N-type Characteristics Research Articles

Imide-Functionalized Fluorenone and Its Cyanated Derivative Based n-Type Polymers: Synthesis, Structure-Property Correlations, and Thin-Film Transistor Performance.

The development of high-performance n-type polymer semiconductors is powered by the design and synthesis of electron-deficient building blocks with optimized physicochemical properties. By meticulously installing an imide group onto fluorene and its cyanated derivative, we report here two very electron-deficient building blocks, imide-functionalized fluorenone (FOI) and its cyanated derivative (FCNI), both featuring a deep-lying lowest unoccupied molecular orbital energy level down to -4.05 eV and highly coplanar framework, endowing them ideal units for constructing n-type polymers. Thus, a series of polymers are built from them, exhibiting unipolar n-type transport character with a highest electron mobility of 0.11 cm2 V-1 s-1 . Hence, FOI and FCNI offer a remarkable platform for accessing high-performance n-type polymers and the imide functionalization of appropriate (hetero)arenes is a powerful strategy for developing polymers with deep-lying LUMOs for n-type organic electronics.

Synthesis of Group VIII Magnetic Transition-Metal-Doped Monolayer MoSe2.

The limitation on the spintronic applications of van der Waals layered transition-metal dichalcogenide semiconductors is ascribed to the intrinsic nonmagnetic feature. Recent studies have proved that substitutional doping is an effective route to alter the magnetic properties of two-dimensional transition-metal dichalcogenides (TMDs). However, highly valid and repeatable substitutional doping of TMDs remains to be developed. Herein, we report group VIII magnetic transition metal-doped molybdenum diselenide (MoSe2) single crystals via a one-pot mixed-salt-intermediated chemical vapor deposition method with high controllability and reproducibility. The high-angle annular dark-field scanning transmission electron microscopy studies further confirm that the sites of Fe are indeed substitutionally incorporated into the MoSe2 monolayer. The Fe-doped MoSe2 monolayer with a concentration from 0.93% to 6.10% could be obtained by controlling the ratios of FeCl3/Na2MoO4. Moreover, this strategy can be extended to create Co(Ni)-doped MoSe2 monolayers. The magnetic hysteresis (M-H) measurements demonstrate that group VIII magnetic transition-metal-doped MoSe2 samples exhibit room-temperature ferromagnetism. Additionally, the Fe-doped MoSe2 field effect transistor shows n-type semiconductor characteristics, indicating the obtainment of a room-temperature dilute magnetic semiconductor. Our approach is universal in magnetic transition-metal substitutional doping of TMDs, and it inspires further research interest in the study of related spintronic and magnetoelectric applications.

High-performance n-type thin-film transistor based on bilayer MXene/semiconductor with enhanced electrons transport

Interfacial engineering at the dielectric/semiconductor interface is highly crucial for fabricating organic field-effect transistors with high performance. In this study, a bilayer MXene/semiconductor configuration is introduced to fabricate a high-performance n-type transistor, where electrical charges are formed and modulated at the SiO2/semiconductor interface, and MXene nanosheets serve as the primary electrical charge channel due to their high mobility and long lateral size. The electrical performance is optimized by adjusting the degree of connectivity of the MXene nanosheets. The proposed MXene/poly{[N,N′-bis(2-octyl-do-decyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200) transistors show boosted n-type characteristics, including a 100-fold increase in field-effect mobility, a large ON/OFF ratio of 104, and a small subthreshold swing of 0.65 V dec−1, all of which are significantly improved compared with single-layer N2200 transistors. The high performance of the two-dimensional MXene nanochannel is due to its electronegativity and high mobility. The electronegativity significantly enhances electron transfer from N2200 to the MXene channel, where they are efficiently transported along the MXene channel. Interestingly, the MXene/p-type semiconductor transistors show suppressed p-type performance because of the highly negative MXene nanosheets. Additionally, the proposed bilayer MXene/n-type semiconductor configuration shows a good configuration generality and improved performance. These findings demonstrate the feasibility of fabricating high-performance n-type transistors using a bilayer MXene/semiconductor combination.

