If a block of silicon is doped with a trivalent impurity and the other part with a pentavalent impurity , a boundry called the pn junction is formed between the resulting p-type and n-type portions and a basic diode is created.
A diode is a device that conducts current in only one direction. The pn junction is the feature that allows diodes, certain transistors, and other devices to work.
A p-type material consists of silicon atoms and trivalent impurity atoms such as boron. The boron atom adds a hole when it bonds with the silicon atoms. However, since the number of protons and the number of electrons are equal throughout the material , there is no net charge in the material and so it is neutral.
A n-type silicon material consists of silicon atoms and pentavalent impurity atoms such as antimony. As we know and impurity atoms releases an electron when it bonds with four silicon atoms, since there is still an equal number of protons and electrons throughout the material, there is no net charge in the material and so it is neutral.
PN Junction is Diodes:
If a piece of intrinsic silicon is doped so that part is n-type and the other part is p-type, a pn junction is forms at the boundary beteen the two regions and a diode is created.
The p region has many holes (majority carriers) from the impurity atoms and only a few thermally generated free electrons (minority carriers) . The n region has many free electrons from the impurity atoms and only a few thermally generated holes.
Water Analogy of Diodes
- When water pressure on left overcomes the restoring force of spring, the gate is opened and water is allowed to flow .
- When water pressure is from right to left, the gate is pressed against the solid stop and no water is allowed to flow.
- Spring restoring force is analogous to 0.6V needed to forward bias a Si diode.
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