Toward Determination of the Critical Breakdown Field in Rutile Sn _{1‐ <i>x</i>} Ge _<i>x</i> O ₂ Alloys

physica status solidi (a) · 2026-03-15

The high‐field electronic transport characteristics of ultra‐wide bandgap (UWBG) rutile Sn 1‐ x Ge x O 2 alloys have been investigated through high‐voltage measurements using lateral metal–semiconductor–metal (MSM) structures. Undoped Sn 1‐ x Ge x O 2 thin films with a Ge composition of x ≈ 0.70 were epitaxially grown on c‐plane sapphire substrates via pulsed‐laser deposition at 650°C. MSM structures were fabricated using Pt contacts with contact spacings ranging from 0.5 to 2.7 μm to probe the voltage‐dependent transport behavior under high electric fields. The best devices demonstrated the ability to sustain applied voltages approaching 900 V prior to breakdown. Electrostatic simulations were used to evaluate the electric field distribution in the channel for the varying gap spacings and showed that the electric field in the channel is roughly three‐fourths of the applied voltage divided by the contact spacing, leading to an estimate of the critical breakdown field in the range of 7.0 ± 1.4 MV/cm. These results are encouraging that UWBG Sn 1‐ x Ge x O 2 alloys could have potential for applications in high‐power electronics.

Ultralow-Resistance Contacts to Heavily Doped p-Type Nb_<i>x</i>W_1–<i>x</i>S_<i>y</i> Thin Films Grown by Atomic Layer Deposition

ACS Applied Materials & Interfaces · 2025-02-06 · 3 citations

Transition metal dichalcogenides (TMDs) are an important class of materials for future microelectronics. Of particular interest are TMDs deposited by atomic layer deposition (ALD) since this technique allows both back-end-of-line (BEOL) compatible deposition and the ability to create heavily doped regions for contact formation. In this work, we characterize ∼3 nm-thick heavily doped NbxW1–xSy thin films grown by plasma-enhanced ALD using gated transfer-length measurement (TLM) structures. An analysis of films with different Nb concentrations, x, found that films with x = 0.22 had the lowest sheet resistivity of 86 kΩ/sq along with an ultrahigh carrier concentration of 4.2 × 1020 cm–3. The contact resistance, RC, of different metals to NbxW1–xSy thin films was also analyzed. Among Pd, Ni, and Ti contacts, Pd was found to have the lowest RC, whereas Ni (Ti) had an average RC that was 6× (20×) higher than Pd. Physical analysis of the films using Raman spectroscopy and transmission electron microscopy shows that the crystal quality degrades going from x = 0.08 to 0.33, while Kelvin probe force microscopy, complemented by density functional theory, is used to explain the Nb concentration of the extracted work function. The best TLM structures have an RC value as low as 0.30 ± 0.26 kΩ–μm and a mean specific contact resistivity, ρC, of 11 ± 27 nΩ-cm2. Even after accounting for experimental error, this value is lower than the other values reported for p-type TMD contacts in the literature. These results suggest that NbxW1–xSy can be a promising intermediate layer between metal contacts and monolayer WSe2 in future scaled-down TMD MOSFETs.

Ferroelectric Switching in Hybrid Molecular-Beam-Epitaxy-Grown BaTiO₃ Films

Nano Letters · 2025-09-20 · 2 citations

-based heterostructures grown by hybrid MBE for future electronic, photonic and spintronic applications.

A Strategic Approach for Enhanced p‐Type Doping of WSe₂ p‐MOSFETs Using an Atomic Oxidation Process

Advanced Electronic Materials · 2025-06-26

Abstract Doping allows precise tuning of the electronic properties in 2D materials, optimizing their performance for applications such as complementary metal‐oxide‐semiconductor (CMOS) technology. However, developing reliable p ‐type 2D semiconductors remains challenging due to intrinsic defects or unintentional n ‐type doping. This study presents robust p ‐type monolayer WSe 2 field‐effect transistors (FETs) using phase‐engineered WSe 2 /WSe y O x building blocks created via an atomic oxidation process (AOP). The findings reveal that when bilayer WSe 2 is exposed to AOP, the top layer undergoes self‐limited oxidation to WSe y O x with no detectable oxidation of the bottom layer. This result is confirmed by Raman spectroscopy, X‐ray photoelectron spectroscopy, and Kelvin probe force microscopy. This process has further been used to demonstrate a well‐controlled and fully encapsulated WSe y O x /WSe 2 /WSe y O x heterostructure, ensuring symmetrical protection and stability of the WSe 2 channel region. The surface charge transfer doping using WSe y O x provides the capability to selectively modulate the carrier concentration in a WSe 2 without altering the intrinsic properties of the channel. This non‐destructive method simplifies the fabrication of p ‐type 2D FETs with monolithic, phase‐engineered heterostructures, facilitating seamless integration into next‐generation device architectures.

Interfacial Strong Coupling and Negative Dispersion of Propagating Polaritons in Freestanding Oxide Membranes

Advanced Optical Materials · 2025-09-19 · 2 citations

Abstract Membranes of complex oxides like perovskite SrTiO 3 extend the multi‐functional promise of oxide electronics into the nanoscale regime of 2D materials. Here, it is demonstrated that freestanding oxide membranes supply a reconfigurable platform for nano‐photonics based on propagating surface phonon polaritons. Infrared near‐field imaging and spectroscopy enabled by a tunable ultrafast laser are applied to study pristine nano‐thick SrTiO 3 membranes prepared by hybrid molecular beam epitaxy. As predicted by coupled mode theory, it is found that strong coupling of interfacial polaritons realizes symmetric and antisymmetric hybridized modes with simultaneously tunable negative and positive group velocities. By resolving reflection of these propagating modes from membrane edges, defects, and substrate structures, their dispersion is quantified with position‐resolved nano‐spectroscopy. Remarkably, polariton negative dispersion is found to be both robust and tunable through choice of membrane dielectric environment and thickness, and proposes a novel design for in‐plane Veselago lensing harnessing this control. This work lays the foundation for tunable transformation optics at the nanoscale using polaritons in a wide range of freestanding complex oxide membranes.

