The electric properties of a single crystal bismuth telluride doped with a small concentration of Erbium, Bi_2-xEr_xTe₃ with x = 0.002, are investigated as a function of temperature. The resistivity was obtained by using the van der Pauw method. The measured electrical resistivity is 78µΩcm at 4.2 K. The charge density of Bi_2-xEr_xTe₃ is found to be at 4.2 K. It turns out that Bi_2-xEr_xTe₃ is a p-type semiconductor. It is discussed that the high mobility and less density support that Bi_2-xEr_xTe₃ is a potential sensor with high energy resolution. Comparison with an established material (i.e. Au:Er alloy) is also discussed.