Metal Semiconductor Research Articles

Constructing Built-In Electric Fields with Semiconductor Junctions and Schottky Junctions Based on Mo–MXene/Mo–Metal Sulfides for Electromagnetic Response

HighlightsMo–MXene/Mo–metal sulfides with semiconductor junctions and Mott–Schottky junctions are designed.Built-in electric field are constructed in semiconductor–semiconductor–metal heterostructure, enhancing dielectric polarization and impedance matching.Density functional theory calculations and Radar cross-section simulations confirmed the excellent electromagnetic wave absorption ability of heterostructures.

Observation of 2D-magnesium-intercalated gallium nitride superlattices

Since the demonstration of p-type gallium nitride (GaN) through doping with substitutional magnesium (Mg) atoms1,2, rapid and comprehensive developments, such as blue light-emitting diodes, have considerably shaped our modern lives and contributed to a more carbon-neutral society3–5. However, the details of the interplay between GaN and Mg have remained largely unknown6–11. Here we observe that Mg-intercalated GaN superlattices can form spontaneously by annealing a metallic Mg film on GaN at atmospheric pressure. To our knowledge, this marks the first instance of a two-dimensional metal intercalated into a bulk semiconductor, with each Mg monolayer being intricately inserted between several monolayers of hexagonal GaN. Characterized as an interstitial intercalation, this process induces substantial uniaxial compressive strain perpendicular to the interstitial layers. Consequently, the GaN layers in the Mg-intercalated GaN superlattices exhibit an exceptional elastic strain exceeding −10% (equivalent to a stress of more than 20 GPa), among the highest recorded for thin-film materials12. The strain alters the electronic band structure and greatly enhances hole transport along the compression direction. Furthermore, the Mg sheets induce a unique periodic transition in GaN polarity, generating polarization-field-induced net charges. These characteristics offer fresh insights into semiconductor doping and conductivity enhancement, as well as into elastic strain engineering of nanomaterials and metal–semiconductor superlattices13.

Charge Transport Approaches in Photocatalytic Supramolecular Systems Composing of Semiconductor and Molecular Metal Complex for CO2 Reduction.

The design of photocatalytic supramolecular systems composing of semiconductors and molecular metal complexes for CO2 reduction has attracted increasing attention. The supramolecular system combines the structural merits of semiconductors and metal complexes, where the semiconductor harvests light and undertakes the oxidative site, while the metal complex provides activity for CO2 reduction. The intermolecular charge transfer plays crucial role in ensuring photocatalytic performance. Here, we review the progress of photocatalytic supramolecular systems in reduction of CO2 and highlight the interfacial charge transfer pathways, as well as their state-of-the-art characterization methods. The remaining challenges and prospects for further design of supramolecular photocatalysts are also presented.

Metal–semiconductor transition in bilayer graphene by bowl inversion of monofluorosumanene

The bowl-shaped hydrocarbon molecule, monofluorosumanene (C21H11F), can act as a molecular switch to control the carrier density of bilayer graphene by flipping its conformation. Our calculations indicate that monofluorosumanene, in which F atom is located outside the curved C–C network (exo-F molecular conformation), induces electron and hole co-doping of 1.5 × 1013 cm−2 in monofluorosumanene-intercalated bilayer graphene because of a large dipole moment normal to the molecular plane of the monofluorosumanene. The intercalated monofluorosumanene does not affect the electronic structure of bilayer graphene when the F atom is located inside the curved C–C network (endo-F conformation) owing to a small out-of-plane dipole moment. The application of an external electric field across the graphene layers promotes bowl inversion between endo-F and exo-F molecular conformations because of the low activation barrier (approximately 800 meV) between these two conformations and the dipole moment normal to the molecular plane of the exo-F conformation.

