| Summary: | Cd _3 As _2 is a new kind of three-dimensional (3D) Dirac semimetal with extraordinary carrier mobility, which can be viewed as ‘3D graphene’. Theory predicts that Cd _3 As _2 can be driven into a quantum spin Hall insulator with a sizeable band gap by reducing dimensionality. In this letter, we report the systematic growth of undoped Cd _3 As _2 thin films with the thickness of 50 ∼ 900 nm by molecular beam epitaxy. The magneto-transport study on these single-crystalline films shows a high mobility in the range of 3.8 ∼ 9.1 × 10 ^3 cm ^2 · V ^−1 · s ^−1 and a relative low electron concentration of 1 ∼ 8 × 10 ^17 cm ^−3 . Significantly, a thickness-induced semimetal-to-semiconductor transition was observed. In contrast with what is expected in the bulk counterpart, the 50 nm-thick Cd _3 As _2 film exhibits semiconducting characteristics, witnessing an emerged bandgap opening when the dimensionality is reduced. Finally, the analyses on the temperature- and angular-dependence of magneto-resistance and Shubnikov-de Hass oscillations reveal a non-trivial to trivial Berry’s phase transition that is in connection with the reduced dimensionality. Our results demonstrate that the Cd _3 As _2 thin films with unique electronic structure and high mobility hold promise for Dirac semimetal device applications.
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