Semiconductor Graphene Research Articles

Nonzero Wavevector Excitation of Graphene by Localized Surface Plasmons.

Electrochemical surface-enhanced Raman scatteringmeasurements of single layer graphene provide unique information on resonant excitation induced by localized surface plasmons under controlled electron or hole doping. The highly confined electromagnetic field from the LSPs of the Au nanodimer structures prepared on defect-free graphene can generate holes and electrons of the electrochemical potentials beyond the limit of far-field light illumination. The electrochemical in situ SERS spectra prove nonzero wavevector excitation through the observation of normally forbidden Raman bands in graphene. The present findings point to a novel approach to breaking the limit of optoelectronic interactions and photochemical reactions of graphene and other semiconductors.

Photoexcitation triggering via semiconductor Graphene Quantum Dots by photochemical doping with Curcumin versus perio-pathogens mixed biofilms

Recently, antimicrobial photodynamic therapy (aPDT) as an alternative treatment modality has been used adjunctively in the treatment of periodontitis and peri-implantitis. Photosensitizing agents in the form of nanoparticles have been designed for improving the efficiency of aPTD. Graphene quantum dots are a special type of nanocrystals that can promote aPDT when coupled with curcumin (Cur). The main objective of the present study was to investigate the effects of photoexcited GQD-Cur on the metabolic activity of perio-pathogen mixed biofilms. GQD-Cur was synthesized and characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible spectrometry (UV-Vis), and X-ray diffraction (XRD). The cell cytotoxicity effect of GQD-Cur was evaluated on primary human gingival fibroblast (HuGu) cells. Perio-pathogen mixed biofilms including Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia photosensitized with GQD doped with Cur were irradiated with a blue LED at a wavelength of 435 ± 20 nm for 1 min, and then bacterial viability measurements were performed. The antimicrobial susceptibility profile, biofilm formation ability, amount of reactive oxygen species (ROS) released, and variations of gene expressions involved in biofilm formation were assessed. The SEM, DLS, FTIR, UV-Vis spectrometry, and XRD pattern confirmed that GQD-Cur was synthesized successfully. According to the results, GQD-Cur exhibited no cytotoxicity against HuGu cells. Photoexcited GQD-Cur resulted in a significant reduction in cell viability (93%) and biofilm formation capacity (76%) of peri-pathogens compared to the control group (P < 0.05). According to the results, a significant concentration-dependent increase in the ROS generation was observed in perio-pathogens mixed cells treated with different doses of GQD-Cur-aPDT. Moreover, rcpA, fimA, and inpA gene expression profiles were downregulated by 8.1-, 9.6-, and 11.8-folds, respectively. Based on the results, photoexcited GQD-Cur have a high potency of perio-pathogens suppression in planktonic and biofilm forms and downregulation of the biofilm genes expression pattern was exploited as a nanoscale-based platform for periodontitis.

Atom/molecular nanoarchitectonics for devices and related applications

Abstract Fusion of nanotechnology with the other science disciplines including organic chemistry, supramolecular chemistry, and biotechnology creates a new conceptual paradigm, nanoarchitectonics. In this review article, we focus on recent contribution of the nanoarchitectonics concept on device fabrication. In these approaches, various materials such as organic semiconductor crystals, carbon nanotubes, graphene, and nanosheets are nanoarchitected by self-assembled monolayer technique, meniscus-driven crystallization, photochemical layer-by-layer process, ice resist lithography, vortex Langmuir-Blodgett method to various devices including atomic switch, artificial synapses, decision-making device, nonvolatile memory, multi-valued logic circuits, organic field-effect transistors, conductive cellulose nanopapers, organic photovoltaics, fuel cells, biocompatible batteries, and microbial biophotovoltaic cells.

