The net charge on an $N-$type semiconductor is

Pure silicon at $300 \ K$ has equal electron and hole concentration of $1.5 \times 10^{16} \ m^{-3}$. If the hole concentration increases to $3 \times 10^{22} \ m^{-3}$,then the electron concentration in the silicon is

When a small amount of impurity atoms are added to a semiconductor, then generally its resistivity:

In $N$-type semiconductors,the majority charge carriers are

In a $P$-type semiconductor,there is

Why are elemental dopants for Silicon or Germanium usually chosen from group $XIII$ or group $XV$?