Role of bulk and surface current carriers in resistivity of thin films of the topological insulator Bi$_2$Se$_3$

The temperature dependences of the electrical resistivity of topological insulator Bi$_2$Se$_3$ thin films with thicknesses of 20 and 40 nm were measured in the temperature range from 4.2 to 80 K. Their resistivity was shown to depend on thickness. A method was proposed for “separation” of the bulk and surface resistivity of films, with the help of which corresponding estimates were made. It was demonstrated that the surface resistivity is more than two orders of magnitude less than the bulk resistivity at $T$ = 4.2 K.