Highly Efficient and Broadband Hybrid Photodetector Based on 2-D Layered Graphene/CTS Quantum Dots

This paper reports the fabrication of a broadband near-infrared response (vis-NIR) photodetector (PD) using Cu2SnS3 (CTS) quantum dots (QDs) as photoactive semiconductor material and graphene as a carrier transport medium. The QDs of earth abundant, nontoxic, and inexpensive CTS have been synthesized by solvothermal method, and the chemical vapor deposition (CVD) technique is used to synthesize few layers and monolayers of graphene. The fabricated CTS QDs/graphene/SiO2/Si PD demonstrated high values of responsivity (~110.089 A/W), detectivity ( $\sim 1.25 \times 10^{{12}}\,\,\text {cm} \cdot \text {Hz}^{\text {1/2}} \cdot \text {W}^{-{1}}$ ), and quantum efficiency (~160.9) for broadband (vis-NIR) region due to high absorption coefficient of CTS QDs and very high mobility (~200 000 cm2/V–s) of graphene. The time-response analysis of PD was also performed under vis-NIR and ON and OFF time were found to be 10.2 and 11.34 s.

Surface Plasmon Polaritons in a Graphene–Semiconductor–Graphene Thin Film

Dispersion properties of surface plasmon polaritons in a semiconductor film with graphene plates in the far-IR range and the possibility of controlling propagation modes due to the change in the chemical potential on one or both plates have been investigated. Dispersion relations for the TE- and TM-polarized waves have been obtained and analyzed, and distributions of the wave field and energy fluxes over the structure have been constructed. Spectral ranges where the surface-wave group velocity is negative are found.

Interview

Guoping Guo Professor Guoping Guo from the Key Laboratory of Quantum Information at the University of Science and Technology of China, talks to Electronics Letters about the paper ‘Modelling and Kink Correction of 0.18 µm Bulk CMOS at Liquid Helium Temperature‘, page 780. I am currently studying solid state quantum computing fields and extreme environment electronics with the University of Science and Technology of China (USTC) alongside my research on quantum transport and its applications. This includes the design and manufacturing process of nanostructure devices. Meanwhile, my group focuses on measurement and control systems for quantum chips, specifically the semiconductor gate quantum dot, using GaAs, Si, graphene, and other 2-D materials. The work in our submitted Electronics Letters paper focuses on cryogenic electronics, including electron devices and circuits which operate at cryogenic temperatures. This temperature range extends from −150°C (123.15 Kelvin) down to absolute zero (0 K or −273.15°C). Cryogenic electronics have good prospects in applications such as space exploration, infrared focal plane array, quantum computing and many fields where electronics face extreme low temperature environments. A quantum computer comprises a quantum processor and a classical electronic control system. The quantum processor works in a dilution refrigerator at deep cryogenic temperatures down to the millikelvin range, while traditional electronic readout and control systems are implemented using room-temperature (RT) laboratory instruments. The cryogenic complementary metal oxide semiconductor (Cryo-CMOS) technology can greatly reduce noises generated by classical electronics and thermal environment, thus enhancing the fidelity and precision of quantum information processing. The first problem to solve when designing Cryo-CMOS circuits is transistor modelling. In answer to this we present the first compact model for 0.18 µm CMOS technology based on BSIM3 down to liquid Helium temperatures (4.2µK). We also present a sub-circuit model to improve the fitting precision at 4.2 K. This work provides experimental evidence for the implementation of cryogenic CMOS technology, a valid model of industrial tape-out process, and promotes the application of integrated circuits in cryogenic environments, for applications such as quantum measurement and for control systems for semiconductor quantum chips at very low temperatures. As it is difficult to build a low-temperature CMOS model by simply extracting parameters, this provided the motivation for us to establish a sub-circuit model to correct the kink deviations. In the short term, we can design and simulate cryogenic CMOS circuits using our model. In the longer term, cryo-CMOS can help us implement the cryogenic readout and control system for quantum computing. We plan to implement ADC (Analog-to-Digital Converter), DAC (Digital-to-Analog Converter), oscillator, FPGA (Field Programmable Gate Array), and other adaptive/passive integrated circuits at cryogenic temperatures or in irradiative environments. This involves research and progress in three main topics, namely: Cryo-CMOS characterization and modelling, Cryogenic integrated circuits on chips and Cryogenic circuits on boards. More and more researchers are beginning to pay attention to cryogenic electronics. With the current standard of, and growing pace of, development in quantum computing, cryogenic electronics will also receive faster development, and can be applied in future quantum computing and space exploration systems.

