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

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-t(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.