Fangliang Gao

To address short‐channel effects and high‐power consumption arising from the miniaturization of conventional silicon‐based devices, hot‐electron transistors (HETs) have emerged as promising candidates owing to their exceptional ultrafast carrier transport capabilities. Herein, we fabricate mixed‐dimensional vertical van der Waals heterojunction HETs by integrating one‐dimensional (1D) GaN/AlN microwires, two‐dimensional (2D) monolayer graphene, and three‐dimensional (3D) undoped bulk GaN, which combines the wide‐bandgap characteristics of GaN and the superior properties of low‐dimensional materials. Via rational band engineering, the device achieves a common‐base current collection efficiency of 99.9% and a common‐emitter current gain of 11.9. Driven by the intrinsic built‐in electric field of the heterojunction, the device supports three operational modes for ultraviolet (UV) photodetection, featuring an ultralow dark current, self‐powered photoresponse, and high sensitivity. This work verifies the great potential of GaN‐based mixed‐dimensional van der Waals heterostructures for electronic amplification and UV photodetection. It also provides a viable device platform and innovative strategies for developing monolithic multifunctional optoelectronic chips toward next‐generation intelligent optoelectronic systems, including UV communication and high‐sensitivity environmental monitoring.

Spin–orbit torque (SOT) technology stands at the forefront of next‐generation non‐volatile memory and logic computing, promising superior endurance and ultrafast dynamics compared to conventional spin‐transfer torque (STT) architectures. However, the persistent requirement of an external magnetic field for deterministic switching of perpendicular magnetization severely impedes high‐density integration and commercial viability. This review systematically evaluates the evolutionary trajectory of symmetry‐breaking strategies developed to overcome this bottleneck. The analysis progresses from early macroscopic structural engineering, such as wedged geometries and lateral asymmetries, to mesoscopic built‐in effective fields driven by interfacial exchange coupling and chiral spin textures. Crucially, we identify a defining paradigm shift in the field: the transition from complex geometric modifications toward intrinsic material‐level innovations, including low‐symmetry crystals, vertical composition gradients (VCG), and synergistic dual‐torque (STT‐SOT) architectures. By resolving the trade‐offs among switching efficiency, thermal stability, and structural complexity, these intrinsic and hybrid approaches offer a practical roadmap for integrating scalable, all‐electrical SOT‐MRAM with standard CMOS back‐end‐of‐line (BEOL) processes. Finally, we establish a dual‐track strategic roadmap: while long‐term breakthroughs require parallel exploration of new exotic physics, we underscore the importance of focusing on mass production and foundry scalability at the current stage.

This review comprehensively explores the cutting-edge applications of gallium nitride (GaN) and two-dimensional transition metal dichalcogenides (TMDs) heterojunctions in next-generation high-performance devices. With a strong focus on practical implementation, we systematically analyze the pivotal roles of GaN/TMDs heterostructures across electronics, optoelectronics, sensing, and energy conversion. Key advancements in high-frequency transistors, low-power neuromorphic computing, broadband photodetectors (UV to NIR), self-powered sensors, and efficient photocatalytic systems are highlighted. The discussion extends to innovative fabrication techniques enabling large-area integration and flexible electronics. Furthermore, we showcase their application potential in strategic fields such as 5G communication, artificial intelligence, imaging systems, environmental monitoring, and clean energy technologies. By addressing critical challenges in interface engineering, material synthesis, and device integration, this review provides a valuable roadmap for developing high-performance, commercially viable semiconductor devices.

Janus monolayers with broken out-of-plane symmetry provide a natural platform for built-in polarization and internal electric fields, offering new opportunities for ultrathin spintronic device design. Here, based on spin-polarized density functional theory and the nonequilibrium Green’s function formalism (DFT‐NEGF), we investigate the intrinsic properties of the Janus 1T‐CrSBr monolayer and its spin-transport behavior in conceptual nanodevices. Both the pn-junction diode and the p-i-n junction field-effect transistor (FET) exhibit fully spin-polarized transport and pronounced rectification, whereas the n-i-n junction device shows clear negative differential resistance (NDR). These results highlight Janus 1T‐CrSBr as a multifunctional 2D spintronic material that can integrate diode, transistor, and NDR-element characteristics.

The demand for single-photon high-sensitivity ultraviolet (UV) detection is continuously increasing in cutting-edge fields such as UV astronomy, environmental monitoring, and space communications. In particular, gallium nitride (GaN) is an ideal material for UV detection due to its wide bandgap (3.4 eV), strong radiation immunity, and visible/solar-blind properties. In this respect, avalanche photodetectors (APDs) are very promising candidates for single-photon UV detection due to their high sensitivity, large gain, high detection efficiency, and room temperature operation. This review summarizes the GaN avalanche breakdown characteristics, including current surge, positive temperature coefficient of Vbr, and non-linear characterization. In addition, recent advances in various structural types of GaN APDs, such as p-i-n, separated absorption multiplication, optimized edge termination, and polarization-enhanced structures, are presented. In addition, the directions and challenges for the future development of GaN APDs are discussed. Although GaN-based APDs have significantly improved their UV single-photon detection performance through structural innovations, noise control, linearity optimization, and process simplification remain the core challenges. In the future, the integration with two-dimensional material heterojunction and new light trapping structure is expected to break through the existing bottleneck and promote its application in frontier fields such as deep space exploration and quantum communication.

This study pioneers a high-performance UV polarization-sensitive photodetector by ingeniously integrating non-centrosymmetric metal nanostructures into a graphene (Gr)/Al₂O₃/GaN heterojunction. Unlike conventional approaches constrained by graphene’s intrinsic isotropy or complex nanoscale patterning, our design introduces asymmetric metal architectures (E-/T-type) to artificially create directional anisotropy. These structures generate plasmon-enhanced localized electric fields that selectively amplify photogenerated carrier momentum under polarized UV light (325 nm), synergized with Fowler-Nordheim tunneling (FNT) across an atomically thin Al₂O₃ barrier. The result is a breakthrough in performance: a record anisotropy ratio of 115.5 (E-type, −2 V) and exceptional responsivity (97.7 A/W), surpassing existing graphene-based detectors by over an order of magnitude. Crucially, by systematically modulating metal geometry and density, we demonstrate a universal platform adaptable to diverse 2D/3D systems. This study provides a valuable reference for developing and practically applying photodetectors with higher anisotropy than ultraviolet polarization sensitivity.