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Introduction:

In n-type semiconductor, the electrons are majority charge carries while holes are minority charge carriers. In p-type, the holes are majority charge carriers and electrons are minority charge carriers. These two types of materials namely n-type and p-type are chemically combined with a special fabrication technique to form a pn junction diode animation.
P-n Junction Diode

(Source : Wikipedia)

The pn junction forms a popular semiconductor devices called pn junction diode. The pn junction animation has two terminals called electrodes, one each from p-region and n-region. Due to the two electrodes it is called diode i.e di + electrode.

To connect the n and p-regions to the external terminals, a metal is applied to the heavily doped n and p-type semiconductor regions. Such a contact between a metal and a heavily doped semiconductor is called ohmic contact. Such an ohmic contact has two important properties,

* It conducts current equally in both the directions.
* The drop across the contact is very small, which do not affect the performance of the devices.

Biasing of P-n Junction Diode

Applying external d.c voltage to any electronic devices is called biasing. As seen, there is no current in the unbiased p-n junction diode animation at equilibrium.

Key Point:

The usefulness of pn junction diode animation lies in the fact that it allows current flow only in one direction, under biased condition.

Depending upon the polarity of the d.c voltage externally applied to it, the biasing is classified as forward biasing and reverse biasing.
Types of Diodes

When forward current flows under forward biasing, diode gets heated. Hence forward current should not exceed the particular maximum value. Similarly the diode can be damaged due to large reverse voltage applied to it during reverse biasing.