  Topological insulators possess a non-conductive bulk and present surface
states, henceforth, they are electrically conductive along their boundaries.
Bismuth selenide ($Bi_2Se_3$) is one of the most promising topological
insulators. However, a major drawback is its n-type nature arising from its
natural doping, which makes the transport in the bulk dominant. This effect can
be overcome by shifting the chemical potential into the bandgap, turning the
transport of the surface states to be more pronounced than the bulk
counterpart. In this work, $Bi_2Se_3$ was grown by molecular beam epitaxy and
doped with 0.8, 2, 7, and 14 at. % of Ga, with the aim of shifting the chemical
potential into the bandgap. The structural, morphological, and electronic
properties of the Ga doped $Bi_2Se_3$ are studied. Raman and X-ray diffraction
measurements confirmed the incorporation of the dopants into the crystal
structure. Transport and magnetoresistance measurements in the temperature
range of 1.5 to 300 K show that Ga-doped $Bi_2Se_3$ is n-type with a bulk
charge carrier concentration of $10^{19} cm^{-3}$. Remarkably, magnetotransport
of the weak antilocalization effect (WAL) measurements confirm the existence of
surface states up to a doping percentage of 2 at. % of Ga and coherence length
values between 50-800 nm, which envisages the possibility of topological
superconductivity in this material.
