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Difference Between Drift Current and Diffusion Current

What is the drift current?

At normal temperatures, when the voltage is applied by connecting the ends of a conductor or semiconductor to battery's terminal, a strong electric field is generated inside the conductor or semiconductor, Due to this strong electric field free-electron experience, a force opposite to the electric field's direction and starts moving towards the positive terminal of the battery. 

this moving electron towards the battery's positive terminal collide with the atoms of the conductor or semiconductor, changing their direction of movement, but due to the external field, they move in a straight line toward the battery's positive terminal. 

Due to this electron movement, an electric current flows inside the conductor or semiconductor. Since this current flows due to drifting of the electron, it is called drift current. The speed at which electrons move is called Drift Velocity. The direction of current flowing in a semiconductor or conductor is always opposite to the direction of electrons moving.

What is the diffusion current?

In general, it has been observed that the flow of electrical current in any conductor is due to free electrons. When a potential difference is to apply between the ends of the conductor, the free electrons present in the conductor pass through the negative terminal of the battery and move through the driver towards the positive terminal of the battery. 

Which is called Drift Current. This process occurs only at the normal temperature in the conductor or semiconductor. But in addition to the drift current in an impure semiconductor (P-Type or N-Type), another current also flows.

Which is called Diffusion Current. Diffusion in an impure semiconductor is caused by the transport of charge carriers (holes). The action of transport of charge is called Diffusion.
Why does Diffusion occur in impure semiconductors?

To understand the process of diffusion, let us take an example. For this, We will take P-Type semiconductors. Inside this semiconductor, the distribution of holes and electrons is uneven rather than uniform.

The number of positively charged holes on one end of the semiconductor is very high and less on the other end. Holes on the end of the semiconductor, where the number of holes is very high, start experiencing a repulsive force due to another hole and try to move into an area where the number of holes is less.

In this way, the process of moving from a high-hole region of charge to a low-hole region is called Diffusion and the current flowing due to movement of the hole is called Diffusion Current.
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