Electrostatically Reversible Polarity of Ambipolar α-MoTe2 Transistors

A doping-free transistor made of ambipolar α-phase molybdenum ditelluride (α-MoTe2) is proposed in which the transistor polarity (p-type and n-type) is electrostatically controlled by dual top gates. The voltage signal in one of the gates determines the transistor polarity, while the other gate modulates the drain current. We demonstrate the transistor operation experimentally, with electrostatically controlled polarity of both p- and n-type in a single transistor.

Doping-Free Complementary Logic Gates Enabled by Two-Dimensional Polarity-Controllable Transistors

Atomically thin two-dimensional (2D) materials belonging to transition metal dichalcogenides, due to their physical and electrical properties, are an exceptional vector for the exploration of next-generation semiconductor devices. Among them, due to the possibility of ambipolar conduction, tungsten diselenide (WSe₂) provides a platform for the efficient implementation of polarity-controllable transistors. These transistors use an additional gate, named polarity gate, that, due to the electrostatic doping of the Schottky junctions, provides a device-level dynamic control of their polarity, that is, n- or p-type. Here, we experimentally demonstrate a complete doping-free standard cell library realized on WSe₂ without the use of either chemical or physical doping. We show a functionally complete family of complementary logic gates (INV, NAND, NOR, 2-input XOR, 3-input XOR, and MAJ) and, due to the reconfigurable capabilities of the single devices, achieve the realization of highly expressive logic gates, such as exclusive-OR (XOR) and majority (MAJ), with fewer transistors than possible in conventional complementary metal-oxide-semiconductor logic. Our work shows a path to enable doping-free low-power electronics on 2D semiconductors, going beyond the concept of unipolar physically doped devices, while suggesting a road to achieve higher computational densities in two-dimensional electronics.

Contact Engineering of Molybdenum Ditelluride Field Effect Transistors through Rapid Thermal Annealing

Understanding and engineering the interface between metal and two-dimensional materials are of great importance to the research and development of nanoelectronics. In many cases the interface of metal and 2D materials can dominate the transport behavior of the devices. In this study, we focus on the metal contacts of MoTe₂ (molybdenum ditelluride) FETs (field effect transistors) and demonstrate how to use post-annealing treatment to modulate their transport behaviors in a controlled manner. We have also carried out low temperature and transmission electron microscopy studies to understand the mechanisms behind the prominent effect of the annealing process. Changes in transport properties are presumably due to anti-site defects formed at the metal-MoTe₂ interface under elevated temperature. The study provides more insights into MoTe₂ field effect devices and suggests guidelines for future optimizations.

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

Atomic Layer MoTe2 Field-Effect Transistors and Monolithic Logic Circuits Configured by Scanning Laser Annealing

Atomically thin semiconductors such as transition metal dichalcogenides have recently enabled diverse devices in the emerging two-dimensional (2D) electronics. While scalable 2D electronics demand monolithic integrated circuits consisting of complementary p-type and n-type transistors, conventional p-type and n-type doping in desired regions, monolithically in the same semiconducting atomic layers, remains elusive or impractical. Here, we report on an agile, high-precision scanning laser annealing approach to realizing 2D monolithic complementary logic circuits on atomically thin MoTe₂, by reliably designating p-type and n-type transport polarity in the constituent transistors via localized laser annealing and modification of their Schottky contacts. Pristine p-type field-effect transistors (FETs) transform into n-type ones upon controlled laser annealing on their source/drain gold electrodes, exhibiting a mobility of 96.5 cm² V^-1 s^-1 (the highest known to date) and an On/Off ratio of 10⁶. Elucidation and validation of such an on-demand configuration of polarity in MoTe₂ FETs further enable the construction and demonstration of essential logic circuits, including both inverter and NOR gates. This dopant-free, spatially precise scanning laser annealing approach to configuring monolithic complementary logic integrated circuits may enable programmable functions in 2D semiconductors, exhibiting potential for additively manufactured, scalable 2D electronics.

Reconfigurable Two-Dimensional Air-Gap Barristors

Reconfigurable logic circuits implemented by two-dimensional (2D) ambipolar semiconductors provide a prospective solution for the post-Moore era. It is still a challenge for ambipolar nanomaterials to realize reconfigurable polarity control and rectification with a simplified device structure. Here, an air-gap barristor based on an asymmetric stacking sequence of the electrode contacts was developed to resolve these issues. For the 2D ambipolar channel of WSe₂, the barristor can not only be reconfigured as an n- or p-type unipolar transistor but also work as a switchable diode. The air gap around the bottom electrode dominates the reconfigurable behaviors by widening the Schottky barrier here, thus blocking the injection of both electrons and holes. The electrical performances can be improved by optimizing the electrode materials, which achieve an on/off ratio of 10⁴ for the transistor and a rectifying ratio of 10⁵ for the diode. A complementary inverter and a switchable AND/OR logic gate were constructed by using the air-gap barristors as building blocks. This work provides an efficient approach with great potential for low-dimensional reconfigurable electronics.

The coordination of spindle-positioning forces during the asymmetric division of the Caenorhabditis elegans zygote

In Caenorhabditis elegans zygote, astral microtubules generate forces essential to position the mitotic spindle, by pushing against and pulling from the cortex. Measuring microtubule dynamics there, we revealed the presence of two populations, corresponding to pulling and pushing events. It offers a unique opportunity to study, under physiological conditions, the variations of both spindle-positioning forces along space and time. We propose a threefold control of pulling force, by polarity, spindle position and mitotic progression. We showed that the sole anteroposterior asymmetry in dynein on-rate, encoding pulling force imbalance, is sufficient to cause posterior spindle displacement. The positional regulation, reflecting the number of microtubule contacts in the posterior-most region, reinforces this imbalance only in late anaphase. Furthermore, we exhibited the first direct proof that dynein processivity increases along mitosis. It reflects the temporal control of pulling forces, which strengthens at anaphase onset following mitotic progression and independently from chromatid separation. In contrast, the pushing force remains constant and symmetric and contributes to maintaining the spindle at the cell centre during metaphase.

