Carrier imbalance—characterized by an electron rich active region caused by limited hole injection—has long been a major challenge for AlGaN-based UV-A laser diodes, severely degrading their optoelectronic performance. In this work, we investigate AlGaN-based UV-A laser diodes emitting at approximately 358 nm and propose a hybrid design that combines a thin-well p-AlGaN/GaN superlattice hole-injection layer with a compositionally graded AlGaN electron-blocking layer (EBL) to simultaneously enhance hole injection and suppress electron leakage, thereby restoring electron-hole injection balance and improving carrier transport. Numerical simulations demonstrate that the superlattice markedly reduces the polarization-induced electric field near the EBL, alleviating interfacial carrier accumulation and boosting the local hole concentration in the p type region by more than two orders of magnitude. Moreover, the graded EBL provides improved barrier modulation, suppressing electron leakage while facilitating hole injection, thereby enhancing the radiative recombination rate. Compared with the conventional structure with fixed compositions, the output optical power increases by 240%, and the wall-plug efficiency increases by 386.2%. These results suggest a promising strategy for achieving highly efficient hole injection in AlGaN-based UV-A laser diodes.

Precise signal identification in solar-blind deep-ultraviolet (DUV) detection critically relies on high-performance devices with exceptional spectral selectivity. A novel strategy is proposed to significantly enhance DUV photodetector performance by integrating plasmonic nanohole engineering with ultrashort-period AlN/GaN superlattices for ultranarrow-band detection. Simulations indicate that Al-filled nanoholes with a diameter of 230 nm and a sidewall angle of 60 degrees can yield up to a 31-fold enhancement of the localized electric field at the Al-nanohole sidewall interfaces compared to nanohole structures without Al. Accordingly, metal-semiconductor-metal (MSM) photodetectors incorporating Al-filled hexagonal nanohole arrays within the AlN/GaN superlattice absorption layers were fabricated. The designed three-dimensional architecture, which provides an increased interaction area and effective optical path length, achieves a remarkable peak responsivity of 42.6 mA/W at 238 nm under a 15 V bias. This represents a 4.5-fold improvement over planar reference devices. Furthermore, the devices exhibit ultranarrow spectral selectivity with a full-width at half-maximum (fwhm) of only 19 nm, attributed to the precise spectral alignment between the localized surface plasmon resonance (LSPR) and the superlattice absorption profile. This novel combination of plasmonics and nanohole superlattices offers a promising avenue for high-performance DUV photodetectors in applications requiring highly selective spectral operation.

ABSTRACT Ferromagnetic van der Waals (vdW) heterostructures are pivotal for next‐generation spintronics, especially in realizing novel functionalities like antisymmetric magnetoresistance (ASMR). While ASMR holds immense potential for multi‐state memory and logic operations, achieving stable performance across a broad range of conditions and realizing diverse multi‐state functionalities remain key challenges. Here, we report the demonstration of multi‐state ASMR signals in a Fe 3 GaTe 2 /InSe/Fe 3 GaTe 2 vdW heterostructure, effectively operating up to 320 K. Intriguingly, the conventional three‐state ASMR undergoes a unique temperature‐induced shape reversal, which is precisely correlated with the temperature‐dependent crossover of the coercive fields of the two Fe 3 GaTe 2 layers. Through adapted measurement configurations, an unconventional four‐state ASMR, featuring distinct high, intermediate‐1, intermediate‐2, and low resistance states, has been obtained, holding significant promise for enhancing multi‐state memory density. Crucially, the device exhibits superior signal stability across wide variations in bias current (0.01–100 µA ) and magnetic field angle (0 ° –360 ° ). Programmable prototype devices demonstrating highly distinguishable states are also presented. The junction resistance of our devices is only a few kiloohms owing to the perfect Fermi level alignment between Fe 3 GaTe 2 and InSe, making them highly compatible with complementary metal–oxide–semiconductor circuits. This work lays a solid foundation for future stable multi‐state memory applications.

