Write a note on $n$-type and $p$-type semiconductors.

(N/A) $n$-type semiconductors: These are formed when group $14$ elements (like $Si$ or $Ge$) are doped with group $15$ elements (like $P$ or $As$). The dopant has $5$ valence electrons,$4$ of which form covalent bonds with the host atoms,leaving one extra electron free to conduct electricity. Since the charge carriers are electrons (negative charge),they are called $n$-type semiconductors.
$p$-type semiconductors: These are formed when group $14$ elements are doped with group $13$ elements (like $B$ or $Al$). The dopant has only $3$ valence electrons,creating an electron vacancy or 'hole' in the crystal lattice. These holes move through the crystal,allowing for electrical conductivity. Since the charge carriers are effectively positive holes,they are called $p$-type semiconductors.