Co-solvent polarity controlled self-assembly of tetraphenylethylene-buried amphiphile for size-regulated tumor accumulation

We report that the co-solvent polarity can precisely control the TPE-buried amphiphile 1 to self-assemble into nanoparticles (NPs) in water with size range from ∼21–32 nm to 55–68 nm to 95–106 nm. Excepted for size, these TPE-buried amphiphile fabricated NPs hold identical physical properties such as spherical shape, surface charge, and luminescent properties, and moreover, after covalent capture of the acrylate hydrophilic heads, the resulting cross-linked NPs (cNPs I–III) own excellent in vivo stability, which thus would be an ideal platform for investigating the size effects on tumor accumulation and penetration.

Reconfiguration of operation modes in silicon nanowire field-effect transistors by electrostatic virtual doping

In this study, we perform reconfigurable n- and p-channel operations of a tri-top-gate field-effect transistor (FET) made of a p⁺-i-n⁺silicon nanowire (SiNW). In the reconfigurable FET (RFET), two polarity gates and one control gate induce virtual electrostatic doping in the SiNW channel. The polarity gates are electrically connected to each other and program the channel type, while the control gate modulates the flow of charge carriers in the SiNW channel. The SiNW RFET features simple device design, symmetrical electrical characteristics in the n- and p-channel operation modes using p⁺-i-n⁺diode characteristics, and both operation modes exhibit high ON/OFF ratios (∼10⁶) and high ON currents (∼1μAμm^-1). The proposed device is demonstrated experimentally using a fully CMOS-compatible top-down processes.

Polarity Control of ZnO Films Grown on Ferroelectric (0001) LiNbO3 Substrates without Buffer Layers by Pulsed-Laser Deposition

For this study, polarity-controlled ZnO films were grown on lithium niobate (LiNbO₃) substrates without buffer layers using the pulsed-laser deposition technique. The interfacial structure between the ZnO films and the LiNbO₃ was inspected using high-resolution transmission electron microscopy (HR-TEM) measurements, and X-ray diffraction (XRD) measurements were performed to support these HR-TEM results. The polarity determination of the ZnO films was investigated using piezoresponse force microscopy (PFM) and a chemical-etching analysis. It was verified from the PFM and chemical-etching analyses that the ZnO film grown on the (+z) LiNbO₃ was Zn-polar ZnO, while the O-polar ZnO occurred on the (-z) LiNbO₃. Further, a possible mechanism of the interfacial atomic configuration between the ZnO on the (+z) LiNbO₃ and that on the (-z) LiNbO₃ was suggested. It appears that the electrostatic stability at the substrate surface determines the initial nucleation of the ZnO films, leading to the different polarities in the ZnO systems.

Precisely Tailoring WSe2 Polarity via van der Waals Bismuth-Gold Modulated Contact

Creating high-quality contacts between high-melting-point metals and delicate two-dimensional (2D) semiconductors poses a critical challenge to polarity control due to inevitable chemical disorder and Fermi-level pinning observed in the contact regions. Here, we report a van der Waals (vdW) integration strategy to precisely tailor the WSe2 polarity by meticulously modulating metal contact compositions. Controlling the low-melting-point bismuth (Bi) thickness effectively modulates the Bi/Au dominant contact with WSe2. This facilitates the precise polarity transformation between n-type, ambipolar, and p-type, with exceptional field-effect mobilities of 200 cm2 V-1 s-1 for electrons and 136 cm2 V-1 s-1 for holes. Within this vdW geometry, we further demonstrate the fundamental electrical components such as diodes and complementary inverters with enhanced rectification ratios and voltage gains. Our results showcase an effective and compatible with mass manufacturing method for precise polarity modulation of 2D semiconductors, providing a promising pathway toward large-scale high-performance 2D electronics and integrated circuits.

Polarity Control within One Monolayer at ZnO/GaN Heterointerface: (0001) Plane Inversion Domain Boundary

In semiconductor heterojunction, polarity critically governs the physical properties, with an impact on electronic or optoelectronic devices through the presence of pyroelectric and piezoelectric fields at the active heteropolar interface. In the present work, the abrupt O-polar ZnO/Ga-polar GaN heterointerface was successfully achieved by using high O/Zn ratio flux during the ZnO nucleation growth. Atomic-resolution high-angle annular dark-field and bright-field transmission electron microscopy observation revealed that this polarity inversion confines within one monolayer by forming the (0001) plane inversion domain boundary (IDB) at the ZnO/GaN heterointerface. Through theoretical calculation and topology analysis, the geometry of this IDB was determined to possess an octahedral Ga atomic layer in the interface, with one O/N layer symmetrically bonded at the tetrahedral site. The computed electronic structure of all considered IDBs revealed a metallic character at the heterointerface. More interestingly, the presence of two-dimensional (2D) hole gas (2DHG) or 2D electron gas (2DEG) is uncovered by investigating the chemical bonding and charge transfer at the heterointerface. This work not only clarifies the polarity control and interfacial configuration of the O-polar ZnO/Ga-polar GaN heterojunction but, more importantly, also gives insight into their further application on heterojunction field-effect transistors as well as hybrid ZnO/GaN optoelectronic devices. Moreover, such polarity control at the monolayer scale might have practical implications for heterojunction devices based on other polar semiconductors.