Impurity orbits indium antimonidc has Eg = 0.23eV; dielectric constant = 18; electron effective mass me = 0.015m. Calculate (a) The donor ionization energy;

Impurity orbits indium antimonidc has Eg = 0.23eV; dielectric constant ε = 18; electron effective mass me = 0.015m. Calculate 

(a) The donor ionization energy; 

(b) The radius of the ground state orbit.

(c) At what minimum donor concentration will appreciable overlap effects between the orbits of adjacent impurity atoms occur? This overlap tends to produce an impurity band–a band of energy levels which permit conductivity presumably by a hopping mechanism in which electrons move from one impurity site to a neighboring ionized impurity site.