Threshold Voltage Modulation of a Graphene–ZnO Barristor Using a Polymer Doping Process

AbstractA method to modulate the threshold voltage of a graphene–ZnO barristor is investigated. Two types of polymers, polyethyleneimine (as an n‐type dopant) and poly (acrylic acid) (as a p‐type dopant), are used to pre‐set the initial Fermi level of the graphene. The threshold voltage of the graphene barristor can be modulated between −2.0 V (n‐type graphene) and 1.2 V (p‐type graphene) while modulating the Fermi level of the graphene by 120 meV. This process provides a scalable and facile method to adjust the threshold voltage of graphene–semiconductor junction‐based devices, which is a crucial function required to implement graphene‐based electronic devices in integrated circuits.

Graphene–semiconductor heterojunction sheds light on emerging photovoltaics

Electronic coupling of graphene atop a bulk semiconductor and the resultant interfacial energy-band reorganization create a light-sensitive junction only one atom below the front surface. Uniquely, this architecture leads to the surface being in extremely close proximity to the depletion region (typically buried several micrometres under the surface for a conventional wafer-based p–n junction solar cell), thus providing direct access to the photosensitive junction, which can be modified by surface functionalization and/or incorporation of plasmonic nanoparticles. The surface-based heterojunction, tunable carrier transport and relatively enhanced optical absorption in such 2D-layer-interfaced 3D semiconductor systems will have a transformative impact in the field of 2D optoelectronics, photovoltaics, photonics and nanoelectronics. Graphene-on-bulk semiconductors may enable new directions for ultrathin optoelectronics and photovoltaics.

GaN‐Based Nanorods/Graphene Heterostructures for Optoelectronic Applications

The insulating character of sapphire, meltback etching of Si, bulk and surface defects prevented the efficient integration of GaN nanostructures in optoelectronic devices. Here, it is demonstrated that graphene can simultaneously serve as an electrical bottom contact, a chemically inert buffer layer, and a superior lattice and thermal matched growth substrate. Vertically aligned, high crystal quality GaN nanorods (NRs) without bulk defects such as threading dislocations and with only a mild strain at the NRs’ base are grown by metal‐organic vapor‐phase epitaxy on defect‐free graphene using nanometer‐sized AlxGa1−xN nucleation islands. Here no influence of the supporting substrate on the GaN epitaxy is observed. However, at defects in graphene the effects of dangling bonds and the underlying substrate, presumably through nanoholes in graphene, on the properties of GaN NRs are visible. It is also shown that surface defects in InxGa1−xN/GaN NRs from planar films produced by etching of the defective material can be effectively passivated with only 10 nm alumina deposited by atomic layer deposition. This is confirmed by the increase in electroluminescence measured on finished devices with graphene top contact. These results can potentially lead to new material combinations including graphene, GaN, and other relevant semiconductors like Si toward yet unexplored device concepts.

A cathodic photovoltammetric sensor for chloramphenicol based on BiOI and graphene nanocomposites

A visible light-activated photocathode fabricated with p-type semiconductor bismuth oxyiodide (BiOI) and graphene (G) was employed to investigate the photovoltammetric behavior of chloramphenicol (CAP). The result indicated that the voltammetric reduction peak of CAP increased to a limiting current platform under photoirradiation, owing to photoelectrocatalytic reduction of CAP on the BiOI-G photocathode. As a result, the cathodic photovoltammogram became sigmoidal in shape. Furthermore, the influences of graphene content in BiOI-G composites, scan rate and light intensity on the photovoltammetric behavior of CAP on the BiOI-G photocathode were systematically investigated. Based on such a BiOI-G electrode, a cathodic photovoltammetric sensor for CAP was proposed, which exhibited a current response linearly proportional to CAP concentration in the range of 0.5–50 μmol L−1, with a detection limit (3S/N) of 0.14 μmol L−1. Moreover, the photovoltammetric sensor displayed good reproducibility and high stability. The applicability of the proposed sensor was demonstrated by determining CAP in eye drop and environmental water samples.