Efficient and reliable spin injection at room temperature with scalability is crucial for spintronic applications but remains challenging. Direct ferromagnetic metal deposition on two-dimensional materials often leads to inefficient transparent contacts. Here, we introduce an indium buffer layer between ferromagnetic cobalt (Co) and graphene to establish high-efficiency van der Waals (vdW) tunnel contacts. This buffer layer facilitates a physisorption interface between Co and graphene with a well-defined vdW gap, which functions as an effective spin tunnel barrier. Through buffer layer thickness optimization, we achieved a room-temperature spin injection efficiency of approximately 25% in graphene, comparable to the best single-crystalline oxide-tunnel-barrier-based devices, alongside explicit nonlocal spin valve signals and Hanle spin precession. We further demonstrate the scalability of our approach through uniform performance across multi-channel graphene spin valves and its versatility by achieving efficient spin injection in semiconducting MoS2 with an average efficiency of about 19.7%. Our strategy offers a simple, cost-efficient, and industry-compatible method for future large-scale and efficient spintronic applications.

Ferromagnetic van der Waals (vdW) heterostructures are pivotal for next-generation spintronics, especially in realizing novel functionalities like antisymmetric magnetoresistance (ASMR). While ASMR holds immense potential for multi-state memory and logic operations, achieving stable performance across a broad range of conditions and realizing diverse multi-state functionalities remain key challenges. Here, we report the demonstration of multi-state ASMR signals in a Fe3GaTe2/InSe/Fe3GaTe2 vdW heterostructure, effectively operating up to 320 K. Intriguingly, the conventional three-state ASMR undergoes a unique temperature-induced shape reversal, which is precisely correlated with the temperature-dependent crossover of the coercive fields of the two Fe3GaTe2 layers. Through adapted measurement configurations, an unconventional four-state ASMR, featuring distinct high, intermediate-1, intermediate-2, and low resistance states, has been obtained, holding significant promise for enhancing multi-state memory density. Crucially, the device exhibits superior signal stability across wide variations in bias current (0.01-100 µA) and magnetic field angle (0°-360°). Programmable prototype devices demonstrating highly distinguishable states are also presented. The junction resistance of our devices is only a few kiloohms owing to the perfect Fermi level alignment between Fe3GaTe2 and InSe, making them highly compatible with complementary metal-oxide-semiconductor circuits. This work lays a solid foundation for future stable multi-state memory applications.

Two-dimensional tellurium (Te) has been intensely studied in recent years due to its outstanding electrical properties and excellent air stability. Simple and effective contact engineering is highly desirable to further improve its device performance. In this work, we demonstrate a simple strategy to largely improve the metal–Te contact quality by forming an ultrathin tellurium oxide layer in the contact region via O2 plasma treatment. The surface oxide doped the underlying Te layers degenerately due to charge transfer, establishing an Ohmic contact between Pd electrode and Te with negative Schottky barrier under flatband condition. This enables Te field-effect transistor to achieve outstanding electronic performance, including a record-low contact resistance of ∼0.16 kΩ·μm and a high field-effect mobility of ∼1015 cm2V−1s−1 (∼3002 cm2V−1s−1) at room temperature (low temperature). The simplicity and CMOS compatibility of O2 plasma treatment make it a promising candidate for applications in Te-based large-scale integrated circuits.

Ferromagnetic semiconductors, coupling charge transport and magnetism via electrical means, show great promise for spin-based logic devices. Despite decades of efforts to achieve such co-functionality, maintaining ferromagnetic order at room temperature remains elusive. Here, we address this long-standing challenge by implanting dilute Co atoms into few-layer black phosphorus through atomically-thin boron nitride diffusion barrier. Our Co-doped black phosphorus-based devices exhibit ferromagnetism up to room temperature while preserving its high mobility (~ 1000 cm 2 V - 1 s - 1 ) and semiconducting characteristics. By incorporating ferromagnetic Co-doped black phosphorus into magnetic tunnel junction devices, we demonstrate a large tunnelling magnetoresistance that extends up to room temperature. This study presents a new approach to engineering ferromagnetic ordering in otherwise nonmagnetic materials, thereby expanding the repertoire and applications of magnetic semiconductors envisioned thus far.