Enhanced DFT insights of doped phosphorene: Structural and electronic considerations

The electronic properties and structural attributes of doped monolayer phosphorene using density functional theory (DFT) are demonstrated in the present work. The selected dopants are carbon (C), silicon (Si), oxygen (O) and sulphur (S). The band structure and density of states (DOS) analysis indicates transition from semiconducting to metallic nature. Moreover, the electron density and electron difference density spectra also support the above findings. The binding energy for the dopants’ are in the energy range −6 eV to −10 eV affirming feasibility of doping. After doping, the lattice remains undistorted and the associated structural properties are thoroughly investigated based on data analysis backed up with detailed explanations. Dopants impart n-type and p-type characteristics to the phosphorene structure based on their valence electronic configuration. The novel insights of these properties provide us with enhanced perspective of their behaviour and prospective applications. For better understanding, effect of varying concentration of each dopant onto the electronic properties is reported. It includes detailed study of bandstructure, DOS, binding energy and charge transferred of each dopant for each concentration value.

Semi-interpenetrating network of polymer semiconductor and tetrapod nanocrystal assemblies with balanced ambipolar transport

Most organic semiconductors exhibit p-type electrical characteristics, whereas inorganic semiconductor nanocrystals typically possess n-type characteristics. Therefore, in principle, blending these two different materials can yield ambipolar transport for both electron and hole conduction if a percolation pathway for each charge carrier can be developed within the blended material. As the dimensions of these materials are on the nanometer scale, forming such a percolation pathway is challenging. Herein, we report a solution-processed method to construct an ambipolar channel by combining tetrapod-shaped CdSe nanocrystals and polythiophene. A fully percolated network of tetrapod CdSe nanocrystals were first produced by benefitting from the extended geometry of the nanostructure with four arms. The voids of the network were then filled with polythiophene, leading to a semi-interpenetrating network containing percolation pathways for both electrons and holes. A balanced ambipolar transport was achieved with electron and hole conductivities of 10.6 S/cm and 16.2 S/cm, respectively. The hybridization strategy for organic/inorganic semiconductors presented herein provides an innovative route to prepare solution-processable thin films for both electron and hole transport electronic devices.

Effect of N doping on the Optical and Electrical properties of Thermal Spray pyrolysed ZnO Thin Films

Nitrogen doped ZnO (ZnO:N), thin films have been deposited on glass substrate at the temperature of 350ºC by low cost homemade thermal spray pyrolysis (TSP) technique at a normal environmental conditions. In this study the average reflectance, transmittance and absorbance were measured (20%), (35%), and (45%), respectively. Absorption coefficient is 3.5x104cm-1 for N doped ZnO. Direct bandgap energy varies from 3.08-2.99eV and indirect band gap energy varies from 2.86-2.67eV for N doped ZnO. XRD analysis shows the (002) plane is present of samples and the average grain size decrease with increasing N concentration. Surface morphology of N doped ZnO films is studied by Scanning Electron Microscopy (SEM). It is seen that hexagonal crystal grains few voids are present for N doped ZnO samples. The surface exhibits more or less uniform surface morphology with some clusters on the whole surface. Hall Effect study confirms that Nitrogen doped ZnO (ZnO:N), thin films using Vander pauws method were made at room temperature at a constant field of 9.75 KG. Experimentally (1, 2, 3, and 4) % N doped ZnO thin films have shown in negative Hall Constant (RH). Which exhibited n-type characteristics. Hall Constant (RH), and Hall concentration (n), increases with increasing N doping concentration. Initially Hall mobility (μH), increases linearly for (1-2) % N doping concentration then it decreases for the rest of the doping concentration. We also found that the resistivity (ρ) decreases and the conductivity (s) increases with increasing N doping concentration which exhibits the semiconducting nature.

