Fig. 1.

High-crystallinity and high-mobility Cd₃As₂ thin films. a Experimental trend of electron mobility versus sheet carrier density. Among our films (filled circle) prepared with pulsed laser deposition (PLD), high-quality ones obtained by high-temperature annealing are highlighted with bigger symbols. The mobility reaches a maximum of μ = 3 × 10⁴ cm²/Vs even at a thickness of t = 30 nm, rivaling mobility values for bulk thinned plates (diamond²²) and nanostructures (triangle²³ and  inverted triangle²⁴), while it intrinsically decreases with reducing to two dimensions. Other films (circle) grown by molecular beam epitaxy (MBE)^18,19, thermal evaporation (TE)¹⁵, or pulsed laser evaporation (PLE)¹⁶ techniques are also plotted for comparison. Inset shows the primary cubic structure of Cd₃As₂. b–d Schematic illustration of the electronic structure evolution from the 3D DSM state. With decreasing the film thickness, subbands are formed due to the quantum confinement, giving rise to two-dimensional topological insulating (2D TI) and trivial insulating (2D I) states depending on the number of inverted subbands⁶. e Cross-sectional image of a 14 nm Cd₃As₂ film sandwiched between Si₃N₄/TiO₂ cap and SrTiO₃ substrate. The length of the scale bar is 10 nm. f Atomically resolved element map of the boxed region in e, shown with the cross-sectional view of the crystal structure. g In the x-ray diffraction θ–2θ scan, Bragg peaks of the (112)-oriented Cd₃As₂ film are observed with clear Laue oscillations. The SrTiO₃ substrate peaks are marked with an asterisk