Shiyou Chen

Deep-level transient spectroscopy (DLTS) is a key experimental method for defect characterization, yet its analysis remains controversial, and the two widely used models developed by Henry and Lang are conflicting. We show that the Henry–Lang model is valid only under the Condon approximation, as well as high-temperature and strong electron–phonon coupling approximations, which cause incorrect temperature dependence of carrier emission and capture. Here we develop a rigorous nonradiative multiphonon (NMP) model and demonstrate that the temperature dependence is governed predominantly by effective phonons with large phonon wavefunction overlap and high thermal occupation. The effective phonons are strongly correlated with lattice relaxation. The neglect of this correlation in existing DLTS models introduces substantial errors when they are used to fit DLTS-measured emission rates. Our comparison for 24 different defects in 12 semiconductors, including Si, SiC, and Ga2O3, shows that the Henry–Lang model gives a completely different temperature dependence of carrier capture cross section from that obtained using the rigorous NMP model, with errors reaching up to six orders of magnitude at room temperature. Our study highlights the necessity of revisiting previous DLTS analysis studies using the rigorous NMP model.

ML potentials and MD simulations reveal t -like DWs dominate polarization switching in HfO ₂ .

The integration of two‐dimensional (2D) semiconductors into large‐scale digital circuits demands precise, localized, and damage‐free doping to achieve threshold voltage ( V _TH ) matching—a critical challenge for existing technologies. Here, we present a non‑destructive and precisely controllable n‑type doping strategy based on low‑work‑function aluminum (Al) nanoclusters. By depositing ultrathin, spatially discrete Al nanoclusters onto the 2D channel, we exploit efficient vertical electron injection while fundamentally preventing channel shorting. This approach enables precise and continuous V _TH modulation without compromising lattice integrity. Using MoS ₂ as a model system, we demonstrate top‐gate transistors with widely tunable V _TH and exceptional device‐to‐device uniformity. Leveraging this highly controllable doping scheme, we successfully fabricated high‐performance enhancement‐depletion (E‐D) inverters exhibiting full logic swings and robust noise margins. We further realized complex digital building blocks, including logic gates (NAND, NOR, XOR), a one‐bit full adder, and a five‐stage ring oscillator (18.25 kHz), collectively confirming that overall process variation is strictly controlled across multiple cascading stages. Furthermore, the general applicability of this vertical injection mechanism is validated on p‐type MoTe ₂ . By integrating physical mechanism analysis, device‐level optimization, and system‐level demonstrations, this work establishes a process‐compatible, localized doping methodology, providing a critical pathway toward next‐generation high‐density 2D integrated circuits.

Floating-gate memory, as one of the most widely used nonvolatile memories for practical deployments, plays a significant role in modern electronics. However, its inherent speed limitations make it challenging to keep pace with the explosive growth of data generation and the evolving demands of innovative hardware applications. Herein, we demonstrate an ultrafast floating-gate memory based on a two-dimensional (2D) MoS2/h-BN/graphene/CuInP2S6 heterostructured device. Comprehensive experimental investigations and technology computer-aided design (TCAD) simulations reveal that the matched ferroelectric polarization field of CuInP2S6 enhances the electric field across the tunneling layer, thereby effectively facilitating Fowler–Nordheim tunneling. This enables program/erase speeds as low as 13 ns, a performance competitive with that of dynamic random access memory (DRAM) that boasts high operational speeds but suffers from volatility. Our findings demonstrate the enormous potential of ferroelectric-enhanced floating-gate memory for next-generation high-speed nonvolatile memory and cutting-edge hardware applications.

