Thickness-independent transport channels in topological insulator Bi ₂Se ₃ thin films

With high quality topological insulator Bi ₂Se ₃ thin films, we report thickness-independent transport properties over wide thickness ranges. Conductance remained nominally constant as the sample thickness changed from 256 to ∼8QL (where QL refers to quintuple layer, 1QL1nm). Two surface channels of very different behaviors were identified. The sheet carrier density of one channel remained constant at ∼3.0×1013cm ^-2 down to 2 QL, while the other, which exhibited quantum oscillations, remained constant at ∼8×1012cm ^-2 only down to ∼8QL. The weak antilocalization parameters also exhibited similar thickness independence. These two channels are most consistent with the topological surface states and the surface accumulation layers, respectively.