Number of atoms per m3 in semiconductor crystal =8×1028 atoms ∕m3 Number of doped atoms =2‌ppm=2 atoms out of 106 atoms. ∴ Number of doped atoms in 8×1028 atoms ∕m3 =2×
8×1028
1×106
=16×1022‌ atoms ‌∕m3 As, each pentavalent impurity atom produces 1-electron in conduction band, number of conduction electrons =ne=4×1022 electrons ∕m3 As ne.nn=ni2,=, we have nn=