Ferroelectric Switching in Hybrid Molecular Beam Epitaxy-Grown BaTiO3 Films

ArXiv.org · 2025-05-03

Molecular beam epitaxy (MBE) is a promising synthesis technique for both heterostructure growth and epitaxial integration of ferroelectric BaTiO3. However, a direct measurement of the remnant polarization (P_r) has not been previously reported in MBE-grown BaTiO3 films. We report the in-situ growth of an all-epitaxial SrRuO3/BaTiO3/SrRuO3 heterostructure on Nb-doped SrTiO3 (001) substrates by hybrid MBE using metal-organic precursors. This capacitor structure consisting of 16 nm SrRuO3/40 nm BaTiO3/16 nm SrRuO3 shows hysteretic polarization-electric field (P-E) curves with P_r = 15 μC cm-2 at frequencies ranging from 500 Hz to 20 kHz, after isolating the intrinsic ferroelectric response from non-ferroelectric contributions using the Positive-Up-Negative-Down (PUND) method. We hypothesize that the asymmetry in switching behavior and current leakage has origins in structural defects.

WS2 p-MOSFETs with channels deposited by plasma-enhanced atomic-layer deposition

Applied Physics Letters · 2025-06-23

We report the demonstration of p-channel WS2 metal oxide field effect transistors (MOSFETs) using channels deposited by plasma-enhanced atomic layer deposition (PE-ALD). Substrate-gated devices using PE-ALD WS2 films deposited at 300 °C were fabricated with source-to-drain spacing, LDS, ranging from 0.1 to 1.1 µm. Despite being undoped, both 3.4-nm and 2.1-nm-thick films displayed p-type conduction. Substrate-gated devices with LDS = 0.1 µm had on-state current, Ion, of 0.86 µA/µm (0.40 µA/µm) at a drain voltage of VD = −1 V for a channel thickness of 3.4 nm (2.1 nm). It was found that the thinner films displayed improved on/off current ratio, Ion/Ioff, and MOSFETs with 2.1-nm-thick channels had Ion/Ioff = 16.7 compared to only 6.8 for 3.4-nm-thick channels. Devices with 1.4-nm-thick WS2 channels were also fabricated by incorporating a 1.6-nm capping layer of NbxW1−xSy, where NbxW1−xSy provided a heavily doped layer underneath the metal contact and was oxidized in the region between source and drain contacts using low-temperature O2 annealing. These devices had Ion/Ioff as high as 28 at room temperature, a substantial improvement to the WS2-only devices. Measurement at 77 K showed Ion/Ioff values as high as 260, and extraction of the contact barrier height using temperature-dependent measurements showed that a small energy barrier still exists between the NbxW1−xSy and the WS2.

Theoretical Optimal Specifications of Memcapacitors for Charge-Based In-Memory Computing

2025-01-20

This paper presents the optimal theoretical specifications of memcapacitors that allow them to surpass the existing state-of-the-art in-memory computing (IMC) prototypes in terms of energy efficiency and weight density. To do so, we build and simulate the SPICE model of an existing memcapacitor device in an IMC macro featuring charge-based computing. We develop the energy efficiency model and weight density model of the memcapacitor-based IMC macro, which are verified against SPICE simulation. Finally, we present the optimal theoretical specifications for memcapacitor devices to obtain a 10x improvement in energy efficiency and/or weight density over the existing IMC prototypes.

Generalized Energy Band Alignment Model for van der Waals Heterostructures with a Charge Spillage Dipole

ACS Nano · 2025-10-22

∼ 0.9 across type-I, -II, and -III stacks. Machine learning feature analysis confirms that these two descriptors dominate the underlying physics, indicating that the model is near-minimal and broadly transferable. The gLR framework therefore provides both mechanistic insight and a fast and accurate surrogate for high-throughput screening of the vast vdW heterostructure design space.

Interfacial strong coupling and negative dispersion of propagating polaritons in freestanding oxide membranes

ArXiv.org · 2025-03-03

Membranes of complex oxides like perovskite SrTiO3 extend the multi-functional promise of oxide electronics into the nanoscale regime of two-dimensional materials. Here we demonstrate that free-standing oxide membranes supply a reconfigurable platform for nano-photonics based on propagating surface phonon polaritons. We apply infrared near-field imaging and -spectroscopy enabled by a tunable ultrafast laser to study pristine nano-thick SrTiO3 membranes prepared by hybrid molecular beam epitaxy. As predicted by coupled mode theory, we find that strong coupling of interfacial polaritons realizes symmetric and antisymmetric hybridized modes with simultaneously tunable negative and positive group velocities. By resolving reflection of these propagating modes from membrane edges, defects, and substrate structures, we quantify their dispersion with position-resolved nano-spectroscopy. Remarkably, we find polariton negative dispersion is both robust and tunable through choice of membrane dielectric environment and thickness and propose a novel design for in-plane Veselago lensing harnessing this control. Our work lays the foundation for tunable transformation optics at the nanoscale using polaritons in a wide range of freestanding complex oxide membranes.