p-n junction
‘p-n junction (diode)’ is a single semi conducting crystal with one of its end p-type & other end n-type material.
Whenever a p-n junction is formed in a crystal, following the diffusion process the electrons start entering into the p-type material. These electrons neutralize holes present closer to the junction. This leaves the positively charged immobile atoms in n-type region & negatively charged immobile atoms in p-type region, un-neutralised. These un-neutralised immobile charges present at both the sides of the junction, generate an electric field, which opposes the flow of electrons through the junction. But, still, those free electrons which have sufficiently large amount of energy to overcome this opposing force and cross the junction. This causes the increases in the immobile charged atoms & thereby increases the opposing electric field. This process continuous until even the most energetic electrons present in the n-type region, fails to overcome the opposing force & thereby fail to cross the junction. This brings the equilibrium state of the p-n junction.
Thus in equilibrium state in p-n junction diode we get
- A p-type material at one end, in which a large number of holes (majority charge carriers) are present.
- A n-type material at the other end, in which a large number of free electrons are present.
- A region across the junction on either side of the junction which contain only the immobile charges. There is no charge carrier present in the region. This region is called charge depletion region.
p-n junction and junction diode
(In Hindi + English mix Language)
The immobile charges present in the charge depletion region generate an opposing potential difference across the junction, which acts as a barrier for the majority charge carriers. This potential difference across the junction is known as junction potential barriers (VB or Vo)
[An unbiased diode has a depletion layer at the pn junction. The ions in this depletion layer produce a barrier potential. At room temperature, this barrier potential is approximately 0.7 V for a silicon diode and 0.3 V for a germanium diode.]
The value of VB (also known as height of junction potential barrier) and it depends upon the maximum energy of free electrons present in the n-type region. So its value depends upon the temperature of the material. Higher the temperature of the material more is the value of VB.
The width of the charge depletion region depends upon the doping concentration of the crystals. Higher the doping concentration lesser is the width of charge depletion region.