Search

Aluminum (Al) ion implantation is one of the most important technologies in SiC device manufacturing processes due to its ability to produce the p-type doping effect, which is essential to building p–n junctions and blocking high voltages. However, besides the doping effect, defects are also probably induced by the implantation. Here, the impacts of Al ion implantation-induced defects on 4H-SiC MOSFET channel transport behaviors are studied using a multiscale simulation flow, including the molecular dynamics (MD) simulation, density functional theory (DFT) calculation, and tight-binding (TB) model-based quantum transport simulation. The simulation results show that an Al ion can not only replace a Si lattice site to realize the p-doping effect, but it can also replace the C lattice site to induce mid-gap trap levels or become an interstitial to induce the n-doping effect. Moreover, the implantation tends to bring additional point defects to the 4H-SiC body region near the Al ions, which will lead to more complicated coupling effects between them, such as degrading the p-type doping effect by trapping free hole carriers and inducing new trap states at the 4H-SiC bandgap. The quantum transport simulations indicate that these coupling effects will impede local electron transports, compensating for the doping effect and increasing the leakage current of the 4H-SiC MOSFET. In this study, the complicated coupling effects between the implanted Al ions and the implantation-induced point defects are revealed, which provides new references for experiments to increase the accepter activation rate and restrain the defect effect in SiC devices. [ABSTRACT FROM AUTHOR]

Transition‐metal‐ion doping is an effective method to shorten bandgap and enhance visible‐light absorption of TiO2, but there are still some serious challenges for most doping technologies, such as nonuniform doping, severe lattice damages, metal atoms agglomeration, and inactivated impurities. Herein, a simple and universal hydrothermal method is developed to realize the effective transition‐metal ions doping of TiO2 (including Fe, Co, Mn, Cu, V, and Cr). The photoelectrochemical water splitting performances of Cr‐doped TiO2 nanorods with multifarious Cr ion valence states (Cr3+ or Cr6+ ions), various Cr‐ion concentrations, with or without oxygen vacancy activation are emphatically and systematically studied. Experiments and theoretical calculations demonstrate that the remarkably enhanced carrier separation and injection efficiencies are the key factors to improve the visible‐light photoactivity, benefiting from the homogeneous distribution of impurity atoms and the incorporation of oxygen vacancies. The Cr3+‐ion‐doped TiO2 nanorod arrays with oxygen vacancy activation (Cr3+/Ov–TiO2) displays an impressive incident photon‐to‐electron conversion efficiency of 5.4% at 450 nm visible light, far superior to the pure TiO2 of 0.03%. Furthermore, no obvious photocurrent decay is observed in the Cr3+/Ov–TiO2 photoanode after 12 h continuous light illumination. [ABSTRACT FROM AUTHOR]

Magnetic topological insulators MnBi2Te4 and Bi2Te3/MnBi2Te4 have attracted extensive attention because of their novel physical properties and promising application potentials. In this work, based on the dataset from density functional calculations, a deep neural network potential is trained to study the thermal transport properties of MnBi2Te4 and Bi2Te3/MnBi2Te4. The thermal conductivity of MnBi2Te4 is first calculated using equilibrium molecular dynamics combined with this potential, and the results are in good agreement with the experimental values. The thermal conductivity of Bi2Te3/MnBi2Te4 is then predicted using the same approach. Compared with that of MnBi2Te4, the in-plane thermal conductivity of Bi2Te3/MnBi2Te4 does not change significantly, but the out-of-plane one is much lower. The low out-of-plane thermal conductivity of Bi2Te3/MnBi2Te4 is extremely desirable for high thermoelectric performance. By investigation of the corresponding phonon dispersion relations, it is found that the band gaps at the boundary of the Brillouin zone and the inhibition of phonon velocity lead to the large reduction of out-of-plane thermal conductivity in Bi2Te3/MnBi2Te4. [ABSTRACT FROM AUTHOR]

