Strain-induced circular photogalvanic current in Dirac semimetal Cd ₃ As ₂ films epitaxied on a GaAs(111)B substrate

Dirac semimetal (DSM) Cd₃As₂ has drawn great attention for exploring the novel quantum phenomena and high-speed optoelectronic applications. The circular photogalvanic effect (CPGE) current, resulting from the optically-excited spin orientation transport, was theoretically predicted to vanish in an ideal Dirac system due to the symmetric photoexcitation about the Dirac point. Here, we reported the observation of the CPGE photocurrent in epitaxial Cd₃As₂ thin films grown on a GaAs(111)B substrate. The signature of the CPGE is confirmed by its sign reversal upon switching the helicity of optical radiation, as well as its dependence on the excitation incident angle and power. By comparison of the CPGE response between the films with different thicknesses, it is suggested that the observed CPGE results from the reduced structure symmetry and substantially modified electronic band structure of the Cd₃As₂ thin film that undergoes large epitaxial strain. Our experimental findings provide a valuable reference for the band engineering and exotic helicity-dependent photocurrent phenomena in DSMs towards their potential opto-spintronic device applications.