Question

What is the number density of donor atoms which must be added to a pure germanium semiconductor to produce an N-type semiconductor of conductivity $6.4X{10}^{2}oh{m}^{-1}{m}^{-1}$? The mobility of electrons in N-type germanium is $4X{10}^{-1}{m}^2{V}^{-1}{s}^{-1}$. Neglect contribution of holes to conductivity.

• A. ${10}^{20}{m}^{-3}$
• B. ${10}^{21}{m}^{-3}$
• C. ${10}^{22}{m}^{-3}$
• D. ${10}^{23}{m}^{-3}$

Answer 1

The correct option is C ${10}^{22}{m}^{-3}$

$6={\eta }_e\times e\times \mu$

$\Rightarrow 6.4\times {10}^2={\eta }_e\times 1.6\times {10}^{-19}\times 4\times {10}^{-1}$

$\Rightarrow {\eta }_e={10}^{22}{m}^{-3}$