Information technology has a great demand for magnetoresistance (MR) sensors with high sensitivity and wide-temperature-range operation. It is well known that space charge inhomogeneity in graphene (Gr) leads to finite MR in its pristine form, and can be enhanced by increasing the degree of spatial disorder. However, the enhanced MR usually diminishes drastically as the temperature decreases. Here, by stacking a van der Waals ferromagnet Fe3GeTe2 (FGT) on top of graphene to form an FGT/Gr heterostructure, we demonstrate a positive MR of up to ~9400% under a magnetic field of 9 T at room temperature (RT), an order of magnitude larger MR compared to pure graphene. More strikingly, the giant MR of the FGT/Gr heterostructure sustains over a wide temperature range from RT down to 4 K. Both control experiments and DFT calculations show that the enhanced MR originates from spin-dependent orbital coupling between FGT and graphene, which is temperature insensitive. Our results open a new route for realizing high-sensitivity and wide-temperature-range MR sensors. Graphene is known to exhibit a magnetoresistance, however, in pristine graphene, the magnetoresistance is highly temperature sensitive. Here, by combining graphene with Fe3GeTe2, Huang et al find a strongly enhanced magnetoresistance that is temperature insensitive.

The growth process of SiC epitaxial graphene at low pressure has been investigated systematically. Transition from buffer layer to full monolayer graphene undergoes several stages including graphene nanoribbon nucleation, directional growth and full merging. The morphologies and structures of the graphene at different stages are characterized by scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The anisotropic growth mechanism of epitaxial graphene has been revealed by statistical analysis of the shapes and sizes of graphene nanoribbons (width ranges from 40 to 300 nm with a maximum length L-perpendicular to of similar to 1.08 mu m). It is found that silicon sublimation rate plays a critical role in determining the anisotropic growth of nanoribbons, which is further confirmed by the evolution of the characterized sizes of nanoribbons at different growth stages.

The development of energy-efficient spin-based hybrid devices that can perform functions such as logic, communication, and storage requires the ability to control and transport highly polarized spin currents over long distances in semiconductors. While traditional semiconductors such as silicon support spin transport, the effects of carrier type and concentration on important spin parameters are not well understood due to the need for extrinsic doping, which can cause additional momentum and hence spin scattering. Two-dimensional semiconductors, on the other hand, offer the ability to tune carrier type and concentration through field effect gating and inherently have long intrinsic spin lifetimes, making them a desirable platform for spin transport. Here, we study gate-tunable spin transport across narrow band-gap black phosphorus-based spin valves which enable us to systematically investigate spin transport with varying hole and electron concentrations under non-local geometry. Our findings demonstrate exceptional pure spin transport that approaches intrinsic limit, particularly in the low hole doping range. We achieved record non-local signals reaching 350 Ω and spin lifetimes exceeding 16 ns. Contrary to the behaviour seen in typical semiconductors, we find that the spin transport performance of holes in black phosphorus is significantly better than that of electrons, with the Elliott-Yafet process being the primary spin scattering mechanism. The observation of gate-tunable nanosecond spin lifetimes and colossal pure spin signals in both p- and n-type black phosphorus offers promising prospects for the development of novel semiconducting spintronics devices requiring sharp p-n interfaces.

To address the challenge of low external quantum efficiency (EQE) in green micro-light-emitting diodes (micro-LEDs), we systematically investigated the effects of circular, square, and hexagonal mesa geometries. Through comprehensive fabrication and characterization, we demonstrate that the hexagonal mesa geometry significantly enhances device performance, achieving an optical output power density of 4.94 W/cm2 at 200 A/cm2, representing 1.57-fold and 1.28-fold enhancements compared to the square and circular configurations, respectively. Furthermore, it exhibits the lowest efficiency droop ratio among the geometries, and its peak EQE represents 1.18-fold and 1.13-fold enhancements compared to the circular and square configurations. These improvements are attributable to a minimized perimeter-to-emission area ratio that effectively suppresses Shockley-Read-Hall non-radiative recombination, and improved current spreading resulting from the reduced distance from the electrode edge to the mesa edge. These findings underscore the effectiveness of geometric optimization in significantly enhancing the optoelectronic performance of InGaN-based green micro-LEDs, providing a feasible strategy to achieve uniform current spreading and high quantum efficiency in micro-LEDs for integrated pixel architectures.

