Coming to the types of currents in semiconductors, there are two terms need to be discussed. They are Diffusion Current and Drift Current.
Diffusion current
When doping is done, there occurs a difference in the concentration of electrons and holes. These electrons and holes tend to diffuse from higher concentration of charge density, to lower concentration level. As these are charge carriers, they constitute a current called diffusion current.
To know about this in detail, let us consider an N-type material and a P-type material.
· N-type material has electrons as majority carriers and few holes as minority carriers.
· P-type material has holes as majority carriers and few electrons as minority carriers.
If these two materials are brought too close to each other to join, then few electrons from valence band of N-type material, tend to move towards P-type material and few holes from valence band of P-type material, tend to move towards N-type material. The region between these two materials where this diffusion takes place, is called as Depletion region.
Hence, the current formed due to the diffusion of these electrons and holes, without the application of any kind of external energy, can be termed as Diffusion Current.
Drift Current
The current formed due to the drift (movement) of charged particles (electrons or holes) due to the applied electric field, is called as Drift Current. The following figure explains the drift current, whether how the applied electric field, makes the difference.
The amount of current flow depends upon the charge applied. The width of depletion region also gets affected, by this drift current. To make a component function in an active circuit, this drift current plays an important role.