Nanostructured Active Media for Volatile Organic Compounds Abatement: the Synergy of Graphene Oxide and Semiconductor Coupling

Among the semiconductor-mediated photoprocesses, gas-phase photocatalytic decomposition of volatile organic compounds represents one of the most valid and feasible options for improving air quality. The present work is meant to show the preparation, characterization, and testing of photocatalytic systems for enhancing the performance of TiO2-based nanostructured membranes, namely, the coupling of semiconductors and addition of cocatalysts. In particular, the use of an additional semiconductor (Ag2CO3) and coupling of graphene oxide have been found to be promising for this purpose. All of the photocatalytic media have been tested in a specifically designed photoreactor with respect to the abatement of acetaldehyde and methanol in the gas phase; the obtained results showed complete degradation of 1600 ppm of acetaldehyde and 600 ppm of methanol in less than 15 and 40 min, respectively. The morphology of the nanostructured membranes and affinity of the catalytic system with the polymeric matrix have been fou...

Deposition of Sorption and Photocatalytic Material on Nanofibers and Fabric by Controlled Sublimation

This paper presents a new method of deposition of photocatalytic sorbent on nanofibers. This deposition uses controlled sublimation of water molecules from the vacuum-gel that is patent-protected. Silica gel nanostructures are precipitated by heterogeneous nucleation on the surface of nanofibres from an aqueous suspension of silicate nanoparticles and semiconductor carbon nitride (C3N4) or graphene nanosheets. After rapid solidification of gel (at least 104K/s), the nanofibers coated with the silica gel dispersion C3N4, or graphene are subjected to controlled sublimation at – 41 °C. This technology produced a nanofibrous material, which is stably coated with a highly porous silicate sorbent including dispersed photocatalytic nanoparticles. This textile material has a total sorption surface area of the order of hundreds m2/g. Unlike conventional sorbents, it is capable due to dispersed photocatalytic nanoparticles to regenerate sorption capacity by the absorption of visible light. The results of the preliminary research confirmed the high application potential of new controlled sublimation technology in the production of regenerable photocatalytic sorption fabrics.

Novel graphene enhancement nanolaser based on hybrid plasmonic waveguides at optical communication wavelength**Project supported by the Guangxi Natural Science Foundation, China (Grant No. 2017GXNSFAA198261), the National Natural Science Foundation of China (Grant No. 61762018), the Guangxi Youth Talent Program, China (Grant No. F-KA16016), the Guangxi Normal University Key Program, China (Grant No. 2015ZD03), the Innovation Project of Guangxi Graduate Education,

Surface plasmon polariton (SPP) nanolaser, which can achieve an all-optical circuit, is a major research topic in the field of micro light source. In this study, we examine a novel SPP graphene nanolaser in an optoelectronic integration field. The proposed nanolaser consists of metallic silver, two-dimensional (2D) graphene and high refractive index semiconductor of indium gallium arsenide phosphorus. Compared with other metals, Ag can reduce the threshold and propagation loss. The SPP field, excited by coupling Ag and InGaAsP, can be enhanced by the 2D material of graphene. In the proposed nanolaser, the maximum value of propagation loss is approximately 0.055 dB/μm, and the normalized mode area is constantly less than 0.05, and the best threshold can achieve 3380 cm−1 simultaneously. Meanwhile, the proposed nanolaser can be fabricated by conventional materials and work in optical communication (1550 nm), which can be easily achieved with current nanotechnology. It is also an important method that will be used to overcome the challenges of high speed, miniaturization, and integration in optoelectronic integrated technology.

