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Structural defects and electronic phase diagram of topological insulator bismuth telluride epitaxial films

In this work, bismuth telluride films are grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates, using stoichiometric Bi2Te3 and additional Te solid sources. The growth dynamics and structural defects are investigated in detail as function of substrate temperature, Bi2Te3 flux and extra Te supply, by means of atomic force microscopy, Raman spectroscopy and reciprocal space mapping. The growth rate increases linearly with the Bi2Te3 flux and the most appropriate conditions to grow high-quality Bi2Te3 single layers is found to be in a narrow window of MBE parameters. At low growth temperatures Te clusters are formed, while the Te deficit increases with raising substrate temperature and decreasing deposition rate. It results in films with Bi-richer phases due to the formation of Bi double layers in between Bi2Te3 quintuple layers. The electronic transport properties are also studied by temperature dependent resistivity and Hall measurements. By properly changing the substrate temperature and/or the extra Te supply, the behavior of the films can vary from insulating to metallic as well as the major carriers from p- to n-type. The electronic phase diagram presented here provides a fast route to control the bulk conductance properties of bismuth telluride, which enables the production of intrinsic bulk insulating films. In addition, the results suggest the possibility of growing intrinsic sharp p-n junctions of Bi2Te3 by properly monitoring the occurrence of structural defects, which is the first step for practical applications of this topological insulator material.