Dual-bath electrodeposition of n-type Bi–Te/Bi–Se multilayer thin films

• N-type Bi–Te/Bi–Se multilayer thin films were deposited by electrodeposition.
• We employed a dual-bath electrodeposition process for preparing the multilayers.
• The Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains.
• The electrical conductivity increased as the number of layers was increased.
• The power factor improved by 3 times as the number of layers was increased.

N-type Bi–Te/Bi–Se multilayer thin films were prepared by dual-bath electrodeposition. We varied the number of layers from 2 to 10 while the total film thickness was maintained at approximately 1 μm. All the multilayer films displayed the X-ray diffraction peaks normally observed from individual Bi2Te3 and Bi2Se3 crystal structures, indicating that both phases coexist in the multilayer. The cross-section of the 10-layer Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains but the boundaries between the layers were not planar. The Seebeck coefficient was almost constant throughout the entire range of our experiment, but the electrical conductivity of the multilayer thin films increased significantly as the number of layers was increased. This may be because the electron mobility increases as the thickness of each layer is decreased. As a result of the increased electrical conductivity, the power factor also increased with the number of layers. The maximum power factor was 1.44 μW/(cm K2) for the 10-layer Bi–Te/Bi–Se film, this was approximately 3 times higher than that of the 2-layer sample.