#### Answer

$σ = 16,000 (Ω-m)^{-1} $

#### Work Step by Step

Given:
Germanium to which $ 10 ^{24} m^{-3}$ As atoms have been added is an extrinsic semiconductor at room temperature, and virtually all the As atoms may be thought of as being ionized (i.e., one charge carrier exists for each As atom).
Required:
electrical conductivity of this material, assuming electron and hole mobilities of 0.1 and 0.05 $m^{2}/V-s$, respectively
Solution:
The material is n-type extrinsic; thus, Equation 18.16 is applicable using $n = 10 ^{24} m^{-3}$:
$σ = n|e|μ_{e} = (10 ^{24} m^{-3})(1.6 \times 10^{-19} C)( 0.1 m^{2}/V-s)= 16,000 (Ω-m)^{-1} $