Question

In PN junction, if P side is highly doped and N side is lightly doped, then

• A. depletion layer has more region in P side
• B. depletion layer has more region in N side
• C. depletion layer has equal region in both side
• D. there will be no depletion layer

Hint:

Depletion region width is inversely proportional to doping concentration: \[ W \propto \frac{1}{\text{doping}} \] Lightly doped side always has wider depletion region.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In a PN junction, the depletion region is formed due to the diffusion of charge carriers across the junction.
To maintain electrical neutrality, the total uncompensated charge on both sides must be equal.
Step 2: Key Formula or Approach:
The charge neutrality condition is $N_A \cdot W_P = N_D \cdot W_N$.
Here, $N_A$ and $N_D$ are the doping concentrations, and $W_P$ and $W_N$ are the widths of the depletion layer in the P and N regions respectively.
Step 3: Detailed Explanation:
Since $N_A \cdot W_P = N_D \cdot W_N$, we can deduce that the width of the depletion layer is inversely proportional to the doping concentration ($W \propto \frac{1}{N}$).
Given that the P-side is highly doped ($N_A$ is large) and the N-side is lightly doped ($N_D$ is small), it implies $W_N>W_P$.
Therefore, the depletion layer extends further, or has more region, into the lightly doped N-side.
Step 4: Final Answer:
The depletion layer has more region in N side.