Spontaneous Coassembly of the Protein Terthiophene into Fluorescent Electroactive Microfibers in 2D and 3D Cell Cultures

Protein-based microfibers are biomaterials of paramount importance in materials science, nanotechnology, and medicine. Here we describe the spontaneous in situ formation and secretion of nanostructured protein microfibers in 2D and 3D cell cultures of 3T3 fibroblasts and B104 neuroblastoma cells upon treatment with a micromolar solution of either unmodified terthiophene or terthiophene modified by mono-oxygenation (thiophene → thiophene S-oxide) or dioxygenation (thiophene → thiophene S,S-dioxide) of the inner ring. We demonstrate via metabolic cytotoxicity tests that modification to the S-oxide leads to a severe drop in cell viability. By contrast, unmodified terthiophene and the respective S,S-dioxide cause no harm to the cells and lead to the formation and secretion of fluorescent and electroactive protein–fluorophore coassembled microfibers with a large aspect ratio, a micrometer-sized length and width, and a nanometer-sized thickness, as monitored in real-time by laser scanning confocal microscopy (LSCM). With respect to the microfibers formed by unmodified terthiophene, those formed by the S,S-dioxide display markedly red-shifted fluorescence and an increased n-type character of the material, as shown by macroscopic Kelvin probe in agreement with cyclovoltammetry data. Electrophoretic analyses and Q-TOF mass spectrometry of the isolated microfibers indicate that in all cases the prevalent proteins present are vimentin and histone H4, thus revealing the capability of these fluorophores to selectively coassemble with these proteins. Finally, DFT calculations help to illuminate the fluorophore–fluorophore intermolecular interactions contributing to the formation of the microfibers.

Effects of Different Point Defects on the Electronic Properties of III–V Al0.5Ga0.5N Photocathode Nanowires

AlxGa1−xN nanowires are the key materials for next-generation ultraviolet (UV) detectors. However, such devices have a low quantum efficiency caused by the introduction of defects and impurities throughout the preparation process of nanowires. Herein, the effects of different interstitial defects and vacancy defects on the electronic structure of Al0.5Ga0.5N nanowires are investigated using density functional theory calculations. Our results successfully discovered that only the formation of an N interstitial defect is thermally stable. In addition, the introduction of different defects makes the different nanowires exhibit n-type or p-type characteristics. Additionally, different defects lead to a decrease in the conduction band minimum in band structures, which is the major cause for the decrease in work function and increase in electron affinity of Al0.5Ga0.5N nanowires. What is more, the calculation of the partial density of states also proved that the interstitial defects contribute to a re-hybridization of local electron orbitals and then cause more significant movement of the electron density. Our investigations provide theoretical guidance for the pursuit of higher-quantum-efficiency ultraviolet (UV) detectors.

Effect of intentional chemical doping on crystallographic and electric properties of the pyrochlore Bi2Sn2O7

The development of p-type oxide semiconductors is challenging owing to the localized nature of the valence band maximum (VBM), which primarily comprises O 2p orbitals. Although some Sn2+-based pyrochlore-type oxides (A2B2O7) with VBMs comprising spatially spread Sn 5s orbitals show p-type semiconducting properties, these properties cannot be tuned by an intentional chemical doping owing to the instability of their valence states. Herein, the influence of chemical doping on the crystal structure and electrical properties of Bi2Sn2O7, whose VBM is composed of valence-stable ions with Bi 6s orbitals, in the VBM is investigated. X-ray absorption spectroscopy reveals that In3+ is doped substitutionally at the Sn4+ site. Although the doped In3+ ions are expected to act as acceptors, their electrical properties always show n-type character. Simultaneously, extended X-ray absorption fine structure reveals the formation of oxygen vacancies in BiOBi bonds contributing to the VBM, whereas negligible changes are observed in the SnO6 octahedra, suggesting that the generated holes are electrically compensated by electrons because of the oxygen vacancies. P-type electric properties can be observed under oxidizing conditions, providing a critical design concept for the realization of hole conduction in acceptor-doped Bi2Sn2O7.

