Semiconductors PPT 1

Conduct electricity well
  These include metals, electrolytes, plasma ...
The most used conductors are Au, Ag, Cu, Al, Fe ...

Practically do not conduct electric current.
  These include plastics, rubber, glass, porcelain, dry wood, paper ..

They occupy an intermediate position between conductors and dielectrics.
Si, Ge, Se, In, As

Introduction

Semiconductors are materials whose electrical properties lie between Conductors and Insulators.
Ex : Silicon and Germanium

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Periodic Table

This abridged table contains elements with three to five valence electrons, with Si being the most important.

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Silicon

Si has four valence electrons. Therefore, it can form covalent bonds with four of its neighbors.
When temperature goes up, electrons in the covalent bond can become free.

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Electron-Hole Pair Interaction

With free electrons breaking off covalent bonds, holes are generated.
Holes can be filled by absorbing other free electrons, so effectively there is a flow of charge carriers.

Semiconductors are classified in to P-type and N-type semiconductor
P-type: A P-type material is one in which holes are majority carriers i.e. they are positively charged materials (++++)
N-type: A N-type material is one in which electrons are majority charge carriers i.e. they are negatively charged materials (-----)

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Doping (N type)

Pure Si can be doped with other elements to change its electrical properties.
For example, if Si is doped with P (phosphorous), then it has more electrons, or becomes type N (electron).

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Doping (P type)

If Si is doped with B (boron), then it has more holes, or becomes type P.

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Summary of Charge Carriers

What are P-type and N-type ?

Semiconductors are classified in to P-type and N-type semiconductor
P-type: A P-type material is one in which holes are majority carriers i.e. they are positively charged materials (++++)
N-type: A N-type material is one in which electrons are majority charge carriers i.e. they are negatively charged materials (-----)

Diodes

Electronic devices created by bringing together a p-type and n-type region within the same semiconductor lattice. Used for rectifiers, LED etc

Diodes

It is represented by the following symbol, where the arrow indicates the direction of positive current flow.

Forward Bias and Reverse Bias

Forward Bias : Connect positive of the Diode to positive of supply…negative of Diode to negative of supply
Reverse Bias: Connect positive of the Diode to negative of supply…negative of diode to positive of supply.

Characteristics of Diode

Diode always conducts in one direction.
Diodes always conduct current when “Forward Biased” ( Zero resistance)
Diodes do not conduct when Reverse Biased
(Infinite resistance)