Investigation of the transport properties of Bi2Se3 films grown on various substrates

Topological insulators, a new state of quantum matter, displayed a variety of physical phenomena. We have obtained high quality TI films of Bi$_{2}$Se$_{3}$, Bi$_{2}$Te$_{3}$, and Sb$_{2}$Te$_{3}$ grown on various substrates with streaky RHEED patterns and large domains 1-2um in size. However, the Fermi level of Bi$_{2}$Se$_{3}$ tends to locate in the bulk conduction band due to the high density of intrinsic defects in TIs. To fine tune the Fermi level to be within the band gap, Bi$_{2}$Se$_{3}$ films were grown on amorphous oxide layers such as SiO$_{2}$, Y$_{2}$O$_{3}$, and Al$_{2}$O$_{3}$ $\sim$20 nm thick deposited on GaAs and Si substrates in a back gate structure for the electrical field effect. Compare to Bi$_{2}$Se$_{3}$ thin films on crystalline substrates such as sapphire, samples grown on amorphous oxides such as Al$_{2}$O$_{3}$ showed lower carrier concentration for the film thickness less than 10 QL, and the resistivity showed an insulating behavior at T below 50K. Other transport properties such as mobility, WAL effects are underway.