In condensed matter physics and electrochemistry, drift current is the electric current, or movement of charge carriers, which is due to the applied electric field, often stated as the electromotive force over a given distance.
When an electric field is applied across a semiconductor material, a current is produced due to the flow of charge carriers.
The term is most commonly used in the context of electrons and holes in semiconductors, although the same concept also applies to metals, electrolytes, and so on.
Electrons, being negatively charged, get pushed in the opposite direction to the electric field, while holes get pushed in the same direction as the electric field, but the resulting conventional current points in the same direction as the electric field in both cases.
If an electric field is applied to an electron in a vacuum, the electron will accelerate faster and faster, in approximately a straight line.
Typically, electrons are moving randomly in all directions (Brownian motion), frequently changing direction when they collide with grain boundaries or other disturbances.
Between collisions, the electric field subtly accelerates them in one direction.
The amount of drift current depends on the concentration of charge carriers and their mobility in the material or medium.
Drift current frequently occurs at the same time as diffusion current; the following table compares the two forms of current: In a p-n junction diode, electrons and holes are the minority charge carriers in the p-region and the n-region, respectively.
In an unbiased junction, due to the diffusion of charge carriers, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current.
[1] The drift current in an unbiased junction is caused by the field formed due to the redistribution of charge carriers, the ionised donor and acceptor atoms additional electrons and holes are lost from diffusion, hence leaving positive and negative ions.
These ions in the crystal lattice result in a charge disparity, creating a built in electric field.
But as minority charge carriers can be thermally generated, drift current is temperature dependent.
When an electric field is applied across the semiconductor material, the charge carriers attain a certain drift velocity .
Drift current density due to the charge carriers such as free electrons and holes is the current passing through a square centimeter area perpendicular to the direction of flow.