Printed Electronics Based on Inorganic Semiconductors: From Processes and Materials to Devices

Following the ever-expanding technological demands, printed electronics has shown palpable potential to create new and commercially viable technologies that will benefit from its unique characteristics, such as, large-area and wide range of substrate compatibility, conformability and low-cost. Through the last few decades, printed/solution-processed field-effect transistors (FETs) and circuits have witnessed immense research efforts, technological growth and increased commercial interests. Although printing of functional inks comprising organic semiconductors has already been initiated in early 1990s, gradually the attention, at least partially, has been shifted to various forms of inorganic semiconductors, starting from metal chalcogenides, oxides, carbon nanotubes and very recently to graphene and other 2D semiconductors. In this review, the entire domain of printable inorganic semiconductors is considered. In fact, thanks to the continuous development of materials/functional inks and novel design/printing strategies, the inorganic printed semiconductor-based circuits today have reached an operation frequency up to several hundreds of kilohertz with only a few nanosecond time delays at the individual FET/inverter levels; in this regard, often circuits based on hybrid material systems have been found to be advantageous. At the end, a comparison of relative successes of various printable inorganic semiconductor materials, the remaining challenges and the available future opportunities are summarized.

Waveguide-based electro-absorption modulator performance: comparative analysis.

Electro-optic modulators perform a key function for data processing and communication. Rapid growth in data volume and increasing bits per second rates demand increased transmitter and thus modulator performance. Recent years have seen the introduction of new materials and modulator designs to include polaritonic optical modes aimed at achieving advanced performance in terms of speed, energy efficiency, and footprint. Such ad hoc modulator designs, however, leave a universal design for these novel material classes of devices missing. Here we execute a holistic performance analysis for waveguide-based electro-absorption modulators and use the performance metric switching energy per unit bandwidth (speed). We show that the performance is fundamentally determined by the ratio of the differential absorption cross-section of the switching material's broadening and the waveguide effective mode area. We find that the former shows highest performance for a broad class of materials relying on Pauli-blocking (absorption saturation), such as semiconductor quantum wells, quantum dots, graphene, and other 2D materials, but is quite similar amongst these classes. In this respect these materials are clearly superior to those relying on free carrier absorption, such as Si and ITO. The performance improvement on the material side is fundamentally limited by the oscillator sum rule and thermal broadening of the Fermi-Dirac distribution. We also find that performance scales with modal waveguide confinement. Thus, we find highest energy-bandwidth-ratio modulator designs to be graphene, QD, QW, or 2D material-based plasmonic slot waveguides where the electric field is in-plane with the switching material dimension. We show that this improvement always comes at the expense of increased insertion loss. Incorporating fundamental device physics, design trade-offs, and resulting performance, this analysis aims to guide future experimental modulator explorations.

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics.

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high- k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum dot arrays, carbon nanotubes, graphene, and other 2D semiconductors. Since thin-film transistors (TFTs) are the key enablers of FSE devices, we discuss TFT structures and operation mechanisms after a discussion on the needs and general requirements of gate dielectrics. Also, the advantages of high- k dielectrics over low- k ones in TFT applications were elaborated. Next, after presenting the design and properties of high- k polymers and inorganic, electrolyte, and hybrid dielectric families, we focus on the most important fabrication methodologies for their deposition as TFT gate dielectric thin films. Furthermore, we provide a detailed summary of recent progress in performance of FSE TFTs based on these high- k dielectrics, focusing primarily on emerging semiconductor types. Finally, we conclude with an outlook and challenges section.

