High Carrier Mobility Research Articles

Van der Waals epitaxial growth of two-dimensional non-layered [formula omitted] for high-sensitivity [formula omitted] detection

Two-dimensional (2D) materials are considered as ideal building blocks for constructing new functional gas-sensitive devices because of their large specific surface area, abundant active sites and high carrier mobility. However, research has mainly focused on 2D layered materials due to their easy availability. This work aims to further explore the application value of 2D non-layered materials in gas sensing. Firstly, van der Waals epitaxial growth of 2D non-layered CdS1-xSex on fluorophlogopite substrate was achieved by APCVD. Secondly, the CdS1-xSex-based gas sensor exhibits high sensitivity (626 % at 50 ppm NH3), low detection limit (1 ppm), fast response (12 s at 50 ppm NH3), good selectivity and repeatability to NH3 at room temperature. Notably, the sensing performance of the ternary CdS1-xSex for NH3 is better than other structures of binary CdS. This phenomenon is also further explained. Finally, density functional theory is used to calculate the adsorption energy and charge transfer properties, and the results reconfirm that CdS1-xSex is a promising NH3 sensing material. This work provides a universal synthesis method of 2D non-layered alloy materials, and explores the application of 2D CdS1-xSex in gas sensing for the first time, hoping to bring new ideas for the research of other 2D non-layered materials.

In-silico realization of YX (X = N, P, As) pnictide monolayers as highly efficient thermoelectric materials

Exploiting the changes in the electronic and vibrational properties accompanying the reduction of dimensionality from 3D to 2D has now become a widely established strategy for developing materials breaking the figure of merit (ZT) ∼ 1 barrier that was experienced in much of the last century. Several studies have suggested the possibility of developing rare earth pnictides into a new family of prospective thermoelectric (TE) materials owing to the strong p-d hybridization in these materials, leading to dispersive band edges and, consequently, high carrier mobilities in these semiconductors. Motivated by the above developments, we explored the electronic and transport properties of three yttrium pnictide monolayers. We present a detailed investigation highlighting the merit of YX (X = N, P, As) monolayer-based materials for TE applications. We found a high power factor for p-type (n-type) YX monolayers in the y-direction (x-direction). This, in conjunction with low to moderate lattice thermal conductivities 3.335, 1.779, and 1.648 Wm-1K-1 of the YN, YP, and YAs monolayers, respectively, at 500 K, leads to high ZTs in optimally doped YN, YAs and YP of 2.02, 1.39, and 1.18. The finding of high TE performance adds further evidence in support of the conjecture that dimensionality reduction in semiconducting materials with strong p-d hybridization can lead to particularly high electrical conductivities (reaches up to 217.84 × 106 Ω-1m-1 for YN), thereby resulting in excellent ZT. The high TE performance of these materials at 500 K suggests the prospect of developing rare-earth-based materials for energy applications.

Graphene Oxide-Doped Indium Oxide Buffer Film Sandwiched between Titanium Oxide Layers for the Development of Photosensitive Resistive Memory Devices.

Over the past decade, metal oxide semiconductors have attracted considerable attention because of their transparency, high intrinsic charge carrier mobility, and charge carrier density. Metal oxide semiconductors also provide a promising route to develop resistive memory devices because of the tunability of their conductivity via the removal of oxygen ions, forming oxygen vacancies that can act as electron donors. Here, this paper reports the fabrication of a resistive random-access memory (ReRAM) device with TiO2 and TiO2-x layers and introduces a solution-processed In2O3-graphene oxide (GO) buffer layer from a water-based precursor solution to tune the switching characteristics. The devices were compared with a ReRAM device with no buffer layer, and the device composition was optimized by tuning the GO concentration in the layers. The devices showed hysteresis under cyclically scanned bias between positive and negative voltages with clear switching between the low resistance state (LRS) and the high resistance state (HRS). The optimized device also showed a more than 3 orders of magnitude difference in resistance between the LRS and HRS and a stable current retention. The devices also showed photoresponsive behaviors. In the LRS, the current increased significantly under illumination, while in the HRS, the current deteriorated slowly when constantly illuminated. These results highlight the dual role of the GO flakes in the buffer layer by increasing the resistance in the HRS and providing a photoresponsive switching capability. The ReRAM device was connected to a TFT device, and its feasibility as a memory component in a digital circuit was successfully demonstrated. These results provide a new avenue for developing metal-oxide-based ReRAM devices with GO-containing active layers.

