Electrical Transport Characteristics Research Articles

Tunable Polarity in WSe2/TiS2 Van Der Waals Heterostructure

Two-dimensional (2D) transition metal dichalcogenides (TMDs) formed layered van der Waals (vdW) crystals have emerged as promising candidates for varieties of potential applications, such as gas sensors, photodetectors, light-emitting diodes, Schottky diodes and memories, due to their unique physical features. However, since the existence of the metal-induced gap states (MIGS) at metal-semiconductor interfaces, it is severely difficult to adjust their electrical properties. It was demonstrated in previous researches that various metal contacts on TMDs semiconductor exhibit regular Schottky barrier height by Fermi-level pinning effect.In this study, we suggest the van der Waals material contact between TiS2 semimetal and WSe2 semiconductor for leading van der Waals gap at their interface. Through this approach, the TiS2/WSe2 2D heterojunction can efficiently address the MIGS. Interestingly, the TiS2/WSe2 heterojunction exhibits a novel electrical transport characteristics such as distinct ambipolar and rectifying behaviors by tuning drain voltage polarity. Firstly, under reverse bias (V ds < 0), TiS2/WSe2 heterojunction operates efficiently and allows transport of the carriers at both polarities of the gate voltage (V bg < 0 and V bg > 0), namely ambipolar behavior. Secondly, under the forward bias (V ds > 0), TiS2/WSe2 heterojunction does not allow transport of the electrons at positive gate voltage (V bg > 0), but allow transport of the holes at negative gate voltage (V bg < 0), namely p-type behavior. To understand the carrier transport mechanism of these results, ultra-violet photoelectron spectroscopy (UPS) measurements were also carried out on the WSe2 and TiS2 flakes. It is noted that the TiS2/WSe2 junction plays a crucial role in determining a novel electronic property of this device. Figure 1

Centimeter-Scale MoS2 Thin Films As a Temperature Sensor

Backgrounds/Introduction Transition-metal dichalcogenides (TMDs) is an atomically-thin semiconducting material family, exhibiting unique physical and multi-functional properties. Despite the great promises in flexible electronics, the practical adoption of TMDs in a wider variety of far-reaching application domains, including high-temperature applications such as automobiles and aircrafts, still requires TMDs to be prepared at a larger scale and tailor-researched to the needs of a specific application. In this work, molybdenum disulfide (MoS2), one of the most widely studied TMD materials, is synthesized at a centimeter-scale by sulfurizing the transition metal seed layer (Mo) in a CVD (chemical vapor deposition) reactor, and comprehensively characterized to explore MoS2’s potential as the next-generation temperature sensor. Key Results: Fig. 1 depicts both the schematic drawing (1a) and the transmission electron microscope (TEM) image (1b) of few-layer MoS2 thin films grown on a SiO2/Si substrate by the CVD process described in our earlier work [1]. As seen in the figure, 2D MoS2 layers were successfully grown in a planar direction with their basal planes parallel to the growth substrates. The horizontal growth of few-layer MoS2 thin films (thicknesses of less than 5 nm) was achieved by precisely controlling the thickness of the metal seed layer (Mo).We first investigated the Raman characteristics of our centimeter-scale (2cm x 2cm), CVD-grown MoS2 thin films at varying temperatures (from 26°C to 206°C) in Fig. 2. It is clearly seen that both E2g (out-of-plane vibration modes at ~ 383 cm-1) and A1g (in-plane vibration modes at ~ 408 cm-1) characteristic peaks appeared in the temperature-dependent Raman measurement. Since these peak positions are known to be strongly dependent on materials or external parameters (e.g., thickness, mechanical strain, charge transfer), observing any notable change in the peak position at varying conditions can lead to discovery of MoS2’s novel functionality. The overall trend of red shift (i.e., decrease of Raman shift) with an increase in temperature observed in Fig. 3 is in good agreement with what has been already reported for an exfoliated single-layer MoS2 flake [2]. This has been attributed to either charge transfer from the substrate (doping effect) or compressive strain resulted from thermal expansion coefficient mismatch between MoS2 and the substrate.In order to further elucidate the physical mechanism while examining the potential of MoS2 to become a temperature sensor of the RTD (resistance temperature detector) type, we carefully measured the conductivity vs. temperature characteristics by using the temperature controller-attached probe station (Figs. 4 and 5). Firstly, a clear trend of increase in electrical conductivity with temperature indicates the semiconducting nature of our MoS2 thin films (Fig. 4). More importantly, Fig. 5 suggests that electronic transport in the temperature range of room temperature to about 300°C follows an Arrhenius behavior, implying a variable-range hopping mechanism [3]. Table 1 summarizes the temperature coefficient (cm-1/°C, measured from Raman) and the activation energy (eV, measured from the Arrhenius plot). Significance: Previously, researchers have studied the temperature dependence of electrical conductivity for exfoliated MoS2 flakes (either undoped [4] or doped [5]). These methods may not be best suited for temperature sensing applications because of the small areal size and lack of tight control on the thickness. This work significantly advances the field by demonstrating the temperature-induced modulation of spectroscopic and electrical transport characteristics of a relatively large-area MoS2 thin film.

