3D Dirac semimetals are an unusual class of quantum materials with unique electronic states. Topological transitions have been predicted as a result of confinement, symmetry breaking, and by the application of external electric fields. Here, we present transport studies of Cd₃As₂ films under external electric and magnetic fields.
To fabricate devices for electrostatic gating, 20 nm Al₂O₃ gate dielectrics were deposited on epitaxial Cd₃As₂ films using atomic layer deposition (ALD). An increase in sheet carrier density and decrease in mobility were observed after ALD. Capacitance-voltage characteristics show a small change in capacitance with gate bias, suggesting that the carrier modulation is occurring only at the Cd₃As₂/Al₂O₃ interface. The modulated carrier density is ~3x10¹³ cm^-2. Field effect devices show a 12% modulation in drain current.
Hall measurements show a decrease in sheet carrier density with negative gate bias. At large negative gate bias, the Hall resistance suggests a two-carrier transport, as expected if the Fermi level is near the Dirac node. Moreover, a negative to positive magnetoresistance transition is observed when gate voltage is changed from positive to negative voltage. We discuss the results in terms of the nature of the electronic states in this system.