Rectifier diode

A diode rectifier is a semiconductor device and comes under 'active' electronic components. Its basic function is to allow the passage of electric current only in one direction and block from the other. This property also results in rectification of electric current when an AC source is used. A rectifier diode is generally recognised by its black colour and a white ring at one of its ends, something comparable to the resistor colour coding we studied in a previous article. Its size may differ with its power handling capacity. Its two ends are with two leads or terminals and hence the name diode (meaning two-legged in Greek).
A diode like all semiconductors is basically made up of pure silicon (more popular nowadays than germanium). By nature silicon is a bad conductor of electricity therefore by mixing certain impurities into it(doping), conductivity to an extent is achieved. These impurities can be positive carriers or negative carriers of charge known as p-type and n-type respectively.

In a diode the p-type and n-type silicon are fused together to form a junction called pn junction. When connected to a voltage source, this junction will restrict the flow of current from n-type to p-type and will allow the flow of current from p-type to n-type silicon, only if the voltage is more than 0.6 volts. This minimum voltage is required in any silicon semiconductor to initiate the conduction of electrons and is known as the forward-voltage. The p-type terminal of a diode is called the anode and the n-type terminal is called the cathode and is indicated by a ring or band on its body.