Spin-polarized light-emitting diodes based on CrI₃ operating without external spin injection

Spin-polarized light-emitting diodes convert electron spin into circularly polarized light, enabling direct optical readout of spin information and applications in on-chip information processing. Previous demonstrations have largely relied on GaAs-based emitters integrated with spin injectors. These devices, however, require complex epitaxial growth, limiting integration, while high circular polarization remains difficult, demanding high-quality materials for efficient spin injection, coherent spin transport, and spin-conserving radiative recombination. Here, we report an alternative approach for spin-polarized light-emitting diodes by employing monolayer CrI₃ as the emitter, sandwiched between two graphene/hexagonal boron nitride tunneling contacts. Although these contacts inject unpolarized carriers into CrI₃, the resulting electroluminescence exhibits circular polarization, with helicity governed by the magnetic order of CrI₃. Notably, the electroluminescence degree of polarization reaches 20% and its helicity can be reversed with a low magnetic field (~0.17 T). Combined with the inherent integrability of heterostructures, this approach provides a promising platform for future on-chip spin-optoelectronics.