Two-Dimensional Pentagonal Materials with Parabolic Dispersion and High Carrier Mobility.

Materials with high carrier mobility, represented by graphene, have garnered significant interest. However, the zero band gap arising from linear dispersion cannot achieve an ideal on-off ratio in field-effect transistors (FETs), limiting practical applications in certain fields. In contrast, parabolic dispersion usually exhibits extremely high carrier mobility and an appropriate band gap. In this work, we predicted a planar pentagonal lattice composed entirely of pentagons (namely penta-MX2 monolayer), where M = Ni, Pd and Pt, X = group V elements. Using first-principles calculations, we demonstrated a parabolic dispersion within this framework, which results in intriguing phenomena, such as a direct band gap (0.551-1.105 eV) and extraordinary high carrier mobility. For penta-MX2 monolayer, the carrier mobility can attain ~1 × 108 cm2 V-1 s-1 (PBE), surpassing those of black phosphorene, graphene and 2D hexagonal materials. This monolayer also displays anisotropic mechanical properties and significant absorption peaks in the ultraviolet spectrum. Remarkably, 2D penta-MX2 monolayers are promising for successful experimental exfoliation, particularly when X is a nitrogen element, opening up new possibilities for designing two-dimensional semiconductor materials characterized by high carrier mobility.

Dual-functional high-crystalline 3D core-shell hexagonal tubular sulfur-doped carbon nitride for enhanced photocatalytic H2 production and simultaneously pollutants degradation

The use of semiconductor photocatalytic technology for water splitting to produce H2 and degrade pollutants is a mild approach for clean energy conversion and environmental water purification. However, the rational design of photocatalysts with high carrier mobility remains a challenge. Herein, high-crystalline 3D core-shell hollow porous hexagonal tubular sulfur-doped carbon nitride (S-TCN) was synthesized through a simple and environmentally friendly supramolecular self-assembly strategy combined with a “salt-sealing” technique. This unique 3D structure facilitates the utilization of incident light, increases the active reaction sites, and improves interfacial mass transfer. The “salt-sealing” technique effectively enhances its crystallinity, while sulfur doping modification reduces the band gap and promotes separation and transfer of photogenerated carriers. Depend on the synergistic effect of morphology modulation, elemental doping, and high crystallinity, S-TCN exhibits significantly enhanced photoelectric conversion efficiency. It not only shows excellent performance for photocatalytic H2 production in pure water, but also rapidly degrades pollutants while maintaining H2 production activity in wastewater. The development of this dual-functional photocatalytic material holds important guiding significance for expanding the efficient application of polymer semiconductors.

First-principles study of the electron and phonon transport properties in monolayer boron monosulfide

