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The barrier voltage (V0 or Vr) in a junction diode is the effect of
Due to the density gradient across the junction, holes will initially diffuse to the right across the junction, and electrons to the left. The positive holes which neutralizes the acceptor ions near the junction in the p-type silicon disappears as a result of combination with electrons which have diffused across the junction. Similarly, electrons in n-type semiconductor combines with holes.
In a zener diode large reverse current is due to
The large reverse current flow in zener diode is due to rupturing-off or tearing-off of covalent bends within the depletion layer. This phenomena is called zener breakdown phenomena, It is due to large electric field intensity.
For thermionic emission
The work function of a metal represents the minimum amount of energy that must be given to the fastest-moving electron at the absolute zero of temperature in order for this electron to be able to escape from the metal. Hence, low work function (Ew) is required for thermionic emission.
The most commonly used type of electron emission in electron tubes is
When forward bias is applied to a junction diode, it
Width of depletion layer,
Hence, when forward bias is applied to a p-n junction diode, width of the depletion layer is reduced i.e. potential barrier is decreased
The emission of electrons in a vacuum diode is achieved by
The main reason why electrons can tunnel through a p-n junction is that
In a p-n junction tunnel diode, the depletion layer width is negligible and therefore, the charge carriers will be penetrating the depletion layer almost at the speed of light and this property is called tunnelling of charge carriers across the junction.
The forbidden energy gap in semiconductors
The energy level diagram for a semiconductor is shown below.
EG is called “band gap” or "forbidden energy gap” which lies between the valence band and the conduction band.
The barrier potential for a Ge p-n junction is
Typical value of “Barrier voltage” or "Contact potential” for a p-n junction is:
V0 = 0.2 V (for Ge p-n junction diode)
= 0.7V (for Si p-n junction diode)
With the increase in temperature, the resistivity of an intrinsic semiconductor decreases. This is because, with the increase of temperature
In an intrinsic semiconductor, as the temperature increases mobility is slightly reduced since mobility of charge carrier is inversely proportional to temperature. This will slightly reduce the conductivity. But, due to temperature effect, large number of covalent bonds are broken which creates electrons and holes and this increases the conductivity by a larger value. As a result of this resistivity is decreased