Question

Which of the given statements are correct regarding unbiased $p$ - $n$ junction?
I. Drift and diffusion currents occur $p$ to $n$-side.
II. Initially, diffusion current is large and drift current is small.
III. Finally, diffusion and drift currents grow to be equal in magnitude.
IV. Under equilibrium there is no net current across $p-n$ junction plane.

• A. I and IV
• B. I, II and III
• C. II, III and IV
• D. All of these

Answer 1

Answer: (C)

Initially, diffusion current is large and drift current is small. As the diffusion process continues, the space-charge regions on either side of the junction extend, thus increasing the electric field strength and hence drift current.
This process continues until the diffusion current equals the drift current. Thus, a $p-n$ junction is formed. In a $p-n$ junction under equilibrium there is no net current.