Consider that the concentration of electrons in a semiconductor bar varies linearly from $2 \times 10^{17} \mathrm{~cm}^{-3}$ at $x=1 \mu \mathrm{~m}$ to $1 \times 10^{16} \mathrm{~cm}^{-3}$ at $x=4 \mu \mathrm{~m}$ along the $x$-direction. Assume that the concentration of electrons is not varying along other directions (that is along $y$ - and $z$-directions).
[Given: the mobility of electron is $1400 \mathrm{~cm}^{2} \mathrm{~V}^{-1} \mathrm{~s}^{-1}$, thermal voltage is $25 ~\text{mV}$ and electronic charge is $1.6 \times 10^{-19}$ Coulomb.]
The density of electron diffusion current (in $\mathrm{A} / \mathrm{mm}^{2}$ ) is $\_\_\_\_$.
(rounded off to two decimal places)
