Molybdenum-sulfide-based optoelectronic device for multivalued logic

Two-dimensional (2D) anisotropic materials possess asymmetric atomic arrangements and normally exhibit physicochemical properties distinguishably along different crystal orientations, offering a brand-new degree of freedom for fabricating conceptual devices. Developing a feasible strain loading method for materials with nonorthogonal crystalline axes is necessary, enabling a deeper understanding of the 2D anisotropy of such materials, which is of valuable guidance for the optimization of optoelectronic devices. Here, we proposed a uniaxial strain loading method by rotation and examined the trend of optical properties of anisotropic ReS2 under strain applied along the a- and b-axis strain directions. From the Raman and photoluminescence spectra, it can be seen that the vibrational and optical responses achieve the maximum under the strain that is applied uniaxially along the crystalline b-axis. Our work provides a reliable strategy to tailor the anisotropic optical properties, making it feasible to selectively improve the material performance of ReS2 nanostructures-based optoelectronic and logic devices in the future.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have the potential to drive future innovation in the electronics industry. However, the controllability of charge concentration remains challenging due to the atomically thin channel, which perturbs the charge transport characteristics of nanodevices. Here, we demonstrate a strategy that uses the transition metal suboxide layer to modulate the photoelectrical characteristics of TMD channels. The carrier concentration in an n-type MoS2 channel is reduced from 2.05 × 1012 to 6.15 × 1010 cm−3, while it increases from 1.71 × 1010 to 2.76 × 1012 cm−3 for p-type WSe2 channels. Remarkably, the channel mobility remains unchanged or even slightly improves when the carrier concentration is appropriately tuned. Also, the homogenous channel is modulated into a photovoltaic homojunction with a tenfold enhancement of photoelectrical detectivity and response speed. The controllable strategy provides a simple design principle to realize high-performance 2D semiconductor-based optoelectronic and logic devices.

N- and p-type doping of transition-metal dichalcogenides by Ar plasma treatment and its application in CMOS

Materials obtained by immobilization of nickel and iron complexes on the surface of n-type titanium dioxide and p-type copper iodide have interesting photoelectrochemical properties. Fe(NA)Cl2@TiO2, Fe(NA)Cl2@CuI, Ni-rutin@CuI and Ni-rutin@TiO2 exhibit pronounced photosensitization towards visible light and photoelectrodes prepared from these materials generate photocurrents over a broad light wavelength window. The polarity of the generated photocurrents varies with change of the applied potential. Photocurrent switching phenomena can be described in terms of photoinduced charges transfer involving semiconductor and excited metal complex. Various types of interaction between semiconductor and adsorbed complex reflected in different mechanism of photosensitization. The studied materials has been characterized using various spectroscopic, crystallographic and electrochemical methods. Based on the photochemical measurements and diffuse reflectance spectroscopy the mechanism of photosensitization as well as mechanism of photocurrent generation in various conditions have been suggested. Due to interesting photoelectrochemical properties, studied materials are promising for optoelectronic logic devices such as demultiplexer. Studied materials are particularly attractive due to high stability and photostability.

Recent advances in optical bistability in a variety of materials and devices offer the potential for high speed operation over extended ranges of wavelength and temperature. The advantages of optoelec-tronic devices and multiple-valued logic are combined in various multistable solid-state device techniques, of which negative resistance multistability is most compatible with utilization of bistable optoelec-tronic devices. Additional stable states result from negative resistance interactions and facilitate implementation of variable radix analog and digital applications. Needed characteristics of bistable optical devices are outlined for compatibility with multiple-valued logic implementation. Multiple-valued optical logic offers synergistic potential for improved performance.

The semiconductor community is developing three-dimensional circuits that integrate logic, memory, optoelectronic and radio-frequency devices, and microelectromechanical systems. These three-dimensional (3D) circuits pose important challenges for thermal management due to the increasing heat load per unit surface area. This paper theoretically studies 3D circuit cooling by means of an integrated microchannel network. Predictions are based on thermal models solving one-dimensional conservation equations for boiling convection along microchannels, and are consistent with past data obtained from straight channels. The model is combined within a thermal resistance network to predict temperature distributions in logic and memory. The calculations indicate that a layer of integrated microchannel cooling can remove heat densities up to 135W/cm2 within a 3D architecture with a maximum circuit temperature of 85°C. The cooling strategy described in this paper will enable 3D circuits to include greater numbers of active levels while exposing external surface area for functional signal transmission.

