Q$2(5$ points$)$:

$($a$)$ A semiconductor has equal electron and hole concentration of $4\mathrm{.}2{10}^8{m}^{-3}.$ On

doping with an impurity, electron concentration increases to $6{10}^{12}{m}^{-3}*[2$ points$]$

$($i$)$Identify the new semiconductor obtained after doping $.$

$($ii$)$ Calculate the new hole concentration.

$($b$)$ On the basis of energy band diagrams, distinguish between metals, insulators and

semiconductors giving numbers for the band gap in each case. $[3$ points$]$