Abstract Motivated by the excellent electronic properties of theoretical proposed monolayer boron monosulfides (BS) binary materials, which belong to a light-element member of the group IIIA chalcogenides family, we have investigated the electron and phonon transport properties of three monolayer phases of BS (α, β and γ) using first-principles and Boltzmann transport theory methods. The calculated electronic structures show that α- and β-BS are semiconductors with indirect bandgaps of 4.01 eV and 3.87 eV, respectively, whereas the γ-BS is a semiconductor with a direct bandgap of 2.97 eV. Additionally, due to their light carrier effective masses, superior high carrier mobilities are observed, thus bringing high Seebeck coefficients. We also find that due to the absence of imaginary phonon frequencies, the three monolayer phases of BS show dynamical stability. The phonon group velocity and relaxation time are also calculated to analyze the phonon thermal conductivity. We find that strong phonon scattering makes γ-BS monolayer possess extremely low phonon thermal conductivity (1.2 and 2.7 Wm−1K−1 along the x and y directions at 300 K, respectively), whereas α- and β-BS monolayers show a relatively high phonon thermal conductivity. Therefore, the highest predicted ZT value of 1.7 ( n -type) at 700 K is obtained for monolayer γ-BS along the x direction. However, α- and β-BS monolayers have extremely low ZT values. Our results reveal that the γ-BS monolayer has wider promising applications in high performance thermoelectric material than α- and β-BS monolayers.

Advancing the Commercialization of Perovskite‐Based Radiation Detectors for High‐Resolution Imaging

AbstractRadiation detectors play an indispensable role in medical diagnostics, industrial non‐destructive inspection and national security. Recently, halide perovskites are considered as the new generation of radiation active materials due to excellent optoelectronic properties such as adjustable bandgap, high absorption coefficient, high carrier mobility and low cost. The radiation detectors based on perovskite show high sensitivity and low detection limit, contributing to excellent spatial resolution for imaging. However, the commercialization of perovskite radiation detectors for high quality imaging still faces many challenges, including ion migration in perovskite, fermi level pinning and electrochemical reaction at the interface of perovskite/electrode, and difficulties of integration with readout circuit. All the issues hinder the further improvement of device performance. This review summarizes the material forms and the optimized growth methods of perovskite for radiation imaging detectors. Further, this work focuses on challenges and improvements of the interface between perovskites and electrodes. Meanwhile, this work outlines the technical routes used to realize array detectors for radiation imaging. The comprehensive review would guide the commercialization of perovskite radiation detectors for high‐quality imaging.

ZrS2/Ga2SSe heterojunction: A direct Z-scheme heterojunction with excellent photocatalytic performance across the entire pH range and high solar-to-hydrogen efficiency

Developing photocatalytic water splitting materials for hydrogen production is a crucial strategy for achieving sustainable energy utilization. This study proposes a ZrS2/Ga2SSe van der Waals heterojunction and conducts an in-depth analysis through first-principle calculations. The results show that the heterojunction possesses an indirect bandgap of 1.33 eV, which contributes to its superior optical performance. Its band structure and built-in electric field promote the Z-scheme electron transfer mechanism. High carrier mobility in the heterojunction improves photocatalytic efficiency. Strain engineering further enhances its electronic and optical properties, allowing water splitting across all pH levels within a biaxial strain range of −4% to +2%. Under a −6% compressive strain, there is a 63.06% enhancement in optical performance within the visible light spectrum, and the solar-to-hydrogen efficiency reached 10.93%. Gibbs free energy analysis indicates that the hydrogen evolution reaction, powered by photogenerated electrons, requires only 0.19 eV of energy. Therefore, the ZrS2/Ga2SSe heterojunction is identified as a promising visible-light-driven catalyst for water splitting.

Discovery of superconductivity and electron-phonon drag in the non-centrosymmetric Weyl semimetal LaRhGe3

We present an exploration of the effect of electron-phonon coupling and broken inversion symmetry on the electronic and thermal properties of the semimetal LaRhGe3. Our transport measurements reveal evidence for electron-hole compensation at low temperatures, resulting in a large magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on the order of 1021/cm3 with high carrier mobilities of 2000 cm2/Vs. When coupled to our theoretical demonstration of symmetry-protected almost movable Weyl nodal lines, we conclude that LaRhGe3 supports a Weyl semimetallic state. We discover superconductivity in this compound with a Tc of 0.39(1) K and Bc(0) of 2.2(1) mT, with evidence from specific heat and transverse-field muon spin relaxation. We find an exponential dependence in the normal state electrical resistivity below ~50 K, while Seebeck coefficient and thermal conductivity measurements each reveal a prominent peak at low temperatures, indicative of strong electron-phonon interactions. To this end, we examine the temperature-dependent Raman spectra of LaRhGe3 and find that the lifetime of the lowest energy A1 phonon is dominated by phonon-electron scattering instead of anharmonic decay. We conclude that LaRhGe3 has strong electron-phonon coupling in the normal state, while the superconductivity emerges from weak electron-phonon coupling. These results open up the investigation of electron-phonon interactions in the normal state of superconducting non-centrosymmetric Weyl semimetals.

