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2D magnetic semiconductors exhibit great potential for next‐generation spintronics, but realizing their full capabilities has been hindered by the low Curie temperatures (Tc) below 50 K observed in current materials. Here, a new mechanism to substantially enhance the Tc of 2D semiconducting materials through incorporating both in‐plane and out‐of‐plane superexchange interactions enabled by structural design is demonstrated. Specifically, monolayer Cr2Se3 is synthesized with a five‐layer Se–Cr–Se–Cr–Se atomic structure using molecular beam epitaxy (MBE). This unique structure not only possesses optimized in‐plane superexchange interaction but also incorporates out‐of‐plane Cr–Se–Cr couplings. Scanning tunneling spectroscopy (STS) and angular‐resolved photoemission spectroscopy (ARPES) confirm its semiconducting nature. Remarkably, the ferromagnetic phase transition observed by ARPES and Magnetic Force Microscopy (MFM) indicated that its Tc is up to 230 K. This not only establishes a new record for Tc in 2D ferromagnetic semiconductor materials but also introduces a novel approach to modulating materials' properties by manipulating the vertical dimension in 2D materials. [ABSTRACT FROM AUTHOR]

Bi2O2Se has established itself as a revolutionary two-dimensional (2D) semiconductor owing to its superior electric, optoelectric and thermoelectric properties. The structural compatibility between Bi2O2Se and perovskite oxides makes the investigation of their heterointerfaces an intriguing frontier. Herein, we unveil the Bi2O2Se/SrTiO3 interfacial interaction by studying the photoresponse of the oxide heteroepitaxy. The record-broad photosensitivity (365–1850 nm) is ascribed to a complex interplay between photoconductive, photogating, pyroelectric and photo-thermoelectric (PTE) effects. The distinctive pyroelectricity, which results in a 900-fold decrease in the response time, originates from the surface polarization and relaxation at the Bi2O2Se/SrTiO3 interface. Self-powered behavior is reported for the first time in Bi2O2Se-based photodetectors. Under zero bias, the PTE-dominated photoresponse gives rise to a tunable polarity and magnitude of the photocurrent, and an estimated Seebeck coefficient of −127.8 μV K−1. The optimal photoresponsivity of 12.62 A W−1, external quantum efficiency of 1424.08% and detectivity of 1.51 × 109 Jones indicate the performance advancement of the photodiodes based on as-grown Bi2O2Se. Our study sheds light on the exploitation of exotic physical phenomena at the heterointerfaces between Bi2O2Se and perovskite oxides, and also indicates that 2D Bi2O2Se has a wide range of applications in piezoelectrics, ferroelectrics, self-powered nanogenerators and optical communications. [ABSTRACT FROM AUTHOR]