Sensitive avalanche photodetectors (APDs) that operate within the ultraviolet spectrum are critically required for applications in detecting fire and deep-space exploration. However, the development of such devices faces significant challenges, including high avalanche breakdown voltage, the necessity for complex quenching circuits, and thermal runaway associated with Geiger-mode avalanche operation. To mitigate these issues, we report on a 4H-SiC APD design utilizing micro-holes (MHs) structures and Al nano-triangles (NTs) to enhance surface electric field driven by strong localized surface plasmon excitations and lightning-rod effect. The device demonstrates a low avalanche breakdown voltage of approximately 14.5 V, a high detectivity of 2 × 10 13 Jones, a nanosecond-level response time, and repeated stable detections without the requirement of a quenching circuit. Collectively, when compared with the conventional wide-bandgap-based APDs, this device achieves a reduction in avalanche breakdown voltage by an order of magnitude. Consequently, the proposed APD configuration presents a promising candidate for ultraviolet detection and integrated optoelectronic circuits.

In this Letter, a GaN-based vertical Hall device is designed and experimentally fabricated, offering an effective solution for in-plane magnetic field detection. By introducing a shallow trench structure between the excitation and sensing electrodes, the short-circuit current flowing into sensing contacts in GaN-based vertical Hall devices was strongly suppressed. Through TCAD simulation analysis, the optimal range of the shallow trench depth was determined, which was then confirmed by the experimental data. From the experimental results, the sensitivity was found to be improved by 4674.7%, from 3.8 to 177.6 mV/AT, while nonlinearity was reduced by 95.5%, from 19.17% to 0.87%. The effects of device width and sensing electrode length on the device performance were also investigated in detail. Finally, this work experimentally validated the device's angle detection capability, indicating that the GaN-based vertical Hall sensor could be combined with the currently well-established horizontal Hall sensors to create high-performance monolithic integrated three-dimensional Hall sensors.

4H-SiC-based ultraviolet (UV) photodetectors (PDs) are urgently required for applications in flame detection and secure communication. However, these devices are hindered by their low quantum efficiency properties and sluggish response speed. Here, a substantial enhancement in UV detection is implemented by integrating periodic triangular Al/Al2O3 Core-Shell Nanoparticles (NPs) Arrays into 4H-SiC metal-semiconductor-metal (MSM) PDs. The detector exhibits an extremely low dark current (5.0 × 10-14 A) and a peak responsivity of 2.14 A W-1, corresponding to an external quantum efficiency of 984%. A high detectivity of 1.22 × 1014 Jones is achieved under illumination of 270 nm wavelength light at 30 V, while an ultra-high response speed is obtained with a rise time of 0.74 ns and a fall time of 1.47 ns. The improvement is attributed to the coupling between the lightning rod effect at the tips of the triangular NPs within the electrostatic field and localized surface plasmon resonance (LSPR), as well as the LSPR coupling effect between NPs, which enhances the electric field of the devices and triggers a localized avalanche effect. These results highlight the wide application and potential of NPs-enhanced 4H-SiC-based UV PDs in high-speed and high-precision detection.

High-quality epitaxial graphene is prepared on semi-insulated 4H-SiC (0001) by ultra-high vacuum thermal decomposition method and used in graphene/SiC/graphene ultraviolet-visible dual-band photodetectors. The dual-band detector exhibits an extremely low dark current (5.2 x 10-14 A) and a peak responsivity of 1.17 A W-1 corresponding to an external quantum efficiency of 518%. A high detectivity of 3.14 x 1014 Jones is achieved under 280 nm light illumination at 30 V, while a high response speed is obtained with a rise time of 25.17 ns and a decay time of 540.10 ns. The detector shows a responsivity of 1.4 x 10-5 A W-1 and a detectivity of 6.5 x 109 Jones under 430 nm light illumination. The dual-band detector equipped with SiC grating and asymmetrical graphene electrodes is demonstrated for high-performance optoelectronic logic "AND" gate with high detectivity at 280 and 430 nm. A UV-visible dual-band photodetector with grating structure and asymmetrical graphene electrodes is introduced. Light absorption is improved by grating structure. More importantly, the electric field distribution of the device is optimized by asymmetrical electrodes, leading to a complete depletion region and the local avalanche effect. The device exhibits high optoelectronic performance and can be used as optoelectronic logic gate. image

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage (V fb) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NO x ) y compounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NO x ) y . These findings provide valuable insights for SiC power devices in space applications.

