Three-dimension (3D) Dirac semimetals are a newly discovered class of topological materials that have attracted significant interest. Their electronic structure exhibits a linear dispersion relation around the Fermi energy, making them a three-dimensional analogue of graphene. Epitaxial heterostructures of these materials open a path for the manipulation of topological electronic states by strain engineering, electron confinement, or electrostatic gating, all of which may enable new electronic devices.

Here, we discuss the growth of epitaxial thin films of Cd₃As₂, a 3D Dirac semimetal, by molecular beam epitaxy. We report on their structure, magnetotansport properties, and field gating experiments using high-k dielectrics. The films are shown to grow in the low-temperature, vacancy ordered, tetragonal Dirac semimetal phase. Extremely high room temperature mobilities (~20,000 cm²/Vs) are achieved in epitaxial layers on III-V substrates. Unusual transport characteristics are observed, such as a negative longitudinal magnetoresistance, i.e., when the magnetic field is applied parallel to the direction of electric current. We vary the film parameters and study their influence on the magnetotransport to distinguish between ‘classical’ phenomena and effects originating from the unique electronic structure.