by Martin White

Created on: November 11, 2009   Last Updated: November 13, 2009

A diode is a two terminal device which allows the current to flow only in one direction. The mechanism is that it works like a switch. When the current passes through it in the right manner it acts as a closed switch and when the current passes through it in the wrong way or in the opposite direction, it acts as an open switch; i.e. not shorted or connected. It is also said to conduct current asymmetrically or unidirectional, that is, it conducts current more easily in one direction than in the opposite direction.

The diode is also known as semiconductor diode because it is made of semiconductor materials like silicon and germanium. But silicon or germanium are not used purely in the manufacturing of diode. Instead, these materials are doped with impurities to make the diode conduct electricity in one direction and oppose in other direction. When the diode conducts current, it is called to have in forward direction and when it does not conduct current it is said to have in reverse direction. Therefore, a diode is also thought of as a check valve. Thermionic diodes are thermionic values. These are actually electrodes surrounded by vacuum in glass case.

But in today's modern world most diodes are made of semiconductor materials. But, as also told above, semiconductors are not used purely in their original form but they are added with impurities with elements of third or fifth group. These additions of impurities make the diode to work in the manner we want. This basically gives a more control over the flow of electrons and its current voltage characteristics are very suitable for us. Giving diode a voltage results in the increase of diode voltage up to a specific point.

But, after that point, the diode voltage does not increase. Instead, its current keeps on increasing and the diode enters in the ohmic region. This behavior is due to the depletion region which exists when the two types of semiconductor materials are joined together. These two types are called as p type and n type semiconductor. When an element having three electrons in its orbit is joined with the silicon or germanium atom is a p-type semiconductor because there is a hole in the system. Similarly when an element having five electrons in its orbit is joined or bonded with silicon or germanium, it is an n-type material. When p type and n type material are joined together a junction is created which creates a layer known as depletion layer.

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