinsic advantage of the reconstructive transition between layered and nonlayered phases is that it can be easily extended to two-dimensional (2D) nanoscale regions. Our results predict a rich phase diagram for 2D WN2 under strains, appealing for advanced nanoelectronics applications such as phase-change electronics or pressure sensors.

Lead-free semiconductor materials with high phase transition temperature: [1-Methylimidazole][SbBr4]

Semiconductor with structure phase change is a special multi-functional material, which plays an important role in the field of Solar Energy, information computing, sensor technology, artificial intelligence, etc. In this paper, the organic–inorganic lead-free semiconductor phase change material [1-Methylimidazole][SbBr4] (1) was successfully constructed. The IR, TGA, DSC, VT-PXRD, solid-state UV–vis spectroscopy and temperature dependence of dielectric constant were characterized and analysed. Single crystal X-ray diffraction shows that at 298 K, the space group is P21/c, the point group 2/m; an endothermic and exothermic peak appeared near 386 K and 367 K in the DSC heating–cooling cycles. Near the corresponding phase transition temperature point, compound 1 exhibits a significant reversible change in the dielectric platform. Interestingly, the band gap of compound 1 is about 2.53 eV. The existence of such interesting physical properties is closely related to the interaction between cations and anions in the molecule and the connection of internal hydrogen bonds. By constructing organic–inorganic hybrid semiconductor materials, we hope to obtain semiconductor materials with phase transition properties and actively explore and provide some ideas and support for the application of new high-tech materials.

Study on the interaction between Mg2C monolayer and VA group trihydrides under strain engineering

The influence of biaxial strain ranging from −5–15 % on the physical properties of Mg2C monolayer was systematically investigated. The study revealed that Mg2C undergoes a phase transition from metallic to semimetallic to semiconducting under varying degrees of strain. This characteristic allows Mg2C to exhibit diverse physical property changes under strain control. Additionally, the adsorption behavior of several toxic group VA trihydride gas molecules (NH3, PH3, AsH3, SbH3) on Mg2C was examined. The results indicate that within a strain range of −5–10 %, Mg2C shows the most significant adsorption effect on NH3, with adsorption energies ranging from −0.9 eV to −5 eV. Strain significantly impacts the physical properties of the adsorption system. All four systems exhibit a semiconductor phase transition within the strain range of 2–3 %. Between 10 % and 12 % strain, the adsorption energy of the four systems increases rapidly. Strains exceeding 12 % induce structural changes in the original crystal structure. This discovery not only supports the application of Mg2C as a gas sensor material but also provides new empirical references for regulating two-dimensional material properties through strain engineering.

Giant Photodegradation Rate Enabled by Vertically Grown 1T/2H MoS2 Catalyst on Top of Silver Nanoparticles

The exaltation of the photodegradation performance of dichalcogenide MoS2 grown on top of silver nanoparticles (Ag‐NPs) is reported on. The fabricated MoS2 nanosheets nucleate vertically from Ag‐NPs seeds, enabling the growth of both metallic and semiconductor phases 1T/2H‐MoS2. Findings reveal remarkable enhancement of the Raman scattering and an exceptional broadband optical absorption attributed to plasmonic effects induced by the presence of both metallic 1T‐MoS2 and Ag‐NPS at 2H‐MoS2 interfaces. To leverage this effect, photodegradation tests are conducted to remove methyl orange pollutant. Notably, results reveal a significant increase in photodegradation efficiency and rate constant, reaching up to 120% and 550% over pristine 2H‐MoS2, respectively. This finding underscores the role of Ag‐NPs and 1T‐MoS2 tandem to unlock the superior photodegradation properties of vertically aligned 2H‐MoS2 toward methyl orange, paving the way for the development of dichalcogenide‐based hybrid photocatalyst for wastewater treatment and environmental remediation.

Heterocontact-Triggered 1H to 1T' Phase Transition in CVD-Grown Monolayer MoTe2: Implications for Low Contact Resistance Electronic Devices.

