  Spin-polarized light-emitting diodes (spin-LEDs) convert the electronic spin
information to photon circular polarization, offering potential applications
including spin amplification, optical communications, and advanced imaging. The
conventional control of the emitted light's circular polarization requires a
change in the external magnetic field, limiting the operation conditions of
spin-LEDs. Here, we demonstrate an atomically thin spin-LED device based on a
heterostructure of a monolayer WSe2 and a few-layer antiferromagnetic CrI3,
separated by a thin hBN tunneling barrier. The CrI3 and hBN layers polarize the
spin of the injected carriers into the WSe2. With the valley optical selection
rule in the monolayer WSe2, the electroluminescence exhibits a high degree of
circular polarization that follows the CrI3 magnetic states. Importantly, we
show an efficient electrical tuning, including a sign reversal, of the
electroluminescent circular polarization by applying an electrostatic field due
to the electrical tunability of the few-layer CrI3 magnetization. Our results
establish a new platform to achieve on-demand operation of nanoscale spin-LED
and electrical control of helicity for device applications.
