P-N Junction Diode
P-N Junction Diode is form by doping one side of a piece of silicon with a P-type dopant (Boron) and the other side with a N-type dopant (phosphorus). This diode is simply a two-terminal device which allows the current to flow in one direction only.
We can use any Ge semiconductor instead of Silicon. PN junction diodes work differently under different biasing conditions. We will study this one by one.
Zero Biased Condition
As the name suggests there is no biasing to P-N junction diode. That simply means no external voltage source is present. Thus under zero biasing condition, electrons (majority carrier in N-type) diffuse to the P-side and at the same time holes (majority carrier in P-type) diffuse towards the N-side through the junction and then combine with each other.
This carrier combination leads to the generation of an electric field but the generated electric field restricts further diffusion of charged carriers so that there is no movement in the middle region. The name of region is Depletion width or Depletion region or Space charge.
Forward Biased Condition
In the forward bias condition, P-Type material is in connect to the positive terminal of the battery and N-type material is in connect to the negative terminal of the battery. In forward biasing we are giving positive voltage to the diode.
Electrons (majority carrier in N-type) from the N-region cross the junction or depletion region and enter the P-region. Due to positive voltage, electrons get attracted towards the positive terminal. At the same time the holes are attracted to the negative terminal of the battery. In this condition, the width of the depletion region decreases due to the reduction in the number of positive and negative ions. However, a large current flows through the junction.
Reverse Biased Condition
In the reverse bias condition, P-Type material is in connect to the negative terminal of the battery and N-type material is in connect to the positive terminal of the battery. In reverse biasing we are giving negative voltage to the diode.
The positive voltage applied to the N-type material attracts electrons towards the positive electrode and away from the junction. While the holes in the P-type end are also attracted away from the junction towards the negative electrode.
This results in a wider depletion layer due to a lack of electrons and holes. This exhibiting a high impedance path. Thus a large potential barrier exists. This barrier also prevents the current from flowing through the semiconductor material. However, a very small leakage current does flow through the junction.
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