In a pure silicon crystal,the electron-hole concentration is $10^{16} \ m^{-3}$ at $301 \ K$. Now,$10^{21}$ atoms of phosphorus are added per cubic metre. The new hole concentration in silicon is (in per $m^3$):

In a junction diode,the holes are due to

Through a semiconductor,an electric current is due to the drift of

Statement-$I$: By doping silicon semiconductor with pentavalent material,the electron density increases.
Statement-$II$: The $n$-type semiconductor has a net negative charge.
In the light of the above statements,choose the most appropriate answer from the options given below:

Explain the recombination coefficient of an intrinsic semiconductor and derive the relation $n_i^2 = n_e n_h$.

$A$ $Ge$ specimen is doped with $Al$. The concentration of acceptor atoms is $10^{21} \text{ atoms}/m^3$. Given that the intrinsic concentration of electron-hole pairs is $10^{19} /m^3$, the concentration of electrons in the specimen is: