Influence of post-deposition annealing on the transport properties of sputtered Bi₂Se₃ thin films

In the past decade, Bi₂Se₃ has been one of the most investigated TI materials. The physical properties of Bi₂Se₃ are dictated by selenium vacancies irrespective of the growth method. Controlling the number of vacancies is a challenging problem, but it can be influenced by factors such as substrate and growth temperature. In this work, we demonstrate that post-deposition annealing temperature is also effective in controlling the carrier concentration of Bi₂Se₃ thin films. Ultra-thin Bi₂Se₃ films were fabricated on quartz substrates using magnetron sputtering at room temperature, and their resistivity, bulk carrier concentration, and bulk mobility are measured as a function of post-deposition annealing temperature under vacuum conditions ranging from 180 – 350 °C. We find that carrier concentration can vary by an order of magnitude, and we obtained values as low as ~1x10¹⁹ cm^-3 between 200-250 °C which compares very well with some of the best literature reports on films made by MBE. Overall, our work demonstrates that the transport properties of Bi₂Se₃ films are highly tunable through post-annealing temperature, which may be of interest in applied areas such as nanoelectronics and spintronics.