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

Spin-polarized light-emitting diodes (spin-LEDs) convert electron spin into circularly polarized light, enabling direct optical readout of spin information and opening new avenues for solid-state, on-chip information processing and cryptography. To achieve such applications, considerable research has been devoted to GaAs-based emitters integrated with spin injectors including ferromagnetic metals, dilute magnetic semiconductors, and spin-filter tunnel barriers. These conventional spin-LEDs, however, require complex epitaxial growth and their limited integrability remains a critical challenge. Additionally, achieving high circular polarization is inherently difficult, as it requires high-quality materials and interfaces to ensure efficient spin injection, coherent spin transport, and spin-conserving radiative recombination. Here, we report an alternative approach to realize spin-LEDs by employing the monolayer CrI₃ as the light-emitting layer, sandwiched between two graphene/ hexagonal boron nitride tunneling contacts. Although the exploited contacts inject unpolarized carriers into CrI₃, we show that the resulting electroluminescence could be circularly polarized, with its helicity governed by the magnetic order of CrI₃, as confirmed by helicity-resolved EL measurements and magneto-optical analysis. Notably, the EL degree of polarization reaches 20%, outperforming most conventional spin-LEDs, and its helicity can be readily reversed with a low magnetic field (~ 0.17 T). Combined with the inherent integrability of our proposed heterostructures, this approach provides a promising platform for future on-chip spin-optoelectronic devices.