The deficient catalytic activity of nanozymes and insufficient endogenous H2O2 in the tumor microenvironment (TME) are major obstacles for nanozyme‐mediated catalytic tumor therapy. Since electron transfer is the basic essence of catalysis‐mediated redox reactions, we explored the contributing factors of enzymatic activity based on positive and negative charges, which are experimentally and theoretically demonstrated to enhance the peroxidase (POD)‐like activity of a MoS2 nanozyme. Hence, an acidic tumor microenvironment‐responsive and ultrasound‐mediated cascade nanocatalyst (BTO/MoS2@CA) is presented that is made from few‐layer MoS2 nanosheets grown on the surface of piezoelectric tetragonal barium titanate (T‐BTO) and modified with pH‐responsive cinnamaldehyde (CA). The integration of pH‐responsive CA‐mediated H2O2 self‐supply, ultrasound‐mediated charge‐enhanced enzymatic activity, and glutathione (GSH) depletion enables out‐of‐balance redox homeostasis, leading to effective tumor ferroptosis with minimal side effects. [ABSTRACT FROM AUTHOR]

A single device with switchable functions is highly attractive to the growing demands of complex optoelectronics. However, most of the currently reported devices either exhibit a lack of multifunction operation or require complex electrode configurations with limited performances. Here, a new concept of a functionalized‐black phosphorus (f‐BP)/MoS2 heterojunction is proposed, which enables the coexistence of an optoelectronic memory and a detector in a single device. The oxidation‐induced artificial‐traps on the BP surface result in a gate‐modulated photogating effect, so that the device can be freely switched between memory and detector by simply changing the back‐gate voltage. In the memory model, the device has an ultra‐long storage time (10 years), an ultra‐high on/off ratio (3.5 × 107), and outstanding multi‐bit storage (≈90 states), while in the detector model, the device still exhibits a fast response (130/260 µs), an impressive responsivity (22.2 A W−1), and self‐driven broadband detection (ultraviolet to near‐infrared). Most importantly, the highly anisotropic BP enables fast NIR polarization resolution with a maximum polarization ratio of 6.98 at 1064 nm. [ABSTRACT FROM AUTHOR]

Artificially stacked van der Waals heterostructures (vdWH) of two-dimensional (2D) atomic layers have attracted considerable attention due to substantial interactions between different layers. In particular, the strongly bound interlayer exciton (IX) within vdWH offers a platform for exploring fundamental physics as well as innovative device applications. However, to date, it remains a critical challenge to modulate the IX emission energy, limiting the achievement of high-performance spin-valleytronics and excitonic devices. Here, we report a simple strain engineering approach to efficiently modulate the MoS2/WSe2 IX via uniaxial strain. By encapsulating the vdWH within a flexible substrate, the applied mechanical strain could be effectively transferred to the lattice of vdWH during the mechanical bending process, leading to an unprecedent IX modulation range of 144 meV with a linear fitted gauge factor of 121.8 meV per 1% strain. Furthermore, we found that the gauge factor of IX in vdWH is larger than that of individual MoS2 and WSe2 intralayer excitons, further confirming that the observed IX originates from the momentum-indirect exciton between the K point of the MoS2 conduction band and the Γ point of the WSe2 valence band. Our study not only achieves a high vdWH IX modulation value using efficient strain engineering but also provides a route to investigate the evolution of band energy for various two-dimensional (2D) materials as well as their vertical vdWH. [ABSTRACT FROM AUTHOR]

Although the irreplaceable position of silicon (Si) semiconductor materials in the field of information has become a consensus, new materials continue to be sought to expand the application range of semiconductor devices. Among them, research on wide bandgap semiconductors has already achieved preliminary success, and the relevant achievements have been applied in the fields of energy conversion, display, and storage. However, similar to the history of Si, the immature material grown and device manufacturing processes at the current stage seriously hinder the popularization of wide bandgap semiconductor-based applications, and one of the crucial issues behind this is the defect problem. Here, we take amorphous indium gallium zinc oxide (a-IGZO) and 4H silicon carbide (4H-SiC) as two representatives to discuss physical/mechanical properties, electrical performance, and stability from the perspective of defects. Relevant experimental and theoretical works on defect formation, evolution, and annihilation are summarized, and the impacts on carrier transport behaviors are highlighted. State-of-the-art applications using the two materials are also briefly reviewed. This review aims to assist researchers in elucidating the complex impacts of defects on electrical behaviors of wide bandgap semiconductors, enabling them to make judgments on potential defect issues that may arise in their own processes. It aims to contribute to the effort of using various post-treatment methods to control defect behaviors and achieve the desired material and device performance.

