Zener diode: This is designed to operate in the reverse breakdown voltage region continuously without being damaged.

Application of Zener diode: It is used as a voltage regulator

Photo diode: This is an opto electronic device in which light rays are used for excitation.

Application of photo diode: It is used in photo detection and demodulation of optical signals. It is also used in optical communication equipments and logic circuits.

Light emitting diode: This converts electrical energy into light energy under forward bias condition. This is a photo electronic device.

Application of LED:In burglar alarm systems, infrared LEDs are used. It is also used in calculators and digital watches for numeric displays.

Solar cell: This converts solar energy into electrical energy.

Application of LED: They are used in power traffic signals and remote radio telephones.