arXiv subjects

Zekun Hu

Publications and source records attributed to Zekun Hu.

8 recordsLinked to original sources

arXiv2026

Compositional gradient engineering for enhanced ferroelectricity in ultrathin AlScN

Ferroelectric AlScN is promising for CMOS-compatible non-volatile memory, but thickness scaling is limited by leakage, premature breakdown, and defect-mediated failure. Here we show that compositional grading within a continuous wurtzite AlN-AlScN lattice mitigates these limitations by distributing structural and polarization discontinuities across the film thickness, reducing defect formation and local field concentration. In a 20 nm graded heterostructure, monotonic Sc incorporation and AlN-rich boundaries produce reversible ferroelectric switching, an as-grown metal-polar state, a 21% higher breakdown field, 10% enhanced remanent polarization, and 40x higher resistivity relative to homogeneous AlScN. Time-domain PUND measurements reveal strongly suppressed post-switching leakage, consistent with reduced defect-assisted and polarization-coupled conduction. This improved dielectric robustness enables ferroelectric functionality in 5 nm graded stacks containing only a 2 nm $\mathrm{Al}_{0.64}\mathrm{Sc}_{0.36}\mathrm{N}$ region, with measurable switching near 1 V. These results establish compositional grading as a defect- and field-management strategy for scalable ultrathin wurtzite ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2026

Controlled non-volatile modulation of optical dispersion in monolayer tungsten disulfide via ferroelectric polarization patterning

The manipulation of optical properties, including reflection, refraction, polarization, phase, and frequency, has long been central to advancing photonic and optoelectronic technologies. However, existing electro-optical approaches rely on volatile mechanisms that require continuous power consumption. Here, we demonstrate strong, nonvolatile modulation of optical dispersion in monolayer tungsten disulfide (ML WS2) using patterned ferroelectric domains in aluminum scandium nitride (AlScN). By locally poling ferroelectric domains into opposite states, we achieve substantial manipulation of the complex refractive index (Delta n > 0.7, Delta k > 0.4) and excitonic energy shifts (~50 meV) in ML WS2, comparable to previous gate-tuning approaches while eliminating continuous power consumption. We introduce an asymmetric screening model that reveals how ferroelectric polarization induces carrier-density-dependent Coulomb screening, leading to distinct excitonic behaviors between electron- and hole-doped regions. Furthermore, we demonstrate a gate-free lateral p-n homojunction with a rectification ratio of 6e10^3, formed through spatial carrier redistribution. These findings establish ferroelectric/2D heterostructures as a powerful platform for nonvolatile optical dispersion engineering, enabling energy-efficient, reconfigurable photonic and optoelectronic devices.

physics.optics↗

arXiv2025

Demonstration of highly scaled AlScN ferroelectric diode memory with storage density > 100 Mbit/mm$^2$

Wurtzite nitride ferroelectric materials have emerged as promising candidates for next-generation memory applications due to their exceptional polarization properties and compatibility with conventional semiconductor processing techniques. Here, we demonstrate the first successful areal scaling of Aluminum Scandium Nitride (AlScN) ferroelectric diode (FeDiode) memory down to 40 nm device diameters while maintaining ON/OFF > 60. Using a 20 nm thick Al0.64Sc0.36N ferroelectric layer, we evaluate both metal-insulator-ferroelectric-metal (MIFM) and metal-ferroelectric-metal (MFM) architectures for scaled resistive memory devices. Our scaled devices exhibit an enhanced breakdown-to-coercive field ratio exceeding 2.6 due to increased breakdown field. The MIFM devices demonstrate stable 3-bit non-volatile multistate behavior with clearly distinguishable resistance states and retention exceeding 4*10^4 seconds at 85 C. By achieving more than a million-fold areal scaling with enhanced performance metrics, this work establishes AlScN-based FeDiode memory as a highly promising platform for non-volatile storage with potential for direct integration into CMOS technology.

cond-mat.mes-hall↗

arXiv2025

Observation of giant remnant polarization in ultrathin AlScN at cryogenic temperatures

The discovery of wurtzite ferroelectrics opens new frontiers in polar materials, yet their behavior at cryogenic temperatures remains unexplored. Here, we reveal unprecedented ferroelectric properties in ultrathin (10 nm) Al$_{0.68}$Sc$_{0.32}$N (AlScN) at cryogenic temperatures where the properties are fundamentally distinct from those of conventional oxide ferroelectrics. At 12 K, we demonstrate a giant remnant polarization exceeding 250 $\mu$C/cm$^2$ -- more than twice that of any known ferroelectric -- driven by an enhanced c/a ratio in the wurtzite structure. Our devices sustain remarkably high electric fields (~13 MV/cm) while maintaining reliable switching, achieving over 104 polarization reversal cycles at 12 K. Critically, this breakdown field strength approaches that of passive dielectric materials while maintaining ferroelectric functionality. The extraordinary polarization enhancement and high-field stability at cryogenic temperatures contrasts sharply with oxide ferroelectrics, establishing wurtzite ferroelectrics as a distinct class of polar materials with implications spanning fundamental physics to cryogenic non-volatile memory and quantum technologies.

