DIODES

Definition: 

A diode is a semiconductor device which conducts electricity only on a particular direction.

What makes up a diode:

A diode is made up of 1  positive and 1 negative region which together forms a P-N Junction.this is called P-N Junction diode.

Where it's used:

diodes are used to rectify ac current,reverse voltage protection etc.

Rectifiers:

rectifiers are simply divided into three types,the half bridge rectifier, full bridge rectifier and bridge rectifier.

Types of diodes:

scottky diodes,zener diodes,light emitting diodes, photodiodes, thyristor etc are different kinds of diodes. 

simple diode

zener diode

thyristor

light emmiting diode