Signature of weak-antilocalization in sputtered topological insulator Bi 2 Se 3 thin films with varying thickness.

We report a low-temperature magneto transport study of Bi 2 Se 3 thin films of different thicknesses (40, 80 and 160 nm), deposited on sapphire (0001) substrates, using radio frequency magnetron sputtering technique. The high-resolution x-ray diffraction measurements revealed the growth of rhombohedral c-axis {0003n} oriented Bi 2 Se 3 films on sapphire (0001). Vibrational modes of Bi 2 Se 3 thin films were obtained in the low wavenumber region using Raman spectroscopy. The surface roughness of sputtered Bi 2 Se 3 thin films on sapphire (0001) substrates were obtained to be ~ 2.26-6.45 nm. The chemical and electronic state of the deposited Bi 2 Se 3 was confirmed by X-ray photoelectron spectroscopy and it showed the formation of Bi 2 Se 3 compound. Resistivity versus temperature measurements show the metallic nature of Bi 2 Se 3 films and a slight up-turn transition in resistivity at lower temperatures < 25 K. The positive magneto-resistance value of Bi 2 Se 3 films measured at low temperatures (2-100 K) confirmed the gapless topological surface states in Bi 2 Se 3 thin films. The quantum correction to the magnetoconductivity of thin films in low magnetic field is done by employing Hikami-Larkin-Nagaoka theory and the calculated value of coefficient 'α' (defining number of conduction channels) was found to be 0.65, 0.83 and 1.56 for film thickness of 40, 80 and 160 nm, respectively. These observations indicate that the top and bottom surface states are coupled with the bulk states and the conduction mechanism in Bi 2 Se 3 thin films varied with the film thicknesses.