Preferential growth of Bi _2Te _3 films with a nanolayer structure: Enhancement of thermoelectric properties induced by nanocrystal boundaries

摘要

Preferential growth of different crystal planes in layered Bi _2Te _3 thin films with each layer < 40 nm has been achieved by a simple magnetron co-sputtering method. The preferential growth of (015) plane or (001) was achieved at special depositing conditions due to the more sufficient growth along the in-plane direction induced by the enhanced diffusion of atoms and lower deposition rate. The Bi _2Te _3 film with preferential growth of (001) plane possesses about two times higher electrical conductivity and Seebeck coefficient as compared to the film with preferential growth of (015) plane, due to the greatly enhanced carrier mobility. Furthermore, the thermal conductivity has been suppressed due to more phonon scattering at grain boundaries, compared with ordinary Bi _2Te _3 alloys and films.