Chalcogens are extremely promising for hyperdoping Si because of their superior electronic properties with respect to group V elements of the periodic table traditionally employed as dopants. Within the framework of plane-wave pseudopotential techniques we computed the formation energy of different types of defects formed by dopants in Se-hyperdoped Si, as a function of the dopant concentration. Moreover, we studied the possibility of tailoring the electronic properties of the system, by tuning the probability that each type of defect can form. In particular, by using supercells exceeding thousands of atoms we characterized the double impurity band (IB) structure of complex, formed by a Si vacancy surrounded by three Se, which presents a shallow metallic IB and a deep insulating IB in the Si band gap, thus allowing sub-threshold photon absorption, and suggesting that a significant improvement in the …