Atomistic Modeling of the Electrical Conductivity of Single‐Walled Carbon Nanotube Junctions

Carbon nanotubes (CNTs) have many interesting properties that make them a focus of research in a wide range of technological applications. In CNT films, the bottleneck in charge transport is typically attributed to higher resistance at CNT junctions, leading to electrical transport characteristics that are quite different from individual CNTs. Previous simulations confirm this; however, a systematic study of transport across junctions is still lacking in the literature. Herein, density functional tight binding (DFTB) theory combined with the nonequilibrium Green's functions (NEGF) method is used to systematically calculate current across a range of CNT junctions. A random sampling approach is used to sample an extensive library of junction structures. The results demonstrate that the conductivity of CNT contacts depends on the overlap area between nanotubes and exponentially on the distances between the carbon atoms of the interacting CNTs. Two models based solely on the atomic positions of carbon atoms within the nanotubes are developed and evaluated: a simple equation using only the smallest C–C separation and a more sophisticated model using the positions of all C atoms. These junction current models can be used to predict transport in larger‐scale simulations where the CNT fabric structure is known.

The Effectiveness of Ga Percent on the Electrical Characteristics of Al/CuIn1-xGaxSe2/ITO Schottky Junctions

The electrodeposition method has been employed to deposit our quaternary semiconductor thin films CuIn1-xGaxSe2 (CIGS) which is deposited on Indium Tin Oxide (ITO) substrates with different Gallium ratios (x=0, 0.2, 0.4, 0.6, 0.8 and 1). The structural and optical characteristics variation of the films with altering Ga percent has been studied. The impact of changing the Ga/(In+Ga) atomic ratio on the electrical transport characteristics of electrodeposited CIGS thin films has been investigated using I-V and C-V measurements. All junctions have revealed the Schottky behavior. The energy gap of the studied compositions has increased with increasing Ga content. This lowered the values of charge mobility in the investigated films. Besides, the optimum Ga/(In+Ga) atomic proportion in the view of the obtained results is achieved by adding Ga with 20 %. Also, this finding approves the validation of our proposed criterion in expecting the most efficient photovoltaic junctions. The obtained results could improve our current knowledge of the quaternary photovoltaic solar cells.

Exciton Transfer at Heterointerfaces of MoS2 Monolayers and Fluorescent Molecular Aggregates.

