Intrinsic Polarization-Induced Enhanced Ferromagnetism and Self-Doped p–n Junctions in CrBr₃/GaN van der Waals Heterostructures

Abstract

Two-dimensional (2D) ferromagnetic (FM) semiconductors with a high Curie temperature and tunable electronic properties are a long-term pursuing target for the development of high-performance spin-dependent optoelectronic devices. Herein, on the basis of density functional theory calculations, we report a new strategy to tune the Curie temperature and electronic structures of a ferromagnetic CrBr₃ monolayer through the formation of CrBr₃/GaN van der Waals heterostructures. Our calculated results demonstrate that the Curie temperature and band alignment of CrBr₃/GaN heterostructures strongly depend on the thickness and polarization direction of the GaN layer. The combination of the CrBr₃ monolayer with N-terminated GaN nanosheets leads to enhanced FM coupling via superexchange interactions between the Cr-<i>t</i>_2g and Cr-e_g orbitals, consequently resulting in a Curie temperature of CrBr₃ of up to 67 K. Moreover, self-doped p-n junctions can be naturally formed in the heterostructures without additional modulation of external fields. The enhanced FM coupling and self-doping effect in the heterostructures are associated with the intrinsic polarization of the GaN layer that drives interfacial electron transfers from GaN to CrBr₃. Therefore, this work not only offers an efficient scheme to boost the Curie temperature of the CrBr₃ monolayer but also opens up a new route to realize nonvolatile van der Waals p-n junctions.