Modification Strategies and Prospects for Enhancing the Stability of Black Phosphorus.

Black phosphorus is a two-dimensional layer material with promising applications due to its many excellent physicochemical properties, including high carrier mobility, ambipolar field effect and unusual in-plane anisotropy. Currently, BP has been widely used in biomedical engineering, photocatalysis, semiconductor devices, and energy storage electrode materials. However, the unique structure of BP makes it highly chemically active, leading to its easy oxidation and degradation in air, which limits its practical applications. Recently, researchers have proposed a number of initiatives that can address the environmental instability of BP, and the application of these physical and chemical passivation techniques can effectively enhance the environmental stability of BP, including four modification methods: covalent functionalization, non-covalent functionalization, surface coordination, physical encapsulation and edge passivation. This review highlights the mechanisms of the above modification techniques in addressing the severe instability of BP in different application scenarios, as well as the advantages and disadvantages of each method. This review can provide guidance for more researchers in studying the marvellous properties of BP and accelerate the practical application of BP in different fields.

Double Gold/Nitrogen Nanosecond-Laser-Doping of Gold-Coated Silicon Wafer Surfaces in Liquid Nitrogen

A novel double-impurity doping process for silicon (Si) surfaces was developed, utilizing nanosecond-laser melting of an 11 nm thick gold (Au) top film and a Si wafer substrate in a laser plasma-activated liquid nitrogen (LN) environment. Scanning electron microscopy revealed a fluence- and exposure-independent surface micro-spike topography, while energy-dispersive X-ray spectroscopy identified minor Au (~0.05 at. %) and major N (~1–2 at. %) dopants localized within a 0.5 μm thick surface layer and the slight surface post-oxidation of the micro-relief (oxygen (O), ~1.5–2.5 at. %). X-ray photoelectron spectroscopy was used to identify the bound surface (SiNx) and bulk doping chemical states of the introduced nitrogen (~10 at. %) and the metallic (<0.01 at. %) and cluster (<0.1 at. %) forms of the gold dopant, and it was used to evaluate their depth distributions, which were strongly affected by the competition between gold dopants due to their marginal local concentrations and the other more abundant dopants (N, O). In this study, 532 nm Raman microspectroscopy indicated a slight reduction in the crystalline order revealed in the second-order Si phonon band; the tensile stresses or nanoscale dimensions of the resolidified Si nano-crystallites envisioned by the main Si optical–phonon peak; a negligible a-Si abundance; and a low-wavenumber peak of the Si3N4 structure. In contrast, Fourier transform infrared (FT-IR) reflectance and transmittance studies exhibited only broad structureless absorption bands in the range of 600–5500 cm−1 related to dopant absorption and light trapping in the surface micro-relief. The room-temperature electrical characteristics of the laser double-doped Si layer—a high carrier mobility of 1050 cm2/Vs and background carrier sheet concentration of ~2 × 1010 cm−2 (bulk concentration ~1014–1015 cm−3)—are superior to previously reported parameters of similar nitrogen-implanted/annealed Si samples. This novel facile double-element laser-doping procedure paves the way to local maskless on-demand introductions of multiple intra-gap intermediate donor and acceptor bands in Si, providing related multi-wavelength IR photoconductivity for optoelectronic applications.

