(a)For Ge:
N_A = 1.74e+015 /cm^3
N_D = 1.64e+015 /cm^3
Therefore barrier potential energy for Ge = 0.22 eV

(b)For Si:
N_A = 6.25e+015 /cm^3
N_D = 4.81e+015 /cm^3
Therefore barrier potential energy for Si = 0.666 eV