Versatile Solution-Processed Reductive Interface Layer for Contact Engineering of Staggered Organic Field-Effect Transistors

Efficient charge injection/extraction from/to contact electrodes is essential to realize organic electronic and optoelectronic devices with optimum characteristics for many applications. Herein, we studied a versatile reductive interlayer based on sodium borohydride (NaBH4) to control the contact properties of the staggered organic field-effect transistors (OFETs) either by doping and/or by regulating the contribution of charge carriers. The versatile functionalities of the NaBH4 layer are mainly determined by the alignment of frontier molecular orbitals of donor-acceptor (D-A) type copolymer semiconductors and the work function of the contact electrode. After incorporating the NaBH4 layer, the work function of the bottom-contact gold electrode can be decreased significantly by 1.0 eV, which makes it favorable to efficient electron injection. An Ohmic contact is achieved by the spontaneous injection of electrons to the n-type organic semiconductors with high electron affinity while converting the OFET operation mode to n-type characteristics by blocking the counter-charge carriers for the other types of ambipolar and p-type semiconductors. The solution-processed reducing agent can be a valuable approach to develop high-performance printed and flexible electronic devices through careful engineering to obtain proper contributions of charge carriers either as electrons or holes in various D-A copolymer semiconductors.

Effects of pH and Cl− Content on Degradation Process of Pre-Passivated Stainless Steels in an Alkaline Solution

The degradation behavior of four prepassivated stainless steels (SSs) in the alkaline solutions with different Cl− concentrations and pH values were investigated by cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis and the X-ray photoelectron spectroscopy (XPS). The results indicated that the pH value and Cl− concentration, together with the phase ratio difference in the microstructure of SS, played a critical role in the degradation process of passive film. At low pH and high Cl− concentration, the passive film gradually enriched in Fe3+ and Cr3+ species and depleted in Fe2+ oxides and its self-regeneration process became more difficult. As the pH decreased, the passive film exhibited clear n-type and p-type semiconductor characteristics more clearly, and the decrease in dopant density well reflected the changes in Fe2+/Fe3+ ratio and electrochemical behavior. Based on the viewpoint of adsorption balance between OH− with inhibitory effect and Cl− with promotion effect on the degradation process, a mechanism for the degradation process of prepassivation film was proposed.

Low-Temperature Microwave Processed TiO2 as an Electron Transport Layer for Enhanced Performance and Atmospheric Stability in Planar Perovskite Solar Cells

Low-temperature (∼150 °C) solution processed planar perovskite solar cells (PSCs) using TiO2 as an electron transport layer (ETL) offer promise for a simple fabrication methodology and compatibility with polymeric substrates and perovskite-based tandem devices. However, the amorphous nature and presence of trap states on the low-temperature TiO2 surface hinder the effective carrier transport. Further, perovskite crystallization on ETL develops lattice strain resulting in the creation of unwanted defect centers. Herein, a low-temperature microwave processed compact TiO2 (MW-TiO2) film is reported that possesses lower surface oxygen vacancy defects and enhanced conductivity and promotes efficient electron extraction owing to the enhanced built-in potential (Vbi) at the MW-TiO2/perovskite interface. The suppressed heterogeneous nucleation of MAPbI3 crystals on the less defective MW-TiO2 surface relieves the interfacial strain, thereby making it a superior template for the growth of strain relaxed, high-quality perovskite films with a more n-type character having larger grains, resulting in suppressed interfacial/surface and bulk trap density. Further, MW-TiO2 mitigates the interfacial energetic disorder and Urbach energy owing to reduced strain, thereby boosting the open-circuit voltage (Voc) by 40 mV, while improved optoelectronic properties of MW-TiO2, lower interfacial charge transfer resistance, and high-quality perovskite films simultaneously improve the short-circuit current density (Jsc) and fill factor (FF) by 6.82 and 9.37%, respectively, over HT-TiO2 based devices. Compared to high-temperature (500 °C) annealed TiO2 based MAPbI3 planar PSCs, MW-TiO2 based devices exhibited a substantial performance enhancement of 22%, leading to the best efficiency of ∼18% and superior atmospheric stability (25 °C, 55% relative humidity) while maintaining 80% of its initial value after 2500 h. Experimental results are validated by device simulation studies with model accounting for trap-assisted interfacial and bulk recombination. Finally, MW processed flexible devices maintained over 80% of their initial power conversion efficiency (PCE) after 1000 bending cycles, thereby exhibiting excellent mechanical robustness. These results elucidate the critical role of MW-TiO2 in rendering improved performance, flexibility, and stability in low-temperature PSCs.

