What is the difference between Diffusion current and Drift current?

Diffusion Current:

Diffusion current arises due to the movement of charge carriers from a region of high concentration to a region of low concentration. This occurs naturally because particles tend to spread out uniformly. In semiconductors, if one side has a higher concentration of electrons or holes, they diffuse to the region of lower concentration, producing a diffusion current. For example, in a PN junction diode, electrons diffuse from the N-side (high electron concentration) to the P-side, and holes diffuse from the P-side to the N-side.

Drift Current:

Drift current, on the other hand, occurs when an external electric field is applied across the semiconductor. The electric field exerts a force on charge carriers, causing electrons to move opposite to the field direction and holes to move along the field direction. This organized movement of carriers results in a drift current.

Key Difference:

Diffusion current depends on the concentration gradient of carriers, while drift current depends on the applied electric field. In practical devices like diodes and transistors, both currents play crucial roles in overall conduction.