cond-mat.mtrl-sci↗

arXiv2024

Al0.68Sc0.32N/SiC based metal-ferroelectric-semiconductor capacitors operating up to 1000 {\deg}C

Ferroelectric (Fe) materials-based devices show great promise for non-volatile memory applications, yet few demonstrate reliable operation at elevated temperatures. In this work, we demonstrate Ni/Al0.68Sc0.32N/4H-SiC metal-ferroelectric-semiconductor capacitors for high-temperature non-volatile memory applications. Our 30-nm thick ferroelectric Al0.68Sc0.32N film grown on SiC exhibits stable and robust ferroelectric switching up to 1000{\deg}C. The coercive field decreases linearly from -6.4/+11.9 MV cm-1 at room temperature to -3.1/+7.8 MV cm-1 at 800{\deg}C, further reducing to -2.5 MV cm-1 at 1000{\deg}C. At 600{\deg}C, the devices achieve remarkable reliability with ~2000 endurance cycles and over at least 100 hours of retention with negligible polarization loss. At 800{\deg}C, the devices retain data for at least 10,000 seconds and exceed 400 write cycles. Our results further highlight the potential for ferroelectric AlScN thin-films particularly when paired with SiC semiconductor substrates for high-temperature non-volatile memory.

cond-mat.mtrl-sci↗

arXiv2024

Broadband Light Harvesting from Scalable Two-Dimensional Semiconductor Heterostructures

Broadband absorption in the visible spectrum is essential in optoelectronic applications that involve power conversion such as photovoltaics and photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic structures that maximize absorption using surface plasmons and/or Fabry-Perot cavities, which limits the weight efficiency of the device. Here, we show the theoretical and experimental realization of an unpatterned/planar semiconductor thin-film absorber based on monolayer transition metal dichalcogenides (TMDCs). We experimentally demonstrate an average total absorption in the visible range (450 nm - 700 nm) of > 70% using > 4 nm of semiconductor absorbing materials scalable over large areas with vapor phase growth techniques. Our analysis suggests that a power conversion efficiency (PCE) of 15.54% and a specific power > 300 W g^-1 may be achieved in a photovoltaic cell based on this metamaterial absorber.

physics.optics↗

arXiv2024

Tandem Photovoltaics from 2D Transition Metal Dichalcogenides on Silicon

The demand for high-efficiency photovoltaic systems necessitates innovations that transcend the efficiency limitations of single-junction solar cells. This study investigates a tandem photovoltaic architecture comprising a top-cell with a transition metal dichalcogenide (TMDC) superlattice absorber and a bottom-cell of crystalline silicon (c-Si), focusing on optimizing the light absorption and electrical performance of the combined structure. Through the transfer matrix method and electrical simulations, we optimized the geometry of the superlattice, determining that a siz-layer MoSe2 configuration with a 40 nm SiO2 antireflective layer maximizes photon absorption while mitigating additional weight and preserving the cell's structural integrity. The results show that the optimized TMDC superlattice significantly improves the PCE of the tandem design to 28.96%, and increase of 5.68% over the original single-junction c-Si solar cell's efficiency. This advancement illustrates the potential of TMDC material in next-generation solar cells and presents a promising avenue for the development of highly efficient, tandem photovoltaic systems via van der Waals integration of the top cell on c-Si

physics.optics↗

arXiv2023

How Good Can 2D Excitonic Solar Cells Be?

Excitonic semiconductors have been a subject of research for photovoltaic applications for many decades. Among them, the organic polymers and small molecules based solar cells have now exceeded 19% power conversion efficiency (PCE). While organic photovoltaics (OPVs) are approaching maturity, the advent of strongly excitonic inorganic semiconductors such as two-dimensional transition metal dichalcogenides (TMDCs) has renewed interest in excitonic solar cells due to their high-optical constants, stable inorganic structure and sub-nm film thicknesses. While several reports have been published on TMDC based PVs, achieving power conversion efficiencies higher than 6% under one-sun AM1.5G illumination has remained challenging. Here, we perform a full optical and electronic analysis of design, structure and performance of monolayer TMDC based, single-junction excitonic PVs. Our computational model with optimized properties predicts a PCE of 9.22% in a superlattice device structure. Our analysis suggests that, while the PCE for 2D excitonic solar cells may be limited to < 10%, a specific power > 100 W g-1 may be achieved with our proposed designs, making them attractive in aerospace, distributed remote sensing, and wearable electronics.

physics.app-ph↗