The Construction and Mechanism Study of High‐Speed Carrier Transport Channel in Gallium Arsenide Homojunction Toward High‐Performance Photoelectrochemical Photodetector

Abstract The energy band structure and surface/interface properties are prerequisite for not only preserving the intrinsic material quality but also manipulating carrier transport behavior for photoelectrochemical (PEC) photodetection. How to precisely design/regulate the band structure and surface/interface properties of semiconductor materials is the key to improving the performance of PEC photodetection. Herein, the quintuple heterotypic homojunction (QH) GaAs film is fabricated with a gradient energy band via plasma‐assisted molecular beam epitaxy for constructing a high‐speed carrier transport channel in PEC photodetection, which can efficiently drive the separation and transport of photogenerated electron‐hole pairs. The designed QH‐GaAs‐based PEC photodetector exhibits excellent performances, compared with bare i‐GaAs, delivering an ultrashort rise/decay times of only 1.1/1.1 ms and a high responsivity of 20.4 mA W⁻¹ at 0 V under 850 nm illumination. Strikingly, an ultrahigh detectivity with 1.46 × 10¹² Jones is achieved. More importantly, the QH‐GaAs device can stably operate underwater seawater environment. This study provides a novel strategy for designing and fabricating multiple heterotypic homojunction with gradient energy band to boost charge transport dynamics for PEC fields.