A diode is made by joining P-type and N-type materials.
The junction of a diode is the region where the P-type material ends and the N-type material begin.
2.) Depletion Region
At the instant when junction is formed, diffusion takes place. That is some holes will move from the P-type material intro the N-type material.
Likewise some electron will move from the N-type material into the P-type materials.
These holes and free electrons, which moves across the junction, recombine and produces a depletion region at the junction.
The depletion region is where there is no mobile majority charge carrier.
It contains positively and negatively charge atoms on either sides of the junction.
3.) Barrier Potential Difference (or Barrier Voltage)
The opposite charge that build up on each side of the junction create a barrier voltage or potential barrier which resist any further free electrons and holes from cross the junction.
The barrier voltage is about 0.3V for a Germanium junction and 0.7V for a Silicon junction.
4.) Reverse Bias
When P-type material is connected to the negative terminal of the supply and the N-type material is connected to the positive terminal of the supply, the diode is said to be reverse biased.
The external voltage supply causes the majority carriers:
- Holes from P-type material
- Electrons from N-type material
To move away from the junction: As a result. the depletion region at the junction becomes larger and wider.
5.) Diode Reverse and Forward Bias Characteristics Curve
Where the diode is reversed-bias, a very small current (due to the minority carrier) called the reverse current or leakage current will flow only.
This means that, the reverse biased resistance of the diode is very high.
When the reverse bias voltage is high enough, it will cause damage or breakdown at the PN junction. this reverse voltage is called the breakdown voltage.
For any diode, the Peak Inverse Voltage (PIV) is the maximum safe reverse voltage of a diode specified by the manufacturer.
When the P-type material is connected to the positive terminal of the supply and the N-type material is connected to the negative terminal of the supply, the diode is said to be forward biased.
The potential of the external supply forces:
- Holes from P-type material
- Electrons from N-type material to cross the junction
A large current called the forward current flow through the diode.
7.) Diode forward Bias Characteristic Curve
When the amount of forward bias voltage equals the barrier voltage, there is no longer any depletion region and the junction can conduct current.
This barrier potential difference, VF is 0.3V for Germanium diode and 0.7V for Silicon diode.
8.) Characteristic of a diode
The anode is the P-type material of the diode. The cathode is the N-type material of the diode.
A diode is a non-linear device. When it is forward biased, current can flow through it easily since it acts a very low resistance.
When the diode is forward biased, it acts as a closed switch in series with a small forward voltage. (0.7V for Silicon)
When it is reverse biased, current does not flow through it since it now acts as a very high resistance.
When the diode is reverse biased, it acts as an open switch.
There will be a continuation about this topic next week! A more elaborate explanation for better understanding. I will be also adding some examples.
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