Circular Photogalvanic Current in Ni-Doped Cd3As2 Films Epitaxied on GaAs(111)B Substrate.

Magnetic element doped Cd3As2 Dirac semimetal has attracted great attention for revealing the novel quantum phenomena and infrared opto-electronic applications. In this work, the circular photogalvanic effect (CPGE) was investigated at various temperatures for the Ni-doped Cd3As2 films which were grown on GaAs(111)B substrate by molecular beam epitaxy. The CPGE current generation was found to originate from the structural symmetry breaking induced by the lattice strain and magnetic doping in the Ni-doped Cd3As2 films, similar to that in the undoped ones. However, the CPGE current generated in the Ni-doped Cd3As2 films was approximately two orders of magnitude smaller than that in the undoped one under the same experimental conditions and exhibited a complex temperature variation. While the CPGE current in the undoped film showed a general increase with rising temperature. The greatly reduced CPGE current generation efficiency and its complex variation with temperature in the Ni-doped Cd3As2 films was discussed to result from the efficient capture of photo-generated carriers by the deep-level magnetic impurity bands and enhanced momentum relaxation caused by additional strong impurity scattering when magnetic dopants were introduced.

Ultrafast Optical Probe of Coherent Acoustic Phonons in Dirac Semimetal Cd3As2 Film Epitaxied on GaAs(111)B Substrate.

Coherent longitudinal acoustic phonon (CAP) generation in epitaxial Dirac semimetal Cd3As2 films with different thicknesses was investigated by a time-resolved reflectance technique. The short-lived weak CAP oscillations can be observed only in the thicker Cd3As2 films, and their central frequency of 0.039 THz has no dependence on sample thickness, but is nearly inversely proportional to the probe wavelength. For the 20 nm thin film, the observed long-lived CAP with a central frequency of 0.049 THz is generated in the GaAs(111)B substrate underneath. A sound velocity of 3800 m/s for the Cd3As2 film and 5360 m/s for the GaAs(111)B substrate is thus deduced. In addition, the opposite CAP amplitude and lifetime dependence on temperature further confirms the electronic and thermal stress origination of CAP generated in GaAs(111)B and Cd3As2 film, respectively, based on the propagating strain pulse model. The central frequency of CAP is found to be stable with increasing pumping fluence and temperature, which makes Cd3As2 a potential material for thermoelectric device applications.

Strain-induced circular photogalvanic current in Dirac semimetal Cd3As2 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.