The electrical and dielectric features of Al/YbFeO3/p-Si/Al and Al/YbFe0.90Co0.10O3/p-Si/Al structures with interfacial perovskite-oxide layer depending on bias voltage and frequency

In this investigation, thin films of YbFeO3, both in its pure form and doped with 10% Co, were fabricated on a p-Si substrate at 500 °C through the radio-frequency magnetron sputtering method. Examination via Scanning Electron Microscopy demonstrated a porous texture for the pure sample, contrasting with a smooth and crack-free surface post-Co doping. Analysis via X-ray photoelectron spectroscopy unveiled Yb’s 3 + oxidation state, alongside the presence of lattice oxygen, oxygen vacancies, and adsorbed oxygen evident in Gaussian fitting curves. Photoluminescence spectroscopy revealed an augmented emission intensity, likely attributed to increased defect initiation in the Co-doped specimen. Moreover, Raman spectroscopy was employed to identify vibration modes in the examined samples, demonstrating shifts in Raman peaks indicative of Co substitution and subsequent distortion in the crystal structure of YbFeO3. Electrical assessments were conducted at room temperature (300 K) under ambient conditions, employing voltage and frequency as variables. Capacitance–voltage measurements illustrated the emergence of an accumulation, with depletion and inversion regions manifesting at different frequencies based on the applied voltage, attributed to the YbFeO3 interfacial layer at the Al and p-Si interface. The conductance-voltage characteristics indicated that the structure exhibited maximum conductance in the accumulation region. Series resistance for these configurations was deduced from capacitance-conductance-voltage measurements, indicating a dependence on both bias voltage and frequency. The doping process led to a reduction in capacitance and series resistance, accompanied by an increase in conductance values. After obtaining corrected capacitance and conductance parameters, it became evident that series resistance significantly influences both parameters. Interface state density (Nss), determined through the Hill-Coleman relation demonstrated a decreasing trend with increasing frequency. The pure sample exhibited higher interface state density compared to the Co-doped sample at each frequency, highlighting that the 10% Co-doped YbFeO3 thin film enhances the quality of the metal–semiconductor interface properties compared to the pure contact.

Plasma-modulated supercapacitive-coupled memristive behavior of two-dimensional gallium oxide channels towards the realization of tunable semiconductor–metal nanoelectronic gates

This study explores the opportunities of plasma treatment of ultra-thin metal-oxide films to enable the design of 2D electronic channels with tunable charge storage/transfer characteristics. The plasma treatment enabled the nanoengineering of 2D Ga2O3 films. Study revealed that various plasma treatments altered the electronic characteristics of 2D Ga2O3, finally enabling the realization of supercapacitive-coupled memristive behavior of 2D structures. The c-AFM studies of 2D Ga2O3/Au hybridinterfaces, showed the evolution from zero I-V hysteresis loops to non-zero hysteresis loops. The plasma treatment of 2D films enabled the transition from capacitor-like behavior resembling nanobattries (Ar Plasma) to faradic pseudocapacitance/supercapacitive (Cl plasma) and, finally, to resistive-switching memristive behavior (SO2 plasma). Notably, the high specific capacitance of 113F.g−1 was achieved at the current density of 2.6 A.g−1 in the Ar + Cl plasma modified 2D Ga2O3 films. Moreover, the supercapacitive-coupled memristive properties of the 2D Ga2O3/Au hybrid interfaces facilitated the development of synapse-mimetic 2D electronic gates with adjustable retention characteristics. The electronic channel demonstrated the ability to emulate the depolarization characteristics of synaptic nodes, enabling the consistent reception and memorization of informative electrical signals. This was achieved with an energy consumption of 0.4 nJ per synaptic event at a frequency of 100 KHz.

Anisotropic growth of gold anchors on CdSe semiconductor quantum platelets for self-assembled architectures with well-connected electronic circuits for the electrochemical detection of enrofloxacin.

Anisotropic growth of nanomaterials enables advances in building diverse and complex architectures, which exhibit unique properties and enrich the choice of nano-building modules for electrochemical sensor devices. Herein, an anisotropic growth method was proposed to anchor gold nanoparticles (AuNPs) onto both ends of quasi-two-dimensional CdSe semiconductor quantum nanoplatelets (NPLs), appearing with a monodisperse and uniform nano-dumbbell shape. Then, these AuNPs were exploited as natural anchor points and further initiated self-assembly to create complex architectures via dithiol bridges. Detailed studies illustrated that the covalent Se-Au bonds facilitate effective charge transfer in the internal metal-semiconductor (M-S) electric field. The narrowed energy gap and up-shifted highest occupied molecular orbital were favored for electron removal during the electro-oxidation process. The ultrathin CdSe NPLs supplied a large specific surface area, carrying remaining holes and abundant active sites for target electro-catalysis. As a result, using the assembled complex as the electrode matrix with well-connected electronic circuits, a reliable electrochemical sensor was achieved for enrofloxacin detection. Under the optimal conditions, the current response exhibits two linear dynamic ranges, 0.01-10.0 μM and 10.0-250 μM, and the detection limit was calculated as 0.0026 μM. This work not only opens up broad application prospects for heterogeneous M-S combinations as effective electrochemical matrixes but also develops reliable antibiotic assays for food and environmental safety.

