What is the difference between Diffusion current and Drift current?

Hint: Drift current arises due to the motion of charge carriers under an applied electric field, whereas diffusion current results from charge carriers moving from areas of high concentration to low concentration due to a concentration gradient.

Complete Explanation:

Drift Current

1. Drift current occurs when charge carriers (electrons and holes) move in response to an external electric field.
2. In a drift current, positive charge carriers (holes) move along the direction of the electric field, while negative charge carriers (electrons) move in the opposite direction.
3. The movement of charge carriers generates a current in the same direction as the electric field.
4. The drift velocity of charge carriers increases as the electric field strength increases, which also defines the carriers’ mobility.
5. Drift current follows Ohm’s law and depends on the strength of the electric field and the concentration of charge carriers.

Diffusion Current

1. Diffusion current arises from the movement of charge carriers from regions of higher concentration to regions of lower concentration.
2. When a semiconductor has a non-uniform doping level, a concentration gradient of charge carriers forms, causing diffusion.
3. This diffusion process naturally occurs to balance carrier distribution, generating a diffusion current. No external electric field is required; the current is driven by the repulsive forces between like-charged carriers in high concentration areas.
4. As carriers spread out due to these forces, their concentration changes, eventually leading to a uniform distribution.
5. The direction of diffusion current is determined by the concentration gradient, typically moving from areas of high electron concentration or low hole concentration.

Note:

The diffusion current is proportional to the carrier concentration gradient, reflecting the initial non-uniformity in carrier distribution. For diffusion current, holes flow in the direction of current, while electrons flow in the opposite direction.