A Facile Electrochemical Strategy for Achieving a High-Conductivity Polypyrrole Derivative with Intrinsic Metallic Transport as a High-Performance Electrochromic Conducting Polymer Film.

Conjugated polymer electrochromic materials (PECMs) with tailored optical and electrical properties are applied in smart windows, electronic displays, and adaptive camouflage. The limitation in the electrical conductivity results in slow and monotonous color switching. We present a polypyrrole film incorporated with a toluene-p-sulfonic group (PPy-TSO-F), via a one-step electrodeposition technique. The PPy-TSO-F thin film (110 nm) achieves an impressive electrical conductivity of 1011 S cm-1, a high carrier mobility of 82 cm2 V-1 s-1, and intrinsic metallic electronic behavior. It demonstrates exceptionally reversible multicolor switching, transitioning from emerald green (-1.5 V), to bluish green (-1.4 V), bright yellow (-1.2 V), greenish yellow (-0.6 V), reddish brown (0.1 V), dark brown (0.3 V), and atrovirens (0.6 V). The fast charge transport and high carrier mobility render the film with an ultrafast electrochromic switching speed of 0.01 s/0.02 s. This research provides a new route to designing ultrafast multicolor switching PECMs with metallic charge transport.

Structural, electronic, and magnetic properties of binary zigzag antimonene-phosphorene nanoribbons and their mole fractions with different edge passivation: A DFT investigation

The study focuses on binary antimonene-phosphorene, a two-dimensional semiconductor material known for its high carrier mobility, suitable band gap, and strong environmental stability, making it appealing for electronics and spintronics applications. In this study, using density functional theory, we investigated the structural stability and electronic-magnetic properties of zigzag SbP nanoribbons, as well as single Sb and single P nanoribbons. Various edge passivation (H, F, Cl, O, S) are considered, along with different phosphorus mole fractions. The findings show that SbP structures with 25 % phosphorus mole fractions, as well as those passivated with various atoms, demonstrate strong conformational stability. SbP nanoribbons passivated with H, F, and Cl exhibit non-magnetic semiconductor behavior, while those passivated with O and S display magnetic metallic properties. Maximal magnetization is observed in SbP nanoribbons passivated with single S atoms, particularly magnetizing both Sb and P atoms at the edges. Additionally, SbP nanoribbons passivated with dual O atoms show negative differential resistivity and a complete spin filtering effect (100 %). The study also investigates the variation in magnetization across structures with different phosphorus mole fractions. Overall, the study demonstrates that adjusting phosphorus mole fractions and edge passivation can significantly modify the electronic and magnetic properties of SbP nanoribbons, making them suitable for spintronic nanodevices.

Comparative Analysis of Structural, Optical, and Electronic Properties of Nickel Oxide and Potassium‐Doped Nickel Oxide Nanocrystals

ABSTRACTMetal oxide semiconductors, known for their exceptional optical transparency, high carrier mobility, and stability, have found extensive use in emerging technologies such as optoelectronics and energy storage devices. Among all metal oxide semiconductors, nickel oxide (NiO) stands out as a highly favorable candidate due to its p‐type conductivity along with its substantial band gap (3.5–4 eV) for the broad range of applications, including gas sensors, high‐rate Lithium‐ion batteries, high‐performance supercapacitors, and photovoltaic devices. In light of these versatile applications, our current study presents a comprehensive comparative analysis of the structural and optoelectronic properties of NiO and potassium (K)‐doped NiO nanocrystals. The nanocrystals were synthesized using the co‐precipitation route and subsequently annealed at 500°C under ambient conditions. The effect of K doping on the structural and optoelectronic characteristics was systematically examined using various techniques, including x‐ray diffraction, UV–visible spectroscopy, Raman spectroscopy, and Hall effect measurements. To explore the structural characteristics, XRD measurements were performed, which confirm the FCC structure of nanocrystals. The optical property analysis suggested that the formation of the energy level can contribute to reduction of the band gap. A sharp peak at 397 cm−1 is associated with NiO bond in FTIR spectra which verifies the formation of nanocrystals. Moreover, the incorporation of K increases the intensity of the Raman peaks, which provides evidence for the higher degree of crystallinity in doped samples. These results of Raman scattering are in good agreement with XRD outcomes. In addition, the resistivity of NiO nanocrystals decreases monotonically with the increasing K concentration. The results of temperature‐dependent resistivity further demonstrate that electrons required more energy to jump from one polaron state to another in the case of x = 0.01 M and 0.03 M doped Ni0.5‐xKxO samples. The combination of a diminished band gap and enhanced conductivity makes these materials exceptionally promising for applications in optoelectronics and energy storage.

