If a small amount of aluminium is added to the silicon crystal:

Which of the following is correct for \(\mathrm{n}\)-type semiconductors?

The conductivity of an n-type semiconductor whose density of conduction electrons is ${\mathrm{n}}_{\mathrm{e}}$, Density of holes is ${\mathrm{n}}_{\mathrm{h}}$, Mobility of conduction electrons is ${\mathrm{m}}_{\mathrm{e}}$and Mobility of holes is ${\mathrm{m}}_{\mathrm{h}},$ will be

1.  $\mathrm{e}\left[{\mathrm{n}}_{\mathrm{e}}{\mathrm{m}}_{\mathrm{h}}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{n}}_{\mathrm{e}}{\mathrm{m}}_{\mathrm{e}}\right]<mspace\; width="1em"></mspace>$

2.  $\mathrm{e}\left[{\mathrm{n}}_{\mathrm{e}}{\mathrm{m}}_{\mathrm{e}}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{n}}_{\mathrm{h}}{\mathrm{m}}_{\mathrm{e}}\right]<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>$

3.  ${\mathrm{en}}_{\mathrm{e}}\left[{\mathrm{m}}_{\mathrm{e}}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{m}}_{\mathrm{h}}\right]<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>$

4.  $\mathrm{e}\left[{\mathrm{n}}_{\mathrm{e}}{\mathrm{m}}_{\mathrm{e}}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{n}}_{\mathrm{h}}{\mathrm{m}}_{\mathrm{h}}\right]<mspace\; width="1em"></mspace>$

A semiconductor is known to have an electron concentration of \(8\times 10^{13}~\text{cm}^{-3},\) and a hole concentration of \(5\times 10^{2}~\text{cm}^{-3}.\) The semiconductor is: