Question

The variation of electron concentration in the space-charge region of p-n junction diode under equilibrium is shown below:


The magnitude of electron diffusion current density $J_{no}$ at x=0 will be

(Assume, effective diffusion coefficient of electrons $D_n=6c{m}^2/sec$).

• A. $9\times {10}^{3}A/c{m}^2$
• B. $12.50\times {10}^{3}A/c{m}^2$
• C. $7.68\times {10}^{3}A/c{m}^2$
• D. $8.50\times {10}^{3}A.c{m}^2$

Answer 1

The correct option is C $7.68\times {10}^{3}A/c{m}^2$

Given, space-charge width
$W=1.25\mu m=1.25\times {10}^{-4}cm$
Electron diffusion current density $J_{nD}=q{D}_n\frac{dn}{dx}$
where concentration gradient, $\frac{dn}{dx}=\frac{n_{no}-n_{po}}{W}$
$\frac{dn}{dx}=\frac{{10}^{18}-2\times {10}^2}{1.25\times {10}^{-4}}c{m}^{-4}=8\times {10}^{21}c{m}^{-4}$
$J_{nD}=1.6\times {10}^{-19}\times 6\times 8\times {10}^{21}A/c{m}^2$
$J_{nD}=7.68\times {10}^{3}A/c{m}^2$