Integration of distinct materials to form heterostructures enables the proposal of new functional devices based on emergent physical phenomena beyond the properties of the constituent materials. The optical responses and electrical transport characteristics of heterostructures depend on the charge and exciton transfer (CT and ET) at the interfaces, determined by the interfacial energy level alignment. In this work, heterostructures consisting of aggregates of fluorescent molecules (DY1) and 2D semiconductor MoS2 monolayers are fabricated. Photoluminescence spectra of DY1/MoS2 show quenching of the DY1 emission and enhancement of the MoS2 emission, indicating a strong electronic interaction between these two materials. Nanoscopic mappings of the light‐induced contact potential difference changes rule out the CT process at the interface. Using femtosecond transient absorption spectroscopy, the rapid interfacial ET process from DY1 aggregates to MoS2 and a fourfold extension of the exciton lifetime in MoS2 are elucidated. These results suggest that the integration of 2D inorganic semiconductors with fluorescent molecules can provide versatile approaches to engineer the physical characteristics of materials for both fundamental studies and novel optoelectronic device applications.

Charge transport in doped conjugated polymers for organic thermoelectrics

Research on conjugated polymers for thermoelectric applications has made tremendous progress in recent years, which is accompanied by surging interest in molecular doping as a means to achieve the high electrical conductivities that are required. A detailed understanding of the complex relationship between the doping process, the structural as well as energetic properties of the polymer films, and the resulting thermoelectric behavior is slowly emerging. This review summarizes recent developments and strategies that permit enhancing the electrical conductivity of p- and n-type conjugated polymers via molecular doping. The impact of the chemical design of both the polymer and the dopant, the processing conditions, and the resulting nanostructure on the doping efficiency and stability of the doped state are discussed. Attention is paid to the interdependence of the electrical and thermal transport characteristics of semiconductor host-dopant systems and the Seebeck coefficient. Strategies that permit to improve the thermoelectric performance, such as an uniaxial alignment of the polymer backbone in both bulk and thin film geometries, manipulation of the dielectric constant of the polymer, and the variation of the dopant size, are explored. A combination of theory and experiment is predicted to yield new chemical design principles and processing schemes that will ultimately give rise to the next generation of organic thermoelectric materials.

Influence of magnetron sputtering process parameters on low-temperature electrical transport characteristics of zirconium oxynitride thin films

In order to determine the influence of process parameters including nitrogen and oxygen flow rate on the structure and electrical transport characteristics of zirconium oxynitride(ZrOxNy) thin films, the ZrOxNy films were prepared on sapphire substrates by RF reactive magnetron sputtering deposition technology. The crystal orientation and morphology of ZrOxNy films prepared at different nitrogen and oxygen flow rate were characterized by XRD and SEM, respectively. The electric transport behavior of ZrOxNy films at 300K to 3K was measured by PPMS. The results show that the insulativity of ZrN films is enhanced with the increase of nitrogen flow rate in sputtering atmosphere. With the increase of oxygen flow rate in sputtering atmosphere, the insulativity of ZrOxNy film is enhanced.

Spectra dependent photonic structure design for energy harvesting by indoor photovoltaic devices

In this work, we report spectra-dependent energy harvesting by optimizing the photon management of an indoor photovoltaic device while taking into consideration the degradation of electrical transport characteristics caused by the nano-photonic structures. For the test case of a CdTe-based photovoltaic device, it has been shown that although the incorporation of dielectric-filled nanoholes in the absorber layer can enhance light absorption by about 40%, the optical-to-electrical conversion efficiency of the device is significantly diminished because of the degradation of the electrical transport characteristics. Instead, the best performance metrics are obtained when the nanostructures are incorporated in the window layer of the device alone. A finite difference time domain based numerical analysis, coupled with Poisson’s equation and continuity equation, shows that by controlling the areal density of the optimized structure in direct correlation with spectral characteristics of the illuminating light source, it is possible to maximize the overall power conversion efficiency of the indoor photovoltaic device. In the case of commercial white light-emitting diodes (LEDs), large arealdensities of holes are found to be more conducive for harvesting energy from cool-white LEDs, whereas smaller areal densities of holes provide better performances for illumination under warm-glow white LEDs.

Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa.