Enhanced channel modulation in Aluminum- and Hydrogen-Doped Zinc-Oxide-Based transistors by complementary Dual-Gate operation

This study elucidates the enhanced channel modulation by the dual-gate operation of the ultrathin ZnO-based field-effect transistors (FETs). Bottom-gate atomic-layer-deposited zinc oxide (ZnO) transistors exhibit typical n-type enhancement-mode transfer characteristics. However, when equipped with the top Al2O3 layer, the FETs exhibit conductive transfer characteristics. These electrical property changes are attributed to Al2O3-induced hydrogen and aluminum doping effects, which increase carrier concentration. Although Al2O3-induced doping increased field-effect mobility by a factor of 2, a high off current and degraded transconductance swing were observed in FETs. However, operation in dual-gate mode after the deposition of the top-gate electrode resolved these degradations and led to achieving high-performance ZnO FETs: the off current significantly decreased, and noteworthy, field-effect mobility increased by a factor of 5. Temperature-dependent charge transport analysis revealed that the complementary dual-gate operation efficiently filled the localized trap states in the ZnO films, resulting in band-like transport. Thus, it is deduced that the complementary dual-gate operation enhanced channel modulation in the Al2O3-induced hydrogen- and aluminum-doped ZnO channel, resulting in high-performance ZnO FETs.

Understanding the Seebeck coefficient of LaNiO3 compound in the temperature range 300–620 K

Transition metal oxides have been attracted much attention in thermoelectric community from the last few decades. In the present work, we have synthesized LaNiO3 by a simple solution combustion process. To analyse the crystal structure and structural parameters we have used Rietveld refinement method wherein FullProf software is employed. The room temperature x-ray diffraction indicates the rhombohedral structure with space group (No. 167). The refined values of lattice parameters are a = b = c = 5.4071 Å. Temperature dependent Seebeck coefficient (S) of this compound has been investigated by using experimental and computational tools. The measurement of S is conducted in the temperature range 300–620 K. The measured values of S in the entire temperature range have negative sign that indicates n-type character of the compound. The value of S is found to be ∼−8 μV/K at 300 K and at 620 K this value is ∼−12 μV/K. The electronic structure calculation is carried out using DFT + U method due to having strong correlation in LaNiO3. The calculation predicts the metallic ground state of the compound. Temperature dependent S is calculated using BoltzTraP package and compared with experiment. The best matching between experimental and calculated values of S is observed when self-interaction correction is employed as double counting correction in spin-polarized DFT + U (=1 eV) calculation. Based on the computational results maximum power factors are also calculated for p-type and n-type doping of this compound.

