Demonstration of large field effect in topological insulator films via a high-$\kappa $ back gate

In topological insulators (TI) the spins are locked to opposite momentum direction when the Fermi level passes through Dirac point of its helical surface states, and the electrical field effect is a very promising way to modulate TI spins for spintronic devices. We have fabricated the back gate structure by growing TI films on high-$\kappa $ oxide layers including amorphous oxides of Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ deposited on conducting substrates for applying the field effect with smaller operating voltage compared to SiO$_{\mathrm{2}}$, and keeping the top surface entirely open for subsequent fabrications of FM/TI, SC/TI structures intended for various studies. For Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ grown on these amorphous oxide thin films, streaky RHEED patterns indicated the film is highly crystalline. Weak antilocalization effect was observed to verify the time-reversal symmetry protected transport property. Very large field effect was demonstrated; for example, in the 6QL samples we are able to modulate as much as 2E13 cm$^{\mathrm{-2\thinspace }}$holes in applying negative gate bias. Field effect of Sb doped Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ to realize sign reversal of carrier concentration will also be presented.