The formation energy of charged defects is a key quantity for assessing dopability and electronic properties of various semiconductor materials, but its evaluation using density functional theory (DFT) is computationally demanding for large‐scale systems. Although machine‐learning models have been introduced to accelerate charged‐defect calculations, limited size transferability when trained only on small defect supercells leads to substantial training costs, and charged‐defect corrections remain a nontrivial challenge. Here, we introduce a machine‐learning Hamiltonian (MLH) model–based method that extends the model's size transferability of electronic structures to charged‐defect formation energies and enables accurate charged‐defect corrections through reliable electrostatic potentials in large supercells. Using oxygen vacancies in SiO ₂ and nitrogen vacancies in GaN as benchmarks, a model trained on defect structures with at most 95 atoms accurately predicts formation energies in supercells larger than 400 atoms, with errors below 0.07 eV for neutral defects and below 0.3 eV for +1 and +2 charge states. These results demonstrate the feasibility of extending our approach to more complex defect systems.

Wurtzite Al _1-x Sc _x N ferroelectrics exhibit exceptional polarization and thermal stability, making them highly promising for a wide range of electronic applications. However, a more profound understanding is required regarding the atomic-scale mechanism through which cation substitution lowers the switching energy barrier and thus reduces the coercive field. We used spherical aberration–corrected transmission electron microscopy to reveal a periodic modulation of cation-anion spacing along the polarization direction, forming alternating atomic dipole layers. This modulation arises from energetically favorable chemical ordering of aluminum and scandium atoms between adjacent layers, with layer-resolved asymmetry in atomic arrangement. In situ imaging directly captures atomic-scale, noncollective, stepwise polarization switching, revealing intermediate states and local spacing fluctuations. Compositional inhomogeneity in these dipole layers creates multiple transient states that reduce the switching energy barrier. Our findings connect atomic-scale dipole structures to polarization switching kinetics, enabling the rational design of wurtzite ferroelectrics.

Charge trapping in gate dielectrics governs reliability degradation in advanced transistors, and an essential mission is calculating the trapping rates of different defects accurately. Here, by high-throughput ab initio calculations, we demonstrate a significant asymmetric relaxation behavior of oxide defects during charge trapping and emission, and thus the predominantly assumed symmetric relaxation is invalid. Multiscale atomic-to-device simulations further reveal that the conventional symmetric approximation introduces orders-of-magnitude errors in charge transfer rates and qualitatively mischaracterizes the defect-resolved degradation. Therefore, we provide asymmetric relaxation data and corresponding modified charge trapping model for accurate reliability simulation of advanced transistors.

Previous femtosecond pump-terahertz probe experiments revealed that the intrinsically coupled insulator-to-metal (IMT) and structural phase (SPT) transitions in niobium dioxide (NbO₂) occur at two distinct fluence thresholds, exhibiting a novel dual-threshold feature. Here, we demonstrate that they are induced by two distinct types of electron-phonon interactions, different from the earlier interpretation of purely electronic IMT at the first fluence threshold (F_th1) and photothermal SPT at the second (F_th2). At F_th1, the photoexcited holes are self-trapped at specific niobium sites, assisted by thermal phonons. Such polaronic distortions drive the IMT into a bad metallic phase, beyond purely electronic effects. At F_th2, besides the IMT that occurs first, coherent phonons induce SPT from the zigzag Nb chains to linear isometric configurations, which enhances the metallicity via a nonthermal pathway rather than thermal effects. Our study provides theoretical insights into potential applications of NbO₂ for multilevel and energy-efficient storage.

Platinum (Pt) is widely used for carrier-lifetime control in silicon power devices, yet the microscopic nonradiative recombination mechanism of the substitutional platinum (Pt_Si) dopant remains debated. Using first-principles calculations combined with nonradiative multiphonon theory, we systematically investigate the electronic structures and carrier capture dynamics of Pt_Si. Our results show that both the donor (+/0) and acceptor (0/-) levels of Pt_Si exhibit large capture cross sections for electron and hole carriers, thereby making Pt_Si an effective recombination center. Notably, the calculated capture cross sections are sensitive to the symmetry-equivalent defect configurations with different Jahn-Teller distortions. By properly accounting for two different D_2d configurations of neutral Pt_Si during transitions, our calculated carrier capture cross sections align well with experimental values. This work provides a microscopic picture of the carrier capture processes induced by Pt_Si and emphasizes the importance of symmetry-equivalent configurations in defect-assisted nonradiative recombination.