Semiconductor spintronics has brought about revolutionary application prospects in future electronic devices. The tunnel junction plays a key role in achieving efficient spin injection in semiconductors. This work employed the GaN semiconductor as a room-temperature spin injection system, taking advantage of its weak spin–orbit coupling and spin scattering. By introducing a lattice-matched AlN barrier layer to improve the tunneling interface, advanced spin injection and transport were realized compared with traditional oxide barriers. The spin polarization was further improved by modulating the applied bias, and a bias-controlled tunneling enhancement mechanism was revealed. Consequently, we demonstrated a high record of spin polarization of 20.5%. This work paves a feasible route for achieving efficient spin injection and transport in GaN, which will further promote the development of room-temperature and high-performance spintronic devices.

Thermal oxidation and hydrogen annealing were applied on a 100 μm thick Al-doped p-type 4H-SiC epitaxial wafer to modulate the minority carrier lifetime, which was investigated by microwave photoconductive decay (μ-PCD). The minority carrier lifetime decreased after each thermal oxidation. On the contrary, with the hydrogen annealing time increasing to 3 hours, the minority carrier lifetime increased from 1.1 μs (as-grown) to 3.14 μs and then saturated after the annealing time reached 4 hours. The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes. Moreover, the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed. The average minority carrier lifetime was up to 1.94 μs and non-uniformity of carrier lifetime reached 38% after 4-hour hydrogen annealing. The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms.

In this brief, high-performance $8\times8$ arrays of 4H-SiC p-i-n ultraviolet (UV) photodiodes (PDs) with micro-hole structure are demonstrated. In order to improve the performance of the device, a periodic micro-hole structure (diameter = $4~\mu \text{m}$ ) was etched from the cap layer (p + layer) to the i layer, which will elevate the effective absorption of UV light. The pixels in 4H-SiC p-i-n array show a low dark current of less than $2\times 10^{-{14}}$ A and a high yield of 98.4%. Devices with 4- $\mu \text{m}$ micro-hole reach a peak spectral responsivity of 0.159 A/W at 280 nm, which is 23.3% higher than that of the device without micro-hole. Moreover, the device has a faster response time of 2.2 ns and a high UV/visible rejection ratio of more than $10^{{4}}$ . The progress on the response performance is significant to the development of UV detection imaging.

The co-existence of ferromagnetism and superconductivity becomes possible through unconventional pairing in the superconducting state. Such materials are exceedingly rare in solid-state systems but are promising platforms to explore topological phases, such as Majorana bound states. Theoretical investigations date back to the late 1950s, but only a few systems have so far been experimentally identified as potential hosts. Here, we show that atomically-thin niobium diselenide (NbSe$_2$) intercalated with dilute cobalt atoms spontaneously displays ferromagnetism below the superconducting transition temperature ($T_c$). We elucidate the origin of this phase by constructing a magnetic tunnel junction that consists of cobalt and cobalt-doped niobium diselenide (Co-NbSe$_2$) as the two ferromagnetic electrodes, with an ultra-thin boron nitride as the tunnelling barrier. At a temperature well below $T_c$, the tunnelling magnetoresistance shows a bistable state, suggesting a ferromagnetic order in Co-NbSe$_2$. We propose a RKKY exchange coupling mechanism based on the spin-triplet superconducting order parameter to mediate such ferromagnetism. We further perform non-local lateral spin valve measurements to confirm the origin of the ferromagnetism. The observation of Hanle precession signals show spin diffusion length up to micrometres below Tc, demonstrating an intrinsic spin-triplet nature in superconducting NbSe$_2$. Our discovery of superconductivity-mediated ferromagnetism opens the door to an alternative design of ferromagnetic superconductors