Synthesis and Physical Properties of the Misfit Layered Compound (EuS)1.13(NbSe2)2.

A new misfit layered compound with the stoichiometry (EuS)1+δ(NbSe2)2 (δ ≈ 0.13) has been successfully synthesized. High-resolution transmission electron microscopy and powder X-ray diffraction confirm the misfit structure with (EuS)-(EuS) spacing of 18.30(1) Å. Magnetization, electrical resistivity, heat capacity, and thermal transport measurements show that the material is a heavily doped semiconductor or poor metal with a low thermal conductivity of ∼1 W/m K and an antiferromagnetic ordering transition at TN = 4.7 K. In contrast to the parent materials, the misfit is neither ferromagnetic nor superconducting down to T = 0.4 K. We find evidence of a field-driven transition to a ferromagnetic state due to reorientation of ferromagnetic EuS layers at μoH = 0.5 T at T = 2 K.

Enhanced self-powered metal–semiconductor–metal WSe2 photodetectors with asymmetric Schottky contacts through tailored electrode thickness and positioning

Enhanced self-powered metal–semiconductor–metal WSe2 photodetectors with asymmetric Schottky contacts through tailored electrode thickness and positioning

Potential-dependent photo-electro-catalysis coupling mechanism for methanol oxidation: A case study over Pt/Cu-Nb2O5 nanorod arrays

The sluggish methanol oxidation kinetics has seriously hindered the development of direct methanol fuel cells. Photo-electro-catalysis is expected to accelerate reaction rates, yet suffers from lack of efficient photoelectrocatalysts and more importantly, less understanding on photo-electro-catalysis mechanism. Herein, a unique Cu-Nb2O5 nanorod array with excellent light adsorption and charge transfer ability, on which supports Pt nanoparticles, is constructed for photo-electrocatalytic methanol oxidation reaction (MOR). Systematical investigation discovers a potential-dependent photo-electro-catalysis coupling mechanism, i.e., at lower potential bias where the Fermi level of semiconductor (Ef,s) is beyond the Fermi level of Pt (Ef,Pt), electrons transferring from Pt to semiconductor is switched off, so semiconductor Cu-Nb2O5 alone takes a dominant role for both methanol and water activation; at higher potential bias where Ef,s is below Ef, Pt, electrons flowing from Pt to semiconductor is switched on, so methanol dehydrogenation on Pt surface is allowed energetically. Further investigation on the MOR processes prompts us to propose a MOR pathway that methanol dehydrogenates on Pt surface, with the aid of *OH from the photo-activated water on Cu-Nb2O5 to proceed via formaldehyde, formic acid to carbon dioxide, resulting to a low apparent activation energy and fast kinetics of MOR as compared to its counterpart Pt/Nb2O5. This work not only provides an efficient photoelectrocatalyst for methanol oxidation, but also sheds lights on the underlying photo-electro-catalysis coupling mechanism over semiconductor–metal catalysts.

Comparison of Electrical Conductivity and Schottky Behavior of 4‐[2‐(9‐anthryl)vinyl]pyridine Based Two 1D Coordination Polymers of Zn(II) and Cd(II)

AbstractWith the increase in demand of electronic devices in the modern civilization, research in material science is being projected to grow in faster rate. In this facet, coordination polymer (CP) based electronic device is one of the promising candidates to the material researchers. Herein, two new Zn(II) and Cd(II) based one‐dimensional (1D) CPs, denoted as [Zn(4‐avp)2(5‐nip)] ⋅ (solvent)x (1) and [Cd(4‐avp)(5‐nip)(CH3OH)] (2) have been synthesized using relatively less explored highly conjugated polycyclic aromatic hydrocarbon (PAH) based monodentate ligand, 4‐[2‐(9‐anthryl)vinyl]pyridine (4‐avp) and bidentate linker 5‐nitroisophthalic acid (H25‐nip). In this instance, the CP 1 creates 1D chain polymer, while CP 2 is made up with 1D ladder polymer. It is interesting to note that both the CPs exhibit semiconducting nature and generate metal‐semiconductor (MS) junction Schottky barrier diodes (SBDs). However, Cd‐based CP 2 shows higher charge transport as compared to Zn‐CP 1, which could be due to stronger π⋅⋅⋅π contacts as well as larger size of Cd metal in CP 2. The experimental results are well corroborated with theoretical density of states (DOS) calculations.