Control of Charge Transport Properties in Molybdenum Diselenide Field-Effect Transistors for Enhanced Noise-Margin and Inverter Characteristics

Ambipolar field-effect transistor (FET) capable of transporting both holes and electrons has the advantage of operating as both p-type and n-type with a single device depending on the voltage bias condition. Among transition metal dichalcogenides (TMDs), molybdenum diselenide (MoSe₂), which has ambipolar properties, exhibits n-type dominant electrical characteristics. As a result, a digital inverter implemented only using pristine MoSe₂ FETs exhibited asymmetric and limited output swing characteristics because of the difficulty in pull-up operation. Therefore, a method for improving the p-type characteristics of MoSe₂ is needed to implement a complementary metal–oxide–semiconductor (CMOS)-like digital inverter using only MoSe₂. In this study, an n-type dominant MoSe₂ FET was adjusted to have p-type dominant characteristics through annealing process. Raman spectroscopy was used to compare the transistor with previous studies. Statistical analysis showed that the charge transport behavior was reproduced in multiple devices. The p-type enhanced MoSe₂ FET was applied as a pull-up transistor of a digital inverter to present the practicality of the annealing process to improve the p-type characteristics of the MoSe₂ FET. Eventually, a more symmetrical output swing and improved noise margin were achieved compared to a digital inverter composed of only n-type dominant MoSe₂ FETs.

Computational study of electron transport in halogen incorporated diindenotetracene compounds: crystal structure, charge transport and optoelectronic properties.

The crystal structure, charge transport and optoelectronic properties of newly designed air-stable halogenated diindenotetracene (DIT) based OSCs are reported in this article. The structural, electronic and charge transport properties of the compounds are investigated using density functional theory (DFT) formalism. The air-stability and n-type characteristics are validated from their low lying LUMO energies (<-3.9 eV) and large electron affinity (EA) values (>3.0 eV). Compared with the parent DIT, the designed DIT-X compounds (except for DIT-I) exhibit larger electronic coupling (Ve is found to be ∼1.5 times larger than that of the bare DIT) and higher electron mobilities because of the effect of electron-withdrawing groups substituted at the peripheral positions of the DIT derivatives. The designed DIT-X compounds (except DIT-I) show high electron mobilities (∼2.4-5.4 cm2 V-1 s-1), implying that the compounds can serve as promising electron transport materials. In addition, the UV-visible optical spectra of DIT derivatives (except DIT-F) display bathochromic shifts as compared to the bare DIT compound.

Deposition of the tin sulfide thin films using ALD and a vacuum annealing process for tuning the phase transition

Tin sulfide (SnSx) thin films deposited by atomic layer deposition (ALD) under various deposition conditions have unique properties. Such films have two phases, tin monosulfide (SnS) and tin disulfide (SnS2), that depend on the composition ratio of the thin film, and these materials can be applied to a wide range of technologies, such as solar cells, optical sensors, and transistors. In this study, we deposit amorphous tin sulfide thin films at 100 °C using ALD and perform post annealing at various temperatures to control the phase transition from SnS2 to SnS. The post annealing temperature-dependent phase transition was analyzed through Raman spectroscopy, grazing-incidence X-ray diffraction (GI-XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV–vis) spectroscopy, and ultraviolet photoelectron spectroscopy (UPS). Thermodynamic calculations were performed to determine that the initial temperature of the phase transition correspond to the post annealing temperature of 350 °C. The phases and crystal structures of the films annealed at different temperatures were investigated by Raman and GI-XRD. The chemical bonding of the films was analyzed through XPS, revealing that the binding energy of Sn4+ states shifted to the lower binding energy of Sn2+ states with increasing annealing temperatures. The electronic band structures of the films were calculated by UV–vis and UPS. The band gaps of the 300 °C, 350 °C, 400 °C annealed films were 2.26 eV, 2.05 eV, 1.63 eV, respectively. The tin sulfide thin films had n-type characteristics when annealed at 300 °C, which changed to p-type characteristics when annealed at 350 °C and 400 °C. Through this study, we can investigate phase transition of tin sulfides and correlate fabrication conditions to both n-type and p-type characteristics, which can be applied to synthesize the desired films for application in various devices.

