Question

The dominant mechanisms of motion of change carriers in forward and reverse biased silicon $P-N$ junction are

• A. drift in forward bias, diffusion in reverse bias
• B. diffusion in forward bias, drift in reverses bias
• C. diffusion in both forward and reverse bias
• D. drift in both forward and reverse bias

Answer 1

Answer: (B)

diffusion in forward bias, drift in reverses bias

In forward bias we apply voltage in a direction opposite to that of the barrier potential. Now, we know that the p-side of the diode is connected to the positive terminal and the n-side of the diode is connected to the negative terminal of the battery.

So, the electrons in the n-side and the holes in the p-side get pushed towards the junction. This results in increased diffusion of electrons from n-side to p-side region and the increased diffusion of holes from p-side to n-side region. Hence, dominant mechanism in forward bias is due to diffusion.

In reverse bias, the n-side of the diode is connected to the positive terminal and the p-side is connected to the negative terminal.

So, the electrons in the n-side and the holes in the p-side get pushed away from the junction. This results in zero diffusion current. Hence, dominant mechanism in reverse bias is due to drift.

So, the correct answer is option 3.