Triply degenerate semimetal PtBi2 as van der Waals contact interlayer in two-dimensional transistor

The low-energy electronic excitations in topological semimetal yield a plethora of a range of novel physical properties. As a relatively scarce branch, the research of triple-degenerate semi-metal is mostly confined to the stage of physical properties and theoretical analysis, there are still challenges in its practical application. This research showcases the first application of the triply degenerate semimetal PtBi2 in electronic devices. Leveraging a van der Waals transfer method, PtBi2 flakes were used as interlayer contacts for metal electrodes and WS2 in transistors. The transistor achieved a switching ratio above 106 and average mobility can reach 85 cm2V−1 s−1, meeting integrated circuit requirements. Notably, the excellent air stability of PtBi2 simplifies the device preparation process and provides more stable device performance. Transfer process reduces the Schottky barrier between metal electrodes and semiconductors while avoiding Fermi pinning during metal deposition to achieve excellent contact. This groundbreaking work demonstrates the practical applicability of PtBi2 in the field of electronic devices while opening new avenues for the integration of novel materials in semiconductor technology, setting a precedent for future innovations.

Resistor-to-Schottky barrier analytical model for ohmic contact test structures

Analytical models for investigating Metal–Semiconductor (M–S) ohmic contacts in test structures have conventionally included resistive-only contact interfaces. Given that M–S contacts are fundamentally governed by electron tunnelling across the potential energy barrier at the M–S interface, this simplified approach may result in misinterpretation. This paper describes, in detail, a novel Resistor-to-Schottky (RSB) barrier analytical model that enables a more in-depth exploration of the physics underlying ohmic contacts. The proposed model is analysed and compared with models constructed using the semiconductor device simulator tool TCAD. The study reveals significant differences in outcomes when employing the RSB model rather than the conventional Transmission Line model and contributes to a more comprehensive understanding of M–S ohmic contacts in test structures.

EM and CT synergistic SERS enhancement in Si/TiO2/Ag heterostructures via local interfacial effect

The Si/TiO2/Ag heterostructures with high SERS sensitivity were prepared by sol–gel and electrochemical self-assembly. The electromagnetic (EM) and charge transferring (CT) synergistic mechanism for SERS enhancement was explored by FDTD. The “localized interfacial effect (LIE)” of metal–semiconductor heterostructures can result in the CT between them and the charge carriers’ redistribution, which can facilitate the probe molecules’ adsorption and generate the 3D volume-enhancement of electromagnetic fields, therefore improve the SERS performance effectively. Furthermore, the morphology of Ag was flexibly regulated by changing the applied voltage, and the optimal SERS performance was achieved. With the R6G as a probe molecule, the ultra-low concentration of 10-13 M can be detected. The EF is estimated to be about 1.75 × 1011, and the RSD is about 4.3 %. The photocatalytic effect of Si/TiO2/Ag heterostructure can realize the SERS substrates’ UV self-cleaning and recyclable use with high stability.

Growth of Quasi-Two-Dimensional CrTe Nanoflakes and CrTe/Transition Metal Dichalcogenide Heterostructures

Two-dimensional (2D) van der Waals layered materials have been explored in depth. They can be vertically stacked into a 2D heterostructure and represent a fundamental way to explore new physical properties and fabricate high-performance nanodevices. However, the controllable and scaled growth of non-layered quasi-2D materials and their heterostructures is still a great challenge. Here, we report a selective two-step growth method for high-quality single crystalline CrTe/WSe2 and CrTe/MoS2 heterostructures by adopting a universal CVD strategy with the assistance of molten salt and mass control. Quasi-2D metallic CrTe was grown on pre-deposited 2D transition metal dichalcogenides (TMDC) under relatively low temperatures. A 2D CrTe/TMDC heterostructure was established to explore the interface’s structure using scanning transmission electron microscopy (STEM), and also demonstrate ferromagnetism in a metal–semiconductor CrTe/TMDC heterostructure.

Achieving Room-Temperature ppb-Level H2S Detection in a Au-SnO2 Sensor with Low Voltage Enhancement Effect.