Demonstration of irradiation-resistant 4H-SiC based photoelectrochemical water splitting

4H silicon carbide (4H-SiC) has gained a great success in high-power electronics, owing to its advantages of wide bandgap, high breakdown electric field strength, high carrier mobility, and high thermal conductivity. Considering the high carrier mobility and high stability of 4H-SiC, 4H-SiC has great potential in the field of photoelectrochemical (PEC) water splitting. In this work, we demonstrate the irradiation-resistant PEC water splitting based on nanoporous 4H-SiC arrays. A new two-step anodizing approach is adopted to prepare 4H-SiC nanoporous arrays with different porosity, that is, a constant low-voltage etching followed by a pulsed high-voltage etching. The constant-voltage etching and pulsed-voltage etching are adopted to control the diameter of the nanopores and the depth of the nanoporous arrays, respectively. It is found that the nanoporous arrays with medium porosity has the highest PEC current, because of the enhanced light absorption and the optimized transportation of charge carriers along the walls of the nanoporous arrays. The performance of the PEC water splitting of the nanoporous arrays is stable after the electron irradiation with the dose of 800 and 1600 kGy, which indicates that 4H-SiC nanoporous arrays has great potential in the PEC water splitting under harsh environments.

Novel multi-layered MXene as laser desorption ionization mass spectrometry matrix for rapid detection of small biomolecules

Five two-dimensional multi-layered MXenes namely MO2C, Ti2C, V2C, Nb2C and Ta2C were synthesized by a one-step exfoliation process and evaluated as laser desorption ionization mass spectrometry (LDI-MS) matrices for fast detection of small biomolecules for the first time. Among them, Nb2C exhibited the best performance due to its high carrier mobility, strong photo-induced charge transfer resonance and good UV absorption ability. A simple, universal and efficient LDI-MS platform was established for small biomolecule analysis based on the Nb2C matrix. Key factors that affect LDI-MS efficacy were investigated and the established method demonstrated ultraclean MS background, high sensitivity with detection limits low to fmol level and good reproducibility. The Nb2C-based LDI-MS platform was successfully applied in the rapid determination of 13 amino acids (AAs) in human serum and 3 AAs, as potential biomarkers, were found to be significantly down-regulated in major depressive disorder patients. This work proved the feasibility of Nb2C MXene as an LDI-MS matrix and provided a promising and universal platform for the rapid detection of small molecules in biomedical research.

Enhanced electrical and mechanical properties of graphene/copper composite through reduced graphene oxide-assisted coating

Modifying the surface of metallic materials with graphene (Gr) holds significant potential for achieving high electrical conductivity in metal-based composites, leveraging the synergistic effect of the high carrier concentration in metals and the high carrier mobility of Gr. However, the strong van der Waals forces and large specific surface area of Gr sheets often lead to agglomeration in slurrys, adversely affecting the arrangement of Gr layers within the coating structure. In this study, we introduce reduced Gr oxide (rGO) into the Gr slurry to enhance the electrostatic stability and dispersion of Gr sheets through π-π interactions. By precisely controlling the composition of the coating, a compact, low-roughness coating was prepared on the surface of the copper (Cu) wire. The fabricated Gr/rGO/Cu composite wire exhibited a high conductivity of 104.2% IACS, with a tensile strength of 266.1 MPa and the elongation of 36.3%, respectively. This study demonstrates that the addition of rGO improves the dispersibility of Gr in the slurry, leading to a more compact and effective composite structure. The Gr/rGO/Cu composite wires exhibit superior electrical and mechanical properties, making them promising candidates for high-performance applications in electrical and electronic industries.

