For an arsenic donor atom in a doped silicon semiconductor, assume that the “extra” electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account the dielectric constant K = 12 of the Si lattice (which represents the weakening of the Coulomb force due to all the other atoms or ions in the lattice), and estimate
(a) The binding energy, and
(b) The orbit radius for this extra electron.