Although semiconductor metal oxide-based sensors are promising for gas sensing, low-power and room temperature operation (24 ± 1 °C) remains desirable for practical applications particularly considering the request of energy saving or net zero emission. In this study, we demonstrate a Au/SnO2-based ultrasensitive H2S gas sensor with a limit of detection (LOD) of 2 ppb, operating at very low voltages (0.05 to 0.5 V) at room temperature. The Au/SnO2-based sensor showed approximately 7 times higher response (the ratio of change in the current to initial current) of ∼270% and 4 times faster recovery (126 s) compared to the pure SnO2-based sensor when exposed to 500 ppb H2S gas concentration at 0.5 V operating voltage at relative humidity (RH) 17.5 ± 2.5%. The enhancement can be attributed to the catalytic characteristics of AuNPs, increasing the number of adsorbed oxygen species on sensing material surfaces. Additionally, AuNPs aid in forming flower-petal-like Au/SnO2 nanostructures, offering a larger surface area and more active sites for H2S sensing. Moreover, at low voltage (<1 V), the localized dipoles at the Au/SnO2 interface may further enhance the absorption of polar oxygen molecules and hence promote the reaction between H2S and oxygen species. This low-power, ultrasensitive H2S sensor outperforms high-powered alternatives, making it ideal for environmental, food safety, and healthcare applications.

Time-resolved Response Improvement of Oxygen-doped a-In–Ga–Sn–O Metal–Semiconductor–Metal Photodetectors by Sputtering

Time-resolved Response Improvement of Oxygen-doped a-In–Ga–Sn–O Metal–Semiconductor–Metal Photodetectors by Sputtering

Heteroepitaxial growth of Ga2O3 thin films on nickel-nanodot-induced buffer layers for solar-blind ultraviolet photodetector applications

Heteroepitaxial growth of gallium oxide (Ga2O3) thin films has been conducted on nickel (Ni)-nanodot-induced buffer layers using a mist chemical vapor deposition. The separation degree and droplet size of the Ni nanodots on sapphire substrates were controlled through a thermal annealing process, thereby being used as templates for the Ga2O3 thin-film growth. The growth of the inverted cone-shaped ε-Ga2O3 polymorph was observed on the nanodots while the α-Ga2O3 polymorph was grown on the sapphire substrate without nanodots, ultimately a thin film with a mixture of ε and α polymorphs can be achieved. By comparing photoresponses of metal–semiconductor–metal photodetectors fabricated on the thin film with the mixed polymorphs and on a single-crystalline α-Ga2O3 film, a promising template for using solar-blind photo-detecting applications has been verified.

Unraveling Exciton-Plasmon Coupling and the PIRET Mechanism in Decorated Silicon Nanowires.

Exciton-plasmon coupling is a fascinating physical phenomenon that has been investigated in various metal semiconductor systems. Intentionally chosen silicon nanowires (SiNWs) systems act as a host material for providing exciton as well as silicon oxide as a thin dielectric. A clear blue-shift in photoluminescence (PL) peak and a significant increase in visible range absorption were observed for metal nanoparticle (MNP) decorated SiNWs (D-SiNWs) which signifies the presence of exciton-plasmon coupling. A further investigation reveals that the possibility of the occurrence of the plasmon-induced resonance energy transfer (PIRET) mechanism is higher. The PL intensity enhancement in Au-decorated SiNWs is higher (∼38 times) in comparison to that in Pt due to the presence of a strong and localized electric field of plasmons near the interface of metal and semiconductors. Moreover, splitting in PL for gold-decorated SiNWs might be due to the presence of dipole-quadrupole coupling along with dipole-dipole coupling, which further increases the strength of the PIRET mechanism.

Gate-controlled spin injection polarity in 2D transistors with Schottky barrier

In 2D semiconductors, the Schottky barrier formed at the metal–semiconductor interface plays a crucial role in controlling electron and spin injection. To explore the spin injection mechanism under gate control, we study MoS2 coupled to ferromagnetic metals. We introduce a spin drift diffusion model which is applicable to the Schottky contact. In this system, the current passing through the Schottky barrier can be larger for the minority spin than for the majority spin due to the tunnel effect. We observe a polarity switching in spin injection with gate voltage variation when the conduction band bottom of the minority spin ferromagnetic metal is closely aligned with the Fermi level. Our results also suggest the spin injection efficiency can be tuned by gate control for half-metals.