Single-layer molybdenum ditelluride (MoTe2) has attracted attention due to the smaller energy difference between the semiconducting (1H) and semimetallic (1T') phases with respect to other two-dimensional transition metal dichalcogenides (TMDs). Understanding the phenomenon of polymorphism between these structural phases is of great fundamental and practical importance. In this paper, we report a 1H to 1T' phase transition occurring during the chemical vapor deposition (CVD) synthesis of single-layer MoTe2 at 730 °C. The transformation originates at the heterocontact between monoclinic and hexagonal crystals and progresses to either yield a partial or complete 1H to 1T' phase transition. Microscopic and spectroscopic analyses of the MoTe2 crystals reveal the presence of Te vacancies and mirror twin boundaries (MTB) domains in the hexagonal phase. The experimental observations and theoretical simulations indicate that the combination of heterocontact formation and Te vacancies are relevant triggering mechanisms in the observed transformation. By advancing in the understanding and controlling of the direct synthesis of lateral 1T'/1H heterostructures, this work contributes to the development of MoTe2-based electronic and optoelectronic devices with low contact resistance.

Self‐Encapsulated N‐Type Semiconducting Photoresist Toward Complementary Organic Electronics

AbstractSemiconducting photoresists hold great promise for scale‐up manufacturing of organic field‐effect transistors (OFETs) for integrated organic electronics. While photolithographic p‐type OFETs have achieved a considerable balance among patterning precision, electrical properties and process stability, it remains challenging for n‐type OFETs due to the inherent limited mobility and ambient instability. Herein, a n‐type semiconducting photoresist (SPr) is developed that is compatible with photolithography procedures. By utilizing the solvent‐driven force, a self‐encapsulated blend film with gradient semiconductor phase is prepared, where the underneath transistor active layer is protected by the upper cross‐linked network, avoiding solvent erosion and air doping. As such, a mobility up to 1.1 cm2 V−1 s−1 that is comparable with amorphous Si is achieved, with remained mobility by ≈90% after long‐term exposure to developer and stripper or atmospheric conditions. The sub‐micrometer patterning accuracy of SPr enables the fabrication of organic transistor arrays with a density of 9 × 105 units cm−1, which is comparable to other state‐of‐the‐art devices fabricated by the printing or photolithography, demonstrating immense potential in integrated organic electronics.

Optical and conduction mechanism study of lead-free CsMnCl3 perovskite

Perovskite research is increasingly focused on lead-free, all-inorganic single crystals due to their lower biological toxicity and greater material stability. While lead-based perovskites show promise, their environmental and health risks are concerning. Lead-free alternatives provide a safer, more sustainable option with enhanced durability for practical applications. Nevertheless, this paper presents a structural, optical, and conduction study of lead-free CsMnCl3 perovskite. The material was prepared using slow evaporation method, the obtained compound crystallizes in a hexagonal system with the space group R-3m. The absorption spectrum of CsMnCl3 is analyzed, and the band gap is estimated to be 4.56 eV. The electrical study is crucial for the identification of the allows us to classify CsMnCl3 as a semiconductor, with conductivity increasing with temperature, as expected. The temperature-dependent electrical conductivity (dc) reveals a transition from semiconductor to metallic behavior at 383 K and from metallic to semiconductor behavior at 403 K. The study of the conductivity in the semiconductor phase indicates that above 383 K, the conductivity of CsMnCl3 is governed by a single polaron hopping, and that below 403 K. In summary the comprehensive study of the structural, optical, and electrical properties of CsMnCl3 provides valuable insights into its semiconductor characteristics and charge transport mechanisms, highlighting its potential for sustainable and environmentally friendly applications.

Low-threshold distributed feedback laser based on holographic polymer dispersed liquid crystals through the oriented organic semiconductor films

A specific optimized configuration for low threshold organic semiconductor laser based on a holographic polymer dispersed liquid crystal (HPDLC) transmission grating was demonstrated. Here the organic semiconductor films and phase separated liquid crystal (LC) molecules were oriented along the direction of the HPDLC grating grooves. The influence of the organic semiconductor chain orientation and the excitation polarization on the optical properties of the materials has been investigated. Especially, when polymer chain orientation, LC molecules and pump light polarization are consistent with the direction of the grating grooves, the performance of the outgoing laser is greatly improved. Up to 9.78% conversion efficiency with a threshold lower to 0.12 μJ/pulse can be obtained, indicating their potential for high-performance organic optoelectronics.