Dirac electrons in quantum rings

We consider quantum rings realized in materials where the dynamics of charge carriers mimics that of two-dimensional (2D) Dirac electrons. A general theoretical description of the ring-subband structure is developed that applies to a range of currently available 2D systems, including graphene, transition-metal dichalcogenides, and narrow-gap semiconductor quantum wells. We employ the scattering-matrix approach to calculate the electronic two-terminal conductance through the ring and investigate how it is affected by Dirac-electron interference. The interplay of pseudo-spin chirality and hard-wall confinement is found to distinctly affect the geometric phase that is experimentally accessible in mesoscopic-conductance measurements. We derive an effective Hamiltonian for the azimuthal motion of charge carriers in the ring that yields deeper insight into the physical origin of the observed transport effects, including the unique behavior exhibited by the lowest ring subband in the normal and topological (i.e., band-inverted) regimes. Our work provides a unified approach to characterizing confined Dirac electrons, which can be used to explore the design of valley- and spintronic devices based on quantum interference and the confinement-tunable geometric phase.

On Image Charge Induced Barrier Lowering in Graphene–Semiconductor Contacts

Graphene has been extensively studied as highly flexible and optically transparent contacts in semiconductor devices, such as photodetectors, solar cells, and light emitting transistors. A Schottky barrier forms at the interface between graphene and semiconductor, whose height has an exponential impact on the current. In this work, image-charge-induced barrier lowering (BL) in graphene–semiconductor contacts is examined and compared to that in metal Schottky contacts. The results show that despite graphene being a semimetal with vanishing density-of-states at the Dirac point, the image-charge-induced BL can be significant. Even in an undoped graphene–semiconductor contact, the BL value can be more than 50% of that of a metal Schottky contact. The ratio of BL in a graphene–semiconductor contact to that in a metal–semiconductor contact increases as the graphene doping density increases and as the semiconductor dielectric constant decreases. An empirical expression for estimating the image-charge-induced BL in graphene–semiconductor contacts is provided.

Electronic Collective Mode Behaviors in Doped and Gated Armchair-Type Graphene Nanoribbons

Motivated by the recent nanophotonic community, in this work, we address the behavior of quantized charge-density fluctuations of doped and gated semiconductor armchair-type graphene nanoribbons within the tight-binding model and the Green’s function technique. In particular, we study the behavior of frequency-dependent susceptibility, when the system is exposed to photons or electrons. Injecting electrons by doping or ejecting ones by gating lead to different treatments in response function. Doping offers new collective modes due to added states between the valence and conduction bands (provided by the density of states) corresponding to intraband transitions, while gating distributes intraband modes. The results show that both ribbon width and doping concentrations affect the intraband transitions in electro-optical devices. Another remarkable point is the strong sensitivity of intraband plasmons to the direction of incoming photons or electrons. We found that the susceptibility of doped nanoribbons vanishes at perpendicular angles due to the distribution of intraband modes.

Interlayer coupling and electric field tunable electronic properties and Schottky barrier in a graphene/bilayer-GaSe van der Waals heterostructure.

In this work, using density functional theory we investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field. At the equilibrium state, the graphene is bound to bilayer-GaSe by a weak van der Waals interaction with the interlayer distance d of 3.40 Å with the binding energy per carbon atom of -37.71 meV. The projected band structure of the graphene/bilayer-GaSe heterostructure appears as a combination of each band structure of graphene and bilayer-GaSe. Moreover, a tiny band gap of about 10 meV is opened at the Dirac point in the graphene/bilayer-GaSe heterostructure due to the sublattice symmetry breaking. The band gap opening in graphene makes it suitable for potential applications in nanoelectronic and optoelectronic devices. The graphene/bilayer-GaSe heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.72 eV at the equilibrium interlayer spacing. Furthermore, a transformation from the n-type to p-type Schottky contact could be performed by decreasing the interlayer distance or by applying an electric field. This transformation is observed when the interlayer distance is smaller than 3.30 Å, or when the applied positive external electric field is larger than 0.0125 V Å-1. These results are very important for designing new electronic Schottky devices based on graphene and other 2D semiconductors such as a graphene/bilayer-GaSe heterostructure.