Investigation of Interface-Induced Helicity-Dependent Photocurrent and High-T_C Ferromagnetism in Wafer-Scale 2D Ferromagnetic Fe₄GeTe₂/Bi₂Te₃ Heterostructures

The helicity-dependent photocurrent (HDPC) of Fe 4 GeTe 2 (3, 5, 8, 10 nm)/Bi 2 Te 3 (8 nm) heterostructures grown on sapphire substrates was systematically investigated. It is revealed that the HDPC is induced by the interface coupling between the Fe 4 GeTe 2 and Bi 2 Te 3 films, and it is dominated by the circular photogalvanic effect (CPGE) rather than by the circular photodrag effect (circular photon drag effect). As the tensile strain increases, the CPGE current decreases, which can be attributed to the decrease of the interface-induced spin–orbit coupling with increasing tensile strain. In addition, it is demonstrated that by applying appropriate tensile strain, the 5 nm Fe 4 GeTe 2 /Bi 2 Te 3 sample can be used to detect the circular polarization state of a light. Finally, Fe 4 GeTe 2 (5, 8, and 10 nm)/Bi 2 Te 3 (8 nm) heterostructures show a T C larger than 390 K. The dependence of the CPGE on the film thickness of Fe 4 GeTe 2 is different from that of Curie temperature, indicating that the enhanced exchange interaction induced by the interface coupling may be the dominant mechanism for the high- T C ferromagnetism. The large interface-induced CPGE in the Fe 4 GeTe 2 /Bi 2 Te 3 suggests that Fe 4 GeTe 2 /Bi 2 Te 3 heterostructures may provide a good platform for designing novel opto-spintronic devices.