High-pressure structural, vibrational, and electrical transport properties of CrCl3 were investigated by means of Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy under different hydrostatic environments using the diamond anvil cell in conjunction with the first-principles theoretical calculations up to 50.0 GPa. The isostructural phase transition of CrCl3 occurred at 9.9 GPa under nonhydrostatic conditions. As pressure was increased up to 29.8 GPa, CrCl3 underwent an electronic topological transition accompanied by a metallization transformation due to the discontinuities in the Raman scattering and electrical conductivity, which is possibly belonging to a typical first-order metallization phase transition as deduced from first-principles theoretical calculations. As for the hydrostatic condition, a ∼2.0 GPa pressure delay in the occurrence of two corresponding transformations of CrCl3 was observed owing to the different deviatoric stress. Upon decompression, we found that the phase transformation from the metal to semiconductor in CrCl3 is of good reversibility, and the obvious pressure hysteresis effect is observed under different hydrostatic environments. All of the obtained results on the structural, vibrational, and electrical transport characterizations of CrCl3 under high pressure can provide a new insight into the high-pressure behaviors of representative chromium trihalides CrX3 (X = Br and I) under different hydrostatic environments.

High electrical transport performance of C12A7: e– ceramics electrides on Cu‐doping

Abstract(Ca1‐xCux) 12A7: e– bulks (0 ≤ x ≤ 0.05) with electrical performance were fabricated by the in‐situ aluminothermic synthesis. The results showed that all the electron concentrations of (Ca1‐xCux) 12A7: e– reached the theoretical value of about 2.28 × 1021 cm–3. In (Ca0.96Cu0.04) 12A7: e–, the electron mobility at room temperature increased from 3.81 to 5.19 cm2 V–1 S–1 and the conductivity increased from 415 to 1405 S cm–1. It indicated that Cu‐doping effectively improved electrical properties. The photoexcitation property also changed positively. The energy required for electrons to transition from cage conduction band to frame conduction band showed a decreasing trend, from 2.23 to 1.48 eV. The first‐principle calculation showed an upward shift in the Fermi energy level position of C12A7: e–. In addition, Cu atoms provided more density of states near the Fermi energy level. The number of empty orbitals near the Fermi surface of (Ca1‐xCux) 12A7: e– that can receive excited electrons increased. It provided a theoretical basis for preparing (Ca1‐xCux) 12A7: e– with high electrical transport characteristics.

Study of electronic structure, electrical characteristics and transport properties of heteroatoms (N, O &amp; S) based Anthracene molecular Nanowires-A DFT Study

For designing the electronic devices using molecular wires, it is important to understand the electronic properties at the molecular level. In this paper, the simulation methodology for analyzing the electrical conductivity of anthracene conjugated molecule sandwich between Au atoms via linker Sulfur atom, is proposed. This theoretical analysis is carried out for different applied electric field ranges from 0 to 0.26 VÅ-1 to metal electrode Au atom using density functional theory (DFT). The effect of external applied electric field towards the structural variation of metal attached anthracene molecule [WH] is well explored and compared the results with that of hetero atoms [N, S, and O] substituted heterocyclic systems [HAA, HTA and HOA]. Further, the ability of electron flow through these systems were explored from the analysis frontier molecular orbitals and density of states (DOS). The bonding nature of the studied molecules were well described from the QTAIM analysis and finally the reactive sites for electrophilic and nucleophilic attack was identified from the simulation of molecular electrostatic potential surface. Non-covalent interaction (NCI-RDG) analysis is addressed to characterize the interactions in heteroatom substituted anthracene based molecular nanowires. In our overall study, the outcomes are exposing that the significates feature and importance of electrical conductivity nature and transport characteristic of hetero-atoms (N, S, O) substituted anthracene based molecular nanowires.

Magnetic field induced alignment of macroradical epoxy for enhanced electrical properties.