Ferroelectric two-dimensional (2D) materials with a high transition temperature are highly desirable for new physics and next-generation memory electronics. However, the long-range polar order of ferroelectrics will barely persist when the thickness reaches the nanoscale. In this work, we synthesized 2D CuCrS 2 nanosheets with thicknesses down to one unit cell via van der Waals epitaxy in a chemical vapor deposition system. A combination of transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements confirms the R 3 m space group and noncentrosymmetric structure. Switchable ferroelectric domains and obvious ferroelectric hysteresis loops were created and visualized by piezoresponse force microscopy. Theoretical calculation helps us understand the mechanism of ferroelectric switching in CuCrS 2 nanosheets. Finally, we fabricated a ferroelectric memory device that achieves an on/off ratio of ∼10 2 and remains stable after 2000 s, indicating its applicability in novel nanoelectronics. Overall, 2D CuCrS 2 nanosheets exhibit excellent ferroelectric properties at the nanoscale, showing great promise for next-generation devices.

The emerging Ruddlesden-Popper two-dimensional perovskite (2D PVK) has recently joined the family of 2D semiconductors as a potential competitor for building van der Waals (vdW) heterostructures in future optoelectronics. However, to date, most of the reported heterostructures based on 2D PVKs suffer from poor spectral response that is caused by intrinsic wide bandgap of constituting materials. Herein, a direct heterointerface bandgap (∼0.4 eV) between 2D PVK and ReS 2 is demonstrated. The strong interlayer coupling reduces the energy interval at the heterojunction region so that the heterostructure shows high sensitivity with the spectral response expanding to 2000 nm. The large type-II band offsets exceeding 1.1 eV ensure fast photogenerated carriers separation at the heterointerface. When this heterostructure is used as a self-driven photodetector, it exhibits a record high detectivity up to 1.8 × 10 14 Jones, surpassing any reported 2D self-driven devices, and an impressive external quantum efficiency of 68%.

Regulation of cellular oxidative stress plays a critical role in revealing the molecular mechanisms of cellular activities and thus is a potential strategy for tumor treatment. Optical methods have been employed for intelligent regulation of oxidative stress in tumor regions. However, long-time continuous irradiation inevitably causes damage to normal tissues. Herein, a ferrocene-containing nucleic acid-based energy-storage nanoagent was designed to achieve the continuous photo-regulation of cellular oxidative stress in the dark. Specifically, the photoenergy stored in the agent could convert effectively and accelerate Fenton-like reaction continuously, augmenting cellular oxidative stress. This nanoagent could also silence oxidative damage repair genes to further amplify oxidative stress. This strategy not only provides oxidative stress regulation for studying the molecular mechanisms of biological activities, but also offers a promising step toward tumor microenvironment modulation., (© 2022 Wiley-VCH GmbH.)

Nonvolatile optoelectronic memories based on organic-inorganic hybrid perovskites have appeared as powerful candidates for next-generation soft electronics. Here, ambipolar SnO transistor-based nonvolatile memories with multibit memory behavior (11 storage states, 120 nC state -1 ) and ultralong retention time (>10 5 s) are demonstrated for which an Al 2 O 3 /two-dimensional Ruddlesden-Popper perovskite (2D PVK) heterostructure dielectric architecture is employed. The unique storage features are attributed to suppressed gate leakage by Al 2 O 3 layer and hopping-like ionic transport in 2D PVK with varying activation energy under different light intensities. The photoinduced field-effect mechanism enables top-gated transistor operation under illumination, which would not be achieved under dark. As a result, the device exhibits remarkable photoresponsive characteristics, including ultrahigh specific detectivity (2.7 × 10 15 Jones) and broadband spectrum distinction capacity (375-1064 nm). This study offers valuable insight on the PVK-based dielectric engineering for information storage and paves the way toward multilevel broadband-response optoelectronic memories.