Mixed‐Dimensional GaN/AlN Microwires/Graphene/u‐GaN Van der Waals Heterojunctions for High‐Performance Hot‐Electron Transistors and Ultraviolet Photodetectors

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.