Question

Two statements are given below:
A. When the forward bias voltage across a p-n junction diode increases above a certain threshold voltage, the diode current increases significantly.
B. This current is called reverse saturation current.
Choose the correct answer from the options given below:

• A. Statement A is true, but Statement B is false
• B. Both Statements A and B are true
• C. Both Statements A and B are false
• D. Statement A is false, but Statement B is true

Hint:

Forward Current is measured in milliamperes (mA) and is due to majority carriers. Reverse Saturation Current is measured in microamperes ($\mu$A) or nanoamperes (nA) and is due to minority carriers.

Answer 1

The Correct Option is A

Step 1: Understanding the Topic:
This question pertains to "Semiconductor Electronics," specifically the current-voltage (I-V) characteristics of a p-n junction diode. A diode is a non-ohmic device that acts as a one-way valve for current, and its behavior changes drastically depending on whether it is "forward-biased" or "reverse-biased."
Step 2: Key Formulas and Approach:
The diode current equation is $I = I_s (e^{V/\eta V_T} - 1)$.
Forward Bias: Applied voltage opposes the built-in potential barrier.
Reverse Bias: Applied voltage strengthens the potential barrier.

Step 3: Detailed Explanation:

Analysis of Statement A: In forward bias (p-side positive, n-side negative), the depletion region narrows. Initially, very little current flows. However, once the external voltage exceeds the "threshold voltage" (also called the knee voltage or cut-in voltage, $\approx 0.7 \text{ V}$ for silicon), the barrier is overcome and current rises exponentially. This statement is perfectly accurate. (True)
Analysis of Statement B: The significant current that flows in forward bias is called the "forward current," and it is caused by the movement of majority charge carriers. The term "reverse saturation current" specifically refers to the tiny current (on the scale of $\mu A$ or $nA$) that flows when the diode is reverse-biased, caused by minority carriers. Using this term to describe forward bias current is a categorical error. (False)
Since A is true and B is false, option (A) is the correct choice.
Step 4: Final Answer:
Statement A is true, but Statement B is false.