Improving the electrical performance of macroradical epoxy thermosets to surpass the semiconductor threshold requires a comprehensive understanding of the electrical charge transport mechanisms and characteristics. In this study, we investigate the electrical properties of a non-conjugated radical thermoset in a rigid, three-dimensional (3D) motif cured under an external magnetic field. The outcomes of the four-angle analysis of the synchrotron IRM beamline provide for the first time quantitative insights into the molecular orientation at the atomic-scale level. These insights, in turn, were utilized to apply Quantum Computational modeling theories and Monte Carlo simulation to study the effect of the magnetic field-induced molecular alignment on tuning electrical charge transport characteristics. The results explored the impact of radical density on forming percolation networks, showing a robust protocol for designing polymers with high electrical/thermal conductivity.

Growth behaviors of epitaxial barium molybdate (BaMoO&lt;sub&gt;3&lt;/sub&gt;, BaMoO&lt;sub&gt;4&lt;/sub&gt;) film

Transition metal oxides have been a research hotspot for basic scientific research and frontier applications. Owing to the presence of d&lt;italic/&gt; electrons and strong electron correlation, a wealth of physical phenomena emerges in the transition metal oxide family. In particular, extremely fruitful research progress is achieved in a 3d orbital elemental system. In comparison, the 4d transition metal oxides need more attention. Molybdate has excellent optical and electrical properties. Among &lt;i&gt;A&lt;/i&gt;MoO&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;A&lt;/i&gt; = Ca, Sr, Ba), only BaMoO&lt;sub&gt;3&lt;/sub&gt; has not been reported for epitaxial films to date. In this work, high-quality epitaxial films of BaMoO&lt;sub&gt;3&lt;/sub&gt; and BaMoO&lt;sub&gt;4&lt;/sub&gt; are prepared by using the pulsed laser deposition. We conduct the oxygen partial pressure modulation experiments and the results show that the growth of BaMoO&lt;sub&gt;3&lt;/sub&gt; is sensitive to oxygen partial pressure. Also, BaMoO&lt;sub&gt;3&lt;/sub&gt; has a geometrically similar lattice structure to BaMoO&lt;sub&gt;4&lt;/sub&gt;, and there exists epitaxial competition between BaMoO&lt;sub&gt;3&lt;/sub&gt; and BaMoO&lt;sub&gt;4&lt;/sub&gt;. These two points make the preparation of epitaxial BaMoO&lt;sub&gt;3&lt;/sub&gt; films more challenging. The key to the preparation of epitaxial BaMoO&lt;sub&gt;3&lt;/sub&gt; thin films is the reduced laser target material, high vacuum environment, and ultra-low oxygen partial pressure. The epitaxy competition can be avoided by using the SrTiO&lt;sub&gt;3&lt;/sub&gt; (111) substrate. We conduct oxygen partial pressure modulation experiments on a narrow scale and reveal a self-assembled superlattice of epitaxial BaMoO&lt;sub&gt;3&lt;/sub&gt; film on a SrTiO&lt;sub&gt;3&lt;/sub&gt;(111) substrate. Both the satellite peaks in the XRD pattern and the HRTEM results indicate the superlattice period of about 7.04 Å. The oxygen partial pressure is the only parameter that regulates this phenomenon, so we presume that the essence of the self-assembled superlattice is periodic oxygen-induced lattice defects. Finally, electrical transport characterization experiments are conducted on representative BaMoO&lt;sub&gt;3&lt;/sub&gt; films. The &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}$\rho \text{-} T$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220736_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220736_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; curve measurements and fitting results show that the epitaxial BaMoO&lt;sub&gt;3&lt;/sub&gt; films on SrTiO&lt;sub&gt;3&lt;/sub&gt;(001) substrates have better conductivities. The electrical transport properties of BaMoO&lt;sub&gt;3&lt;/sub&gt; films grown on SrTiO&lt;sub&gt;3&lt;/sub&gt;(111) substrates are dominated by electron-phonon scattering, and BaMoO&lt;sub&gt;3&lt;/sub&gt; films grown on SrTiO&lt;sub&gt;3&lt;/sub&gt;(001) substrate have stronger electron-electron scattering interactions. The resistivity of the self-assembled superlattice BaMoO&lt;sub&gt;3&lt;/sub&gt; films is relatively high and electron-electron scattering plays an important role in determining the electrical transport property.