The ultimate usefulness of a number system depends on its implementation. Multiple-valued logic has been implemented in charge-coupled devices (CCD). In this technology, logic values are encoded as charge. For example, prototype four-valued logic devices have been implemented at the University of Twente (Enschede, Holland). Hitachi has implemented a 16-valued memory that stores the equivalent of 10/sup 6/ bits. CCD is more compact than any other VLSI technology. Although it is slower than CMOS (complementary metal oxide semiconductor), it is much faster than the disk and has the potential of replacing the disk. The use of multiple-valued logic in CCD increases its storage capacity significantly. Multiple-valued logic has also been implemented in current-mode CMOS.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Combining the electronic properties of graphene and molybdenum disulphide (MoS2) in hybrid heterostructures offers the possibility to create devices with various functionalities. Electronic logic and memory devices have already been constructed from graphene-MoS2 hybrids, but they do not make use of the photosensitivity of MoS2, which arises from its optical-range bandgap. Here, we demonstrate that graphene-on-MoS2 binary heterostructures display remarkable dual optoelectronic functionality, including highly sensitive photodetection and gate-tunable persistent photoconductivity. The responsivity of the hybrids was found to be nearly 1×10(10) AW(-1) at 130K and 5×10(8)AW(-1) at room temperature, making them the most sensitive graphene-based photodetectors. When subjected to time-dependent photoillumination, the hybrids could also function as a rewritable optoelectronic switch or memory, where the persistent state shows almost no relaxation or decay within experimental timescales, indicating near-perfect charge retention. These effects can be quantitatively explained by gate-tunable charge exchange between the graphene and MoS2 layers, and may lead to new graphene-based optoelectronic devices that are naturally scalable for large-area applications at room temperature.

The recent advancements in multivalued logic gates represent a rapid paradigm shift in semiconductor technology toward a new era of hyper Moore's law. Particularly, the significant evolution of materials is guiding multivalued logic systems toward a breakthrough gradually, whereby they are transcending the limits of conventional binary logic systems in terms of all the essential figures of merit, i.e., power dissipation, operating speed, circuit complexity, and, of course, the level of the integration. In this review, recent advances in the field of multivalued logic gates based on emerging materials to provide a comprehensive guideline for possible future research directions are reviewed. First, an overview of the design criteria and figures of merit for multivalued logic gates is presented, and then advancements in various emerging nanostructured materials—ranging from 0D quantum dots to multidimensional heterostructures—are summarized and these materials in terms of device design criteria are assessed. The current technological challenges and prospects of multivalued logic devices are also addressed and major research trends are elucidated.

Multiple-Valued Programmable Logic Devices in Quantum-DNA Computing

Constructing heterostructures and doping are valid ways to improve the optoelectronic properties of transition metal dichalcogenides (TMDs) and optimize the performance of TMDs-based photodetectors. Compared with transfer techniques, chemical vapor deposition (CVD) has higher efficiency in preparing heterostructures. As for the one-step CVD growth of heterostructures, cross-contamination between the two materials may occur during the growth process, which may provide the possibility of one-step simultaneous realization of controllable doping and formation of alloy-based heterostructures by finely tuning the growth dynamics. Here, 2H-1T' Mox Re(1- x ) S2 alloy-to-alloy lateral heterostructures are synthesized through this one-step CVD growth method, utilizing the cross-contamination and different growth temperatures of the two alloys. Due to the doping of a small amount of Re atoms in 2H MoS2 , 2H Mox Re(1- x ) S2 has a high response rejection ratio in the solar-blind ultraviolet (SBUV) region and exhibits a positive photoconductive (PPC) effect. While the 1T' Mox Re(1- x ) S2 formed by heavily doping Mo atoms into 1T' ReS2 will produce a negative photoconductivity (NPC) effect under ultraviolet (UV) laser irradiation. The optoelectronic property of 2H-1T' Mox Re(1- x ) S2 -based heterostructures can be modulated by gate voltage. These findings are expected to expand the functionality of traditional optoelectronic devices and have potential applications in optoelectronic logic devices. This article is protected by copyright. All rights reserved.

