Explain electron-rich impurities and electron-deficient impurities in semiconductors.

(N/A) $1$. Electron-rich impurities: These are formed when group-$15$ elements (like $P$ or $As$) are doped into group-$14$ elements (like $Si$ or $Ge$). Since group-$15$ elements have $5$ valence electrons,$4$ electrons are used for covalent bonding with $Si/Ge$ atoms,and the $5$th electron remains free,creating an $n$-type semiconductor.
$2$. Electron-deficient impurities: These are formed when group-$13$ elements (like $B$ or $Al$) are doped into group-$14$ elements. Since group-$13$ elements have only $3$ valence electrons,they create an electron hole (vacancy) in the lattice,which acts as a positive charge carrier,creating a $p$-type semiconductor.