Lateral electrical transport and field-effect characteristics of sputtered p-type chalcogenide thin films

Investigating lateral electrical transport in p-type thin film chalcogenides is important to evaluate their potential for field-effect transistors (FETs) and phase-change memory applications. For instance, p-type FETs with materials sputtered at low temperature (≤ 250 °C) could play a role in flexible electronics or back-end-of-line silicon-compatible processes. Here, we explore lateral transport in chalcogenide films (Sb2Te3, Ge2Sb2Te5, and Ge4Sb6Te7) and multilayers, with Hall measurements (in ≤ 50 nm thin films) and with p-type transistors (in ≤ 5 nm ultrathin films). The highest Hall mobilities are measured for Sb2Te3/GeTe superlattices (∼18 cm2 V−1 s−1 at room temperature), over 2–3× higher than the other films. In ultrathin p-type FETs with Ge2Sb2Te5, we achieve field-effect mobility up to ∼5.5 cm2 V−1 s−1 with on/off current ratio of ∼104, the highest for Ge2Sb2Te5 transistors to date. We also explore process optimizations (e.g., the AlOx capping layer, type of developer for lithography) and uncover their tradeoffs toward the realization of p-type transistors with acceptable mobility and on/off current ratio. Our study provides essential insights into the optimization of electronic devices based on p-type chalcogenides.

Multiple mechanisms of the low temperature photoresponse in niobium diselenide

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide with novel quantum phases at low temperatures (T) such as superconductivity and charge density wave order. While its electronic correlations and the interaction between electrons and other collective modes have been explored extensively, a detailed study of the transport behavior of photo-excited charge carriers still remains elusive. Here, we report a systematic investigation of the photoresponse generated in homogenous NbSe2 nano-flakes near the superconducting critical temperature (Tc). By combining scanning photocurrent microscopy and classic photoconductivity measurements, three distinctive mechanisms of the photoresponse are established, including the band bending at the NbSe2–metal junction, the perturbation of the superconducting state, and the photo-bolometric effect. Among them, the photo-induced phase transition from the superconducting to normal state results in an extremely large photocurrent, which is tunable by the bias voltage and is consistent with the observation via the electrical transport characterization. The photoresponsivity of our device reaches 42.3 A/W, and the response time is less than 2 μs at T = 3.8 K for an excitation in the visible wavelength, whose performance could be further improved by optimizing the device design and the experimental condition. Our result sheds light on ultrasensitive broadband photodetection with atomically thin NbSe2 and points to a potential means of probing the correlated electronic phases by exploring light–matter interactions.

The self-powered artificial synapse mechanotactile sensing system by integrating triboelectric plasma and gas-ionic-gated graphene transistor

The emulation of biological nerves to develop artificial synapse tactile sensing system has great application potentials in the fields of Internet of Things and artificial intelligence. Novel sensing strategies to achieve low power consumption, low cost, low complexity and high efficiency still face challenges. Here, a self-powered tactile sensing system has been developed by integrating a triboelectric plasma and a gas-ions-gated (GIG) graphene transistor, in which the GIG transistor is served as the artificial synapse, and the triboelectric plasma is served as both a tactile sensor and the driving signals of the GIG transistor. The N2+ ions in the triboelectric plasma are directly adsorbed on the graphene surface, acting as a floating gate of the GIG transistor to regulate its electrical transport characteristics. The adsorption density of N2+ ions reach up to 3.96 × 1012 cm−2 with a measured desorption energy of 196 meV. The theoretical simulation shows that the N2+ ion is adsorbed at the site of carbon vacancy on the graphene surface. By regulating the number, frequency and polarization of the discharge pulse, various synaptic behaviors are achieved, such as short-term depression, long-term depression, long-term potentiation, paired-pulse facilitation, etc. Also, the neural functions of learning and temporal decoding have been demonstrated in experiments. By combining triboelectric plasma and GIG transistor, a facile experimental scheme for a self-powered, integrated, and simple structured intelligent tactile sensing system has been proposed, which is highly expected to promote the development of intelligent sensing fields in the future.

