AP EAPCET 07-Jul-2022 Shift 2 Paper

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=

ni2

ne

=

(1×1016)2

16×1022

=6.25×108‌ holes ‌∕m3