Construction of an Ohmic Contact Cathode by Two Metal Sulfides for efficient Capture and Catalysis of Polysulfide.

The slow reaction kinetics and severe shuttle effect of lithium polysulfide make Li-S battery electrochemical performance difficult to meet the demands of large electronic devices such as electric vehicles. Based on this, an electrocatalyst constructed by metal phase material (MoS2) and semiconductor phase material (SnS2) with ohmic contact is designed for inhibiting the dissolution of lithium polysulfide with improving the reaction kinetics. According to the density-functional theory calculations, it is found that the heterostructured samples with ohmic contacts can effectively reduce the reaction-free energy of lithium polysulfide to accelerate the sulfur redox reaction, in addition to the excellent electron conduction to reduce the overall activation energy. The metallic sulfide can add more sulfophilic sites to promote the capture of polysulfide. Thanks to the ohmic contact design, the carbon nanotube-MoS2-SnS2 achieved a specific capacity of 1437.2 mAhg-1 at 0.1 C current density and 805.5 mAhg-1 after 500 cycles at 1 C current density and is also tested as a pouch cell, which proves to be valuable for practical applications. This work provides a new idea for designing an advanced and efficient polysulfide catalyst based on ohmic contact.

Electronic instability in pressured black phosphorus under strong magnetic field

In this paper, we have systematically studied the electronic instability of pressured black phosphorous (BP) under strong magnetic field. We first present an effective model Hamiltonian for pressured BP near the Lifshitz point. Then we show that when the magnetic field exceeds a critical value, the nodal-line semimetal (NLSM) state of BP with a small band overlap re-enters the semiconductive phase by re-opening a small gap. This results in a narrow-bandgap semiconductor with a partially flat valence band edge. Moreover, we demonstrate that above this critical magnetic field, two possible instabilities, i.e. charge density wave phase and excitonic insulator (EI) phase, are predicted as the ground state for high and low doping concentrations, respectively. By comparing our results with the experiment (Sun et al 2018 Sci. Bull. 63 1539), we suggest that the field-induced instability observed experimentally corresponds to an EI. Furthermore, we propose that the semimetallic BP under pressure with small band overlaps may provide a good platform to study the magneto-exciton insulators. Our findings bring the first insight into the electronic instability of topological NLSM in the quantum limit.

Excess noise and thermoelectric effect in magnetron-sputtered VO2 thin films

This work presents the excess noise and thermoelectric (Seebeck) measurements on polycrystalline vanadium dioxide (VO2) thin films. Noise spectral power density (SPD) of current fluctuations in the semiconducting (SC) phase had a typical flicker noise (f−γ) characteristic with an average slope parameter γ of 1.13. Normalized SPD (Sn) values obtained in the SC-phase indicate that the noise originates in the bulk of the film. On the contrary, in the metallic (M)-phase, γ values were greater than unity, and the observed Sn values indicated that the origin of the noise is most likely from the contacts or surface rather than the bulk. A general decrease was observed in Sn by a factor of 4–5 from the SC- to M-phase. Moreover, Sn in the SC-phase showed no temperature dependence. An interpretation based on the number of charge carrier fluctuations in Hooge's model led to an unrealistically high Hooge parameter and had to be ruled out. We propose that the fluctuations are related to the mobility fluctuations of carriers arising primarily from grain-boundary scattering which explains the observed characteristics well. The Seebeck coefficients (S) obtained under both heating and cooling schedules showed the n-type nature of magnetron-sputtered VO2 films in the SC-phase. Differently, in the M-phase, the S value was positive. The S values obtained from the cooling schedule signified the low percolation threshold of the metal-to-insulator transition already demonstrated for VO2 thin films grown on r-cut sapphire using the Efros–Shklovskii percolation model.