As silicon-based transistors have approached their physical limits, it is urgent to explore alternative materials with a suitable bandgap and high mobility for next generation electronic logic devices. Two‐dimensional (2D) materials have attracted significant attention in the last few years due to their potential exotic transport physics and technological applications in various fields, such as a significant device downscaling for high intensity integration. Recently, a variety of 2D materials have been explored, including graphene [1] and transition metal dichalcogenides (TMDs), e.g., MoS2 [2,3], WS2 [4], and PtSe2 [5-7]. Although most research has focused on TMDs, recently 2D layered metal monochalcogenides, e.g., GaSe, have attracted increasing interest as a result of their unique electronic properties, making this class of materials different from TMDs.GaSe crystal structure comprises vertically stacked Ga-Se-Se-Ga layers with relatively weak van der Waals interactions. There are two main GaSe polytypes which differ in the stacking sequence of the basis layer units. Side- and top-view schematics of β‐GaSe and ε‐GaSe are shown in Fig. 1a. In this study, the electronic structure of both GaSe layered material polytypes is investigated using density functional theory (DFT) as implemented in QuantumATK [8]. Brillouin-zone integrations were performed according to the Monkhorst-Pack scheme [9] with a density of approximately 10 k-points per angstrom. Geometry optimizations were performed with the convergence criterion of 0.02 eV/Å [10]. Van der Waals (vdW) interactions improve the structural and electronic properties description obtained by DFT calculations and is included in our calculations through D3 version of Grimme’s dispersion corrections [11].To provide an improved determination of the bandgap energies, the GW (G: Green's function and W: screened Coulomb interaction) method in conjunction with a many body perturbation theory (MBPT) correction could be used. However, GW technique is computationally very expensive and could be implemented for systems with very limited number of atoms [12,13]. Hence, for this study, methods such as Heyd-Scuseria-Ernzerhof (HSE) hybrid functional [14,15] and GGA-1/2 [16] methods were included in our model to achieve more accurate bandgap compared to the experimental values. The β‐GaSe exhibits a DFT-obtained direct bandgap of ~1 eV while the corrected value is 2 eV. ε‐GaSe, however, shows slight indirect bandgap of 0.8 eV (DFT) and 1.7 eV (corrected), with just 25 meV difference between the indirect gap and indirect gap.A double-gate Schottky barrier field-effect transistor (FET) consisting of Ti source and drain contacts and ultrathin GaSe channel is also investigated. Schematic of the FET is shown in Fig. 1b. The device performance analysis such as current-voltage characteristics, subthreshold slope, and on/off ratio are carried out by means of non-equilibrium Green’s function together with DFT Hamiltonian [17]. The output characteristic of the proposed device exhibits an ON/OFF current ratio of more than 7 orders of magnitude.The presence of point defects in ultrathin 2D films is largely inevitable [18], even under optimized synthesis conditions, which can be either engineered and considered as a useful feature, or undesirable. In either case, understanding the impacts of point defects on the electronic structure of 2D materials are required to allow application-based optimization. In this talk, to provide insight into the defect-induced modifications to the GaSe electronic properties, in particular the properties of the states associated with the defects, we will compare the band-structure of the pristine GaSe with the band-structure of the GaSe with Ge and Se vacancies, for both GaSe polytypes.We have also fabricated back-gated devices by mechanically exfoliating ultrathin GaSe flakes from bulk crystal onto oxide-on-Si substrate. Fig. 1c shows an SEM image of the device. Our experimental results demonstrate the basic transport characteristics of thin-film transistor, which may offer more opportunities for potential applications such as photodetectors, gas sensors, and optoelectronic devices, in addition to nanoelectronics FETs, due to GaSe large bandgap.

In order to better prepare students at Electronic Engineering courses, practical teaching of digital circuits requires didactic kits with technology as efficient as possible. Nowadays, the discipline called Digital Electronics, from the Electrical Engineering Course of Federal University of Uberlândia, employs Didactic Kits with TTL devices, a technology that has been abandoned by the factories. Within this context, this paper proposes a new Didactic Kit, to be used together with a Personal Computer, containing a programmable logic device, optoelectronic devices and switches.

Two-dimensional (2D) layered materials hold great promise for various future electronic and optoelectronic devices that traditional semiconductors cannot afford. 2D pnictogen, group-VA atomic sheet (including phosphorene, arsenene, antimonene, and bismuthene) is believed to be a competitive candidate for next-generation logic devices. This is due to their intriguing physical and chemical properties, such as tunable midrange bandgap and controllable stability. Since the first black phosphorus field-effect transistor (FET) demo in 2014, there has been abundant exciting research advancement on the fundamental properties, preparation methods, and related electronic applications of 2D pnictogen. Herein, we review the recent progress in both material and device aspects of 2D pnictogen FETs. This includes a brief survey on the crystal structure, electronic properties and synthesis, or growth experiments. With more device orientation, this review emphasizes experimental fabrication, performance enhancing approaches, and configuration engineering of 2D pnictogen FETs. At the end, this review outlines current challenges and prospects for 2D pnictogen FETs as a potential platform for novel nanoelectronics.

Review for "A Self-Powered Bi-Directional SnS2/SnSe Heterostructure for an All-in-One Optoelectronic Logic Device"