End-Capping π-Conjugated Naphthodithiophene Diimide (NDTI)-Based Triads with Noncovalent Intramolecular S···O Interactions: A Route towards High-Performance Solution-Processable Air-Stable n-Type Semiconductors

Introducing noncovalent intramolecular interactions into functional π-conjugated organic molecules or polymers is a useful method to improve the performance of organic semiconducting devices. In this study, two small molecules based on naphthodithiophene diimide (NDTI), NDTI-BTIC1 and NDTI-BTIC2, were successfully designed and synthesized by covalently connecting an electron-deficient NDTI-core and two 3-(dicyanomethylidene)-indan-1-one (IC) groups with thiophene substituted by an alkoxy chain or alkyl chain, respectively. Density functional theory (DFT) calculations on the optimized geometries of the triads predict that the existence of noncovalent intramolecular S (thiophene)···O (alkoxy) interactions is possible in NDTI-BTIC1. The molecular orbital distributions of NDTI-BTIC1 and NDTI-BTIC2 show that the lowest unoccupied molecular orbitals (LUMOs) are delocalized in the whole molecule, implying the possibility to show n-type transport characteristics. The two molecules further demonstrated LUMOs at a low altitude of −4.37 to −4.45 eV, low enough for the stable transmission of electrons in the atmosphere. The solution-processing method was used to prepare transistors based on the two molecules’ bottom-gate top-contact (BGTC), which exhibited unipolar n-type field-effect transistor (FET) characteristics in the air. The FET performance of NDTI-BTIC1 is higher than that of NDTI-BTIC2 in both the as-spun and thermal annealed films, possibly attributed to the existence of noncovalent intramolecular S···O interactions in NDTI-BTIC1. Moreover, the maximum electron mobility of NDTI-BTIC1 obtained at 150 °C thermal annealing is improved by one order of magnitude compared to that of NDTI-BTIC2, being 0.17 and 0.085 cm2 V–1 s–1, respectively. The transport difference of the two molecules was proved by film morphology analysis. The results show that constructing noncovalent intramolecular S···O conformational locks between the TIC unit and NDTI can improve the organic field-effect transistor (OFET) devices’ performance through reasonable molecular design strategies.

Controlling Carrier Transport in Vertical MoTe2/MoS2 van der Waals Heterostructures.

Two-dimensional (2D) transition-metal dichalcogenide (TMDC)-based semiconducting van der Waals (vdW) heterostructures are considered as potential candidates for next-generation nanoelectronics due to their unique and tunable properties. Controlling the carrier type and band alignment in 2D TMDCs and their vdW heterostructures is critical for realizing heterojunctions with the desired performances and functionalities. In this report, controlling the carrier type and band alignment in a vertical MoTe2/MoS2 heterojunction is presented via thickness engineering and surface charge transfer doping. A highly rectifying p-n diode and a nonrectifying n-n junction are obtained with different MoTe2 thicknesses due to their different doping conditions. A vertical tunnel diode is subsequently achieved with a controlled oxygen plasma treatment, which selectively induces degenerate p-type doping to MoTe2, whereas the intrinsic n-type characteristic of MoS2 is maintained during the treatment. These techniques to realize multifunctional diodes are universal and applicable to emerging nanoelectronics based on 2D materials.

Flexible Transparent Electric-Double-Layer Junctionless Thin Film Transistors with Low Operating Voltage

Flexible transparent junctionless thin film transistors gated by microporous SiO2 dielectric with electric-double-layer (EDL) effect are fabricated onto PET substrates at room temperature. These devices exhibit high-performance n-type transistor characteristics operating in enhancement mode with low operating voltage of 1.5 V due to the huge gate specific capacitance (0.44 μF cm−2 at 40 Hz) related to EDL formation. The electron field-effect mobility of 28.4 cm2 V−1 s−1, current on/off ratio and the subthreshold swing are found to be 5 × 106 and 0.1 V decade−1, respectively. These achievements demonstrate that flexible transparent junctionless thin-film transistors are promising for the next-generation low-power flexible transparent electronics applications.