Question

Consider an unbiased $p-n$ junction with potential barrier $\text{b volts}$. Now suppose the $p-n$ junction is forward biased with a battery having potential difference $V\text{volts}$. It is given that $V<\text{b}$. Then choose the correct option.

• A. The potential barrier after biasing will be less than $\text{b}$ and $n-$ side has higher potential
• B. The potential barrier after biasing will be less than $\text{b}$ and $p-$ side has higher potential.
• C. The potential barrier after biasing will be greater than $\text{b}$ and $n-$ side has higher potential
• D. The potential barrier after biasing will be greater than $\text{b}$ and $p-$ side has higher potential.

Answer 1

The correct option is A The potential barrier after biasing will be less than $\text{b}$ and $n-$ side has higher potential

Before biasing, the depleted region and potential barrier can be represented as shown below.

In this case, the $n-$ side is at higher potential.


After forward biasing, the depletion region and potential barrier both decreases, as the potential of $p-$ side is increased due to the battery

Given that, $V<\text{b}$, therefore, the potential difference between $p-$ side and $n-$ side is given by,

${\text{b}}^{\prime }=\text{b}-V$

$\Rightarrow {\text{b}}^{\prime }<\text{b}$

In this case, the depletion region and the potential barrier are represented as


The $n-$ side will still have higher potential, as the voltage of battery $V$ is less than $\text{b}$.

Hence, option $\left(\text{A}\right)$ is correct.

Why this question? Note: In forward biasing the $p-n$ junction, both the potential barrier and the width of the depletion region decreases and the direction of net current will be from $p-$ side to $n-$ side.