How does the diode work in an electronic circuit?

We would like to discuss one Element of an Electronic Circuit, the diode.

A diode is a two-terminal device that allows electric current to flow in only one direction. Thus, it is the electronic equivalent of a check valve or a one-way street. It is commonly used to convert  into the circuit Current.  It is made either of semiconductor diode or vacuum tube diode. Today, however, most high voltage  rectifier diodes are made from semiconductor material,especially silicon.

As mentioned earlier, there are two types of diodes: vacuum diodes and semiconductor diodes. A vacuum diode consists of two electrodes (cathode and anode) placed inside a sealed vacuum glass tube. A high voltage rectifier diode comprises p-type and n-type semiconductors. In hence, known as a p-n junction diode. It is usually made of silicon, but you can also use germanium or selenium.

So how the diode work in one circuit?

For Vacuum Diode

When the cathode is heated by a filament, an invisible cloud of electrons, called space charge, forms in the vacuum. Though electrons are emitted from the cathode, the negative space charge repels them. As electrons can’t reach the anode, no current flows through the circuit. However, when the anode is made positive, the space charge vanishes. As a result, current starts flowing from the cathode to the anode. Thus, electric current within the diode flows only from the cathode to the anode and never from the anode to the cathode.

 For P-N Junction Diode

A p-n junction diode comprises p-type and n-type semiconductors of silicon. The p-type semiconductor is usually doped with boron, leaving holes (positive charge) in it. The n-type semiconductor, on the other hand, is doped with antimony, adding a few extra electrons (negative charge) in it. So, electric current can flow through both semiconductors.

When you put p-type and n-type blocks together, the extra electrons from the n-type combine with the holes in the p-type, creating a depletion zone without any free electrons or holes. In short, current can no longer pass through the diode.

When you connect the battery’s negative terminal to the n-type silicon and the positive terminal to p-type (forward-bias), current starts to flow as electrons and holes can now move across the junction. However, if you reverse the terminals (reverse-bias), no current flows through the diode because holes and electrons are pushed away from each other, widening the depletion zone. So, just like a vacuum diode, a junction diode can also allow current to pass in one direction only.