Emre Yengel

Contact engineering for two-dimensional (2D) field effect transistors (FETs) has advanced rapidly, with near-quantum-limit contact resistances (R_C) now reported for top contacts formed by physical vapor deposition (PVD) techniques. However, top contacts are inherently scaling-unfriendly because they are limited by transfer-length (L_T). As contact length (L_C) shrinks below L_T, current crowding inflates R_C, constraining footprint scaling. Furthermore, this contact geometry is also ill-matched to stacked nanosheet and gate all around (GAA) transistor technology, which demands tier-addressable, minimal-footprint contacts, i.e., edge contacts. Early reports on edge contact to 2D materials involve PVD approaches with minimal control on the contact/2D interface. Here we introduce a scalable, chemistry-defined edge-contact platform based on atomic layer deposition (ALD) of metallic transition-metal chalcogenides, which exploits the intrinsic reactivity contrast between inert 2D basal planes and under-coordinated edges. Using ALD-grown TiS2 as a prototype, we form conformal edge contacts to wafer-scale monolayer MoS2, WS2, MoSe2 and WSe2, as well as to a multi-tier MoS2 nanosheet stack, illustrating natural compatibility with 2D GAA geometries. For TiS2–MoS2 edge contacts we obtain a contact resistance of ~130 kΩ·µm, consistent with a Schottky barrier of ~0.43 eV, and establish wafer-scale reproducibility through statistics on 100 n-type and 100 p-type devices. First-principles quantum-transport calculations both reproduce the measured barriers and identify alternative ALD-compatible metals that approach near-ohmic edge injection, while revealing that mode matching and edge termination are as critical as band alignment. Finally, complementary inverters assembled from MoS2/WSe2 edge-contacted FETs demonstrate functional logic with well-defined gain, noise margins and static power, positioning ALD-engineered edge contacts as a practical route to high-density 2D CMOS and 3D-integrated nanosheet technologies.

Growing continuous monolayer films of transition-metal dichalcogenides (TMDs) without the disruption of grain boundaries is essential to realize the full potential of these materials for future electronics and optoelectronics, but it remains a formidable challenge. It is generally believed that controlling the TMDs orientations on epitaxial substrates stems from matching the atomic registry, symmetry, and penetrable van der Waals forces. Interfacial reconstruction within the exceedingly narrow substrate-epilayer gap has been anticipated. However, its role in the growth mechanism has not been intensively investigated. Here, we report the experimental conformation of an interfacial reconstructed (IR) layer within the substrate-epilayer gap. Such an IR layer profoundly impacts the orientations of nucleating TMDs domains and, thus, affects the materials' properties. These findings provide deeper insights into the buried interface that could have profound implications for the development of TMD-based electronics and optoelectronics.

The massive deployment of fifth generation and internet of things technologies requires precise and high-throughput fabrication techniques for the mass production of radio frequency electronics. We use printable indium-gallium-zinc-oxide semiconductor in spontaneously formed self-aligned 100 GHz. Rectifier circuits constructed with these co-planar diodes can operate at ~47 GHz (extrinsic), making them the fastest large-area electronic devices demonstrated to date.

Neuromorphic computing has the potential to address the inherent limitations of conventional integrated circuit technology, ranging from perception, pattern recognition, to memory and decision-making ( Acc. Chem. Res. 2019, 52 (4), 964−974) ( Nature 2004, 431 (7010), 796−803) ( Nat. Nanotechnol. 2013, 8 (1), 13−24). Despite their low power consumption ( Nano Lett. 2016, 16 (11), 6724−6732), traditional two-terminal memristors can perform only a single function while lacking heterosynaptic plasticity ( Nanotechnology 2013, 24 (38), 382001). Inspired by the unconditioned reflex, multiterminal memristive transistors (memtransistor) were developed to realize complex functions, such as multiterminal modulation and heterosynaptic plasticity ( Nature 2018, 554, (7693), 500−504). Here we combine a hybrid metal halide perovskite with an organic conjugated polymer to form heterojunction transistors that are responsive to both electrical and optical stimuli. We show that the synergistic effects of photoinduced ion migration in the perovskite and electronic transport in the polymer layers can be exploited to realize memristive functions. The device combines reversible, nonvolatile conductance modulation with large switching current ratios, high endurance, and long retention times. Using in situ scanning Kelvin probe microscopy and variable-temperature charge transport measurement, we correlate the collective effects of bias-induced and photoinduced ion migration with the heterosynaptic behavior observed in this hybrid memtransistor. The hybrid heterojunction channel concept is expected to be applicable to other material combinations making it a promising platform for deployment in innovative neuromorphic devices of the future.