A time-shared switching scheme designed for multi-probe scanning tunneling microscope.

We report the designof a time-shared switching scheme, aiming to realize the manipulation and working modes (imaging mode and transport measurement mode) switching between multiple scanning tunneling microscope (STM) probes one by one with a shared STM control system (STM CS) and an electrical transport characterization system. This scheme comprises three types of switch units, switchable preamplifiers (SWPAs), high voltage amplifiers, and a main control unit. Together with the home-made software kit providing the graphical user interface, this scheme achieves a seamless switching process between different STM probes. Compared with the conventional scheme using multiple independent STM CSs, this scheme possesses more compatibility, flexibility, and expansibility for lower cost. The overall architecture and technique issues are discussed in detail. The performances of the system are demonstrated, including the millimeter scale moving range and atomic scale resolution of a single STM probe, safely approached multiple STM probes beyond the resolution of the optical microscope (1.1 µm), qualified STM imaging, and accurate electrical transport characterization. The combinational technique of imaging and transport characterization is also shown, which is supported by SWPA switches with ultra-high open circuit resistance (909TΩ). These successful experiments prove the effectiveness and the usefulness of the scheme. In addition, the scheme can be easily upgraded with more different functions and numbers of probe arrays, thus opening a new way to build an extremely integrated and high throughput characterization platform.

The potential barrier-dependent carrier transport mechanism in n-SnO2/p-Si heterojunctions

The metal oxide semiconductor-based p-n heterojunctions have captured intense attention in electronic and optoelectronic industry thanks to their simple and low-cost production and superior performance. Among these metal oxide semiconductors, ZnO, SnO2 and TiO2 have a broad usage as main component for the fabrication of heterojunction-based electronic devices, such as diodes, photodiodes, photodetectors, sensors and solar cells. However, the investigations towards the in-depth understanding of transport mechanism of n-SnO2/p-Si heterojunction are scarce. Herein, electrical transport characteristics of n-SnO2/p-Si heterojunction diode fabricated using a hydrothermal method are investigated. The device exhibits an excellent rectifying behavior quantified by a rectification ratio of 4754 ± 50 and a turn-on voltage at around 3.89 ± 0.05 V. Based on the characteristic measurements, the values of built-in potential, valence and conduction band offsets are estimated to be 0.65 ± 0.03 V, 3.24 eV and 0.48 eV, respectively. Ultimately, the energy-band alignment of the device is elaborated to explain the basic understanding of its working principle. This study provides a guidance to interpret the carrier transport mechanism within the device.

Transient performance analysis of graphene FET gated via ionic solid by numerical simulations based on tight-binding method and Nernst–Planck–Poisson equations

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO2, has been replaced by solid electrolytes, such as LiP3O4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO2-gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li+ ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability.

Pressure-induced metallic phase transition in gallium arsenide up to 24.3 GPa under hydrostatic conditions

A series of experiments of structural, vibrational and electrical transport characterization of gallium arsenide (GaAs) have been performed up to 24.3 GPa under hydrostatic conditions in a diamond anvil cell (DAC) in conjunction with in situ Raman scattering spectroscopy, electrical conductivity measurements, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Upon compression, a phase transition from the zinc-blende (zb) to the orthorhombic (Cmcm) structure of GaAs was observed at 12.2 GPa through the discontinuous variations of the Raman shifts, Raman full-width at half-maximum values and electrical conductivity. Furthermore, the results of variable temperature electrical conductivity experiments confirmed that the high-pressure phase (Cmcm) exhibited one obvious metallic behavior. Upon decompression, the Raman scattering results of the recovered sample under ambient conditions indicated that the phase transition was reversible under hydrostatic conditions. The reversibility of the phase transition was further verified by HRTEM and AFM images for the recovered sample.