Solvethermal synthesis and thermochromic properties of CaF2@VO2-based core-shell structure composites

Vanadium oxide (VO2)-based core-shell structures exhibit unique properties due to their reversible metal–insulator transition (MIT). As a result, numerous applications on the device level have been reported in the literature. However, since VO2 are multivalent compounds, the controllable preparation of VO2 core-shell-based particles is quite challenging. Along these lines, in this work, to overcome these limitations, the growth mechanism of VO2 shells on spherical substrates was systematically investigated. More specifically, the CaF2@VO2 core-shell microspheres were fabricated successfully by applying the solvent/hydrothermal-calcination method for the first time, while the phase evolution and morphological characteristics of the preparation process were studied in detail. From the obtained results, it was demonstrated that the composite particle's morphology and phase structure strongly depend on the activator, solvent, annealing atmosphere, and the annealing temperature. In addition, the infrared transmittance of the prepared CaF2@VO2(M) coating exhibited a decrease of 34.08 % during the metal–semiconductor phase transition in the 4–12 μm wavelength. Compared with the VO2 coatings and the uncoated CaF2/VO2 coatings, the transmittance conversion performance (ΔT) of the CaF2@VO2(M) coating was also increased by 22.62 % and 21.22 %, respectively.

Machine-Learning-Based Interatomic Potentials for Group IIB to VIA Semiconductors: Toward a Universal Model.

Rapid advancements in machine-learning methods have led to the emergence of machine-learning-based interatomic potentials as a new cutting-edge tool for simulating large systems with ab initio accuracy. Still, the community awaits universal interatomic models that can be applied to a wide range of materials without tuning neural network parameters. We develop a unified deep-learning interatomic potential (the DPA-Semi model) for 19 semiconductors ranging from group IIB to VIA, including Si, Ge, SiC, BAs, BN, AlN, AlP, AlAs, InP, InAs, InSb, GaN, GaP, GaAs, CdTe, InTe, CdSe, ZnS, and CdS. In addition, independent deep potential models for each semiconductor are prepared for detailed comparison. The training data are obtained by performing density functional theory calculations with numerical atomic orbitals basis sets to reduce the computational costs. We systematically compare various properties of the solid and liquid phases of semiconductors between different machine-learning models. We conclude that the DPA-Semi model achieves GGA exchange-correlation functional quality accuracy and can be regarded as a pretrained model toward a universal model to study group IIB to VIA semiconductors.

Novel phase of the Na-N system in the N-rich region under high pressure

The study of the Na-N system in the N-rich region under high pressure enriches the structural types of polynitrogen structure: four novel structures (P1-NaN7, Cm-NaN7, C2-NaN8, and R 3‾-NaN8) are proposed. The layered structure of the Cm-NaN7 and R 3‾-NaN8 phase consisting of the N16 and N18 ring respectively are first proposed in the Na-N system under high pressure. The Cm-NaN7 and R 3‾-NaN8 phase not only can be stabilized to the ambient conditions, but also the Cm-NaN7 phase can decompose and release energy at 325 K, while the R 3‾-NaN8 phase can be stable to at least 1000 K. The research shows that the different decomposition barriers and charge transfer are important reasons for the difference of decomposition temperature. The Cm-NaN7 phase is semiconductor phase with a band gap of 0.06 eV, while the R 3‾-NaN8 phase is metal phase. Furthermore, the excellent energy density, detonation pressure, and detonation velocity of the Cm-NaN7 and R 3‾-NaN8 phase make them as potential candidates in the application of high energy density materials.

Recent Progress in Polysaccharide-Based Materials for Energy Applications: A Review.

