The PN Junction Diode

The P‒N Junction Diode

• The p‒n junction forms a popular semiconductor device called p‒n junction diode.

• The p‒n junction 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 semiconductor is called ohmic contact.

• Such an ohmic contact has two important properties,

1. It conducts current equally in both the directions.

2. The drop across the contact is very small, which do not affect the performance of the device.

• Fig. 2.4.1 (a) shows schematic arrangement of p‒n junction diode while Fig. 2.4.1 (b) shows the symbol of p‒n junction diode.

• The p‒region acts as anode while the n‒region acts as cathode. The arrowhead in the symbol indicates the direction of the conventional current, which can flow when an external voltage is connected in a specific manner across the diode.

• Applying external d.c. voltage to any electronic device is called biasing.

• The usefulness of p‒n junction 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.

Review Questions

1. Draw the symbol of p‒n junction diode. What are ohmic contacts ?

2. What is biasing of p‒n junction diode ?

3. Discuss the construction of p‒n junction diode.