Question

The depletion layer in the $p-n$ junction region is caused by

• A. drift of holes
• B. diffusion of charge carriers
• C. migration of impurity ions
• D. drift of electrons

Answer 1

Answer: (B)

diffusion of charge carriers

Answer 2

When a $p$ - $n$ junction is formed, some of the free electrons in the $n$ region diffuses across the junction and combine with holes to form negative ions. In doing so they leave behind positive ions at the donor impurity sites. Similarly, holes from p side diffuse to the $n$ side and thus form a layer called diffusion layer at the junction. So the depletion region is caused by the diffusion of charge carriers.