In recent years, polysaccharides have emerged as a promising alternative for the development of environmentally friendly materials. Polysaccharide-based materials have been mainly studied for applications in the food, packaging, and biomedical industries. However, many investigations report processing routes and treatments that enable the modification of the inherent properties of polysaccharides, making them useful as materials for energy applications. The control of the ionic and electronic conductivities of polysaccharide-based materials allows for the development of solid electrolytes and electrodes. The incorporation of conductive and semiconductive phases can modify the permittivities of polysaccharides, increasing their capacity for charge storage, making them useful as active surfaces of energy harvesting devices such as triboelectric nanogenerators. Polysaccharides are inexpensive and abundant and could be considered as a suitable option for the development and improvement of energy devices. This review provides an overview of the main research work related to the use of both common commercially available polysaccharides and local native polysaccharides, including starch, chitosan, carrageenan, ulvan, agar, and bacterial cellulose. Solid and gel electrolytes derived from polysaccharides show a wide range of ionic conductivities from 0.0173 × 10-3 to 80.9 × 10-3 S cm-1. Electrodes made from polysaccharides show good specific capacitances ranging from 8 to 753 F g-1 and current densities from 0.05 to 5 A g-1. Active surfaces based on polysaccharides show promising results with power densities ranging from 0.15 to 16 100 mW m-2. These investigations suggest that in the future polysaccharides could become suitable materials to replace some synthetic polymers used in the fabrication of energy storage devices, including batteries, supercapacitors, and energy harvesting devices.

Extraordinary Polarization and Thickness Dependences of Photocarrier Dynamics in PdSe2 Ribbons.

Pentagonal palladium diselenide (PdSe2) stands out for its exceptional optoelectronic properties, including high carrier mobility, tunable bandgap, and anisotropic electronic and optical responses. Herein, we systematically investigate photocarrier dynamics in PdSe2 ribbons using polarization-resolved optical pump-probe spectroscopy. In thin PdSe2 ribbons with a semiconductor phase, the photocarrier dynamics are found to be dominated by intraband hot-carrier cooling, interband recombination, and the exciton effect, showing weak crystalline orientation dependences. Conversely, in thick semimetal-phase PdSe2 ribbons, the photocarrier relaxations governed by the electron-optical/acoustic phonon scattering strongly depend on the sample orientation, albeit with a degradation in in-plane anisotropy following hot-carrier cooling. Furthermore, we analyze the correlations between photocarrier dynamics and anisotropic energy dispersions of electronic structures across a wide range in k space, as well as the contributions from the anisotropic electron-phonon couplings. Our study provides crucial insights for developing polarization-sensitive photoelectronic devices based on PdSe2.

Structure relations with transport properties in p-type thermoelectric materials: Iron silicides

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe1-xMnxSi2 (0≤x≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe2Si5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi2) through heat treatment. The amount of β-FeSi2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (nH of holes) but decrease the mobility (μH). By substituting Mn to β-FeSi2, the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties.

Hypersensitized electrochemical sensing of Hg(II) based on phase engineering of Co doped MoSe2 nanosheets: Insight in dynamic phase change induced by the chemical interaction between Se and Hg(II)

Transition metal dichalcogenides (TMDs) are regarded as promising nanomaterials for electrochemical detection to heavy metal ions due to their variable performance. However, their detection performances are still limited by inferior conductivities and adsorption ability. In this work, the defects and phase engineering strategy are proposed to utilize cobalt (Co) doped MoSe2 nanosheet for electrochemical detection of Hg ion (Hg(II)). Through Co doping, we successfully achieved the phase transition of MoSe2 from the 2 H phase of semiconductor to the 1 T phase of conductor. Moreover, the 1 T MoSe2 is demonstrated to show a better adsorption and catalytic ability for Hg(II) detection than that of 2 H MoSe2. As a result, the MoSe2 containing atomic ratio of Co is 10% (named CM10) owning suitable content of 1 T phase has a superior sensitivity of 52.17 μA μM−1 and a low LOD of 3.96 nM for Hg(II). More importantly, combining with the characterization of X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) calculation, it is found that the Hg(II) adsorption will also lead to the phase change of MoSe2, and the change state in the samples after the adsorption of Hg(II) will be more accurate to be responsible for the improvement of catalytic ability.

Regulating the crystal phase of bismuth-based semiconductors for promoted photocatalytic performance

Regulating the crystal phase of bismuth-based semiconductors for promoted photocatalytic performance