Transition from n-type to p-type topological insulator thin films of Bi$_{2}$Te$_{3}$

By using angle-resolved photoemission spectroscopy, we have investigated the electronic structure of the Bi$_{2}$Te$_{3}$ films on Si(111) prepared by molecular beam epitaxy. It is found that the Bi$_{2}$Te$_{3}$ films change from n-type to p-type topological insulator when the growth mode changes layer-by-layer to step-flow, for a given beam flux ratio of Te$_{2(4)}$/Bi. In situ scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal formation of different defects, i. e., Te$_{Bi}$ and Bi$_{Te}$ antisite defects, which are responsible for the n- and p-type conductivity transition. A mechanism for the transition is proposed based on the STM experiment and first-principles calculations. The work suggests a simple way to regulating the chemical potential and Dirac fermion density on the surface of a topological insulator without external doping.