Question

When a p-n junction is reverse biased, the current becomes almost constant at $25\mu A$. When it is forward biased at $200meV$, a current of $75\mu A$ is obtained. Find the magnitude of diffusion current when the diode is (a) unbiased (b) reverse-biased at $200mV$ and (c) forward-biased at $200mV$.

Answer 1

Given,

p-n junction is reversed biased.

$i_1=25\mu A$

$V=200mA$

$i^2=75\mu A$

(a) unbiased condition.

Diffusion current=Drift current=$i_1$

$\therefore$ Diffusion Current$=25\mu A$

(b) Reversed biased condition at $200mV$

On the reverse biasing the diffusion current becomes zero.

(c) Forward biased condition at $200mV$

At,Forward biased, the actual current be $i$

So,

$i=$Drift Current$=$ Forward biasing current.

$i-i_1=i_2$

$\Rightarrow i-25\mu A=75\mu A$

$i=(75+25)\mu A=100\mu A$

$\therefore$ Diffusion current forward biasing becomes $100\mu A$ at $200mV$