The dominant mechanisms for motion of charge carriers in forward and reverse biased silicon p-n junctiona are
1. Drift in both forward and reverse bias
2. Diffusion in both forward and reverse bias
3. Diffusion in forward bias and drift in reverse bias
4.Drift in forward bias and diffusion in reverse bias
 
Please explain reason as well

Asked by rajeshtitu | 14th Jul, 2016, 09:09: PM

Expert Answer:

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.

Answered by Romal Bhansali | 15th Jul, 2016, 11:30: AM