Emerging New-Generation Semiconductor Single Crystals of Metal Halide Perovskites for Radiation Detection

Radiation detection uses semiconductor materials to convert high-energy photons into charge (direct detection) or low-energy photons (indirect detection), and it has a wide range of applications in nuclear physics, medical imaging, astronomical detection, homeland security, and other fields. Metal halide perovskites have the advantages of high frequency number, high carrier mobility, high defect tolerance, low defect density, adjustable band gap, and fast light response, and they have wide application prospects in the field of radiation detection. However, the research is still in its infancy stage, and it is far from meeting the requirements of industrial application. This paper focuses on the advantages of metal halide perovskite single-crystal materials in both semiconductors-based direct conversion detection and scintillator-based indirect detection as well as the latest progress in this promising field. This paper not only introduces the latest application of lead halide perovskite monocrystalline materials in high-energy electromagnetic radiation detection (X-ray and γ-rays), but it also introduces the latest development of α-particle/β-particle/neutron detection. Finally, this paper points out the challenges and future prospects of metal halide perovskite single-crystal materials in radiation detection.

Key Sputtering Parameters for Precursor In2O3 Films to Achieve High Carrier Mobility.

Owing to their extremely high carrier mobility (μ) of >100 cm2/(V s) and suitable low carrier concentrations, transparent conducting films of solid-phase crystallized H-doped In2O3 (spc-IO:H) exhibit high conductivity with high optical transparency over a broad frequency range. These properties can be attributed to solid-phase crystallization of the amorphous precursor film. Therefore, the development of high-quality spc-IO:H films requires the deposition conditions of the precursor films to be optimized. This study systematically investigates the effects of three key sputtering parameters, namely, water vapor partial pressure (PH2O), radio frequency magnetron sputtering power (PRF), and flow ratio of O2 to total sputter gas (fO2) on the crystallographic texture evolution of spc-IO:H films during solid-phase crystallization. In addition, the carrier transport in the resulting films is examined. PH2O, PRF, and fO2 are found to be indispensable for producing high-mobility (>100 cm2/(V s)) spc-IO:H films. Furthermore, it is found that introducing a small amount of PH2O during deposition, a lower PRF, and a suitable fO2 facilitates the formation of precursor films having a lower crystallite density. Moreover, after annealing at a temperature of 200 °C, the IO:H precursor films with a lower crystallite density are found to have larger crystal grains. However, the μ values of the postannealed IO:H films are mainly correlated with the stoichiometric deviation.

Fractional quantum Hall phases in high-mobility n-type molybdenum disulfide transistors

Transistors based on semiconducting transition metal dichalcogenides can, in theory, offer high carrier mobilities, strong spin–orbit coupling and inherently strong electronic interactions at the quantum ground states. This makes them well suited for use in nanoelectronics at low temperatures. However, creating robust ohmic contacts to transition metal dichalcogenide layers at cryogenic temperatures is difficult. As a result, it is not possible to reach the quantum limit at which the Fermi level is close to the band edge and thus probe electron correlations in the fractionally filled Landau-level regime. Here we show that ohmic contacts to n-type molybdenum disulfide can be created over a temperature range from millikelvins to 300 K using a window-contacted technique. We observe field-effect mobilities of over 100,000 cm2 V−1 s−1 and quantum mobilities of over 3,000 cm2 V−1 s−1 in the conduction band at low temperatures. We also report evidence for fractional quantum Hall states at filling fractions of 4/5 and 2/5 in the lowest Landau levels of bilayer molybdenum disulfide.