Free Basic Electronics Solid State by B.L Theraja Notes

Basic Electronics Semiconductor —
I
•
Materials that permit flow of electrons are called conductors (e.g., gold, silver, copper, etc.).
•
Materials that block flow of electrons are called insulators (e.g., rubber, glass, Teflon, mica, etc.).
•
Materials whose conductivity falls between those of conductors and insulators are called semiconductors. •
Semiconductors are “
part
-
time
”
conductors whose conductivity can be controlled.
germanium
Semiconductors
silicon
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II
•
Silicon is the most common material used to build semiconductor devices. •
Si is the main ingredient of sand and it is estimated that a cub
ic mile of seawater contains 15,000 tons of Si. •
Si is spun and grown into a crystalline structure and cut into w
afers to make electronic devices.
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III
•
Atoms in a pure silicon wafer contains four electrons in outer o
rbit (called valence electrons).
–
Germanium is another semiconductor material with four valence el
ectrons.
•
In the crystalline lattice structure of Si, the valence electron
s of every Si atom are locked up in covalent bonds with the valence electrons of four n
eighboring Si atoms. –
In pure form, Si wafer does not contain any free charge carriers
. –
An applied voltage across pure Si wafer does not yield electron flow through the wafer. –
A pure Si wafer is said to act as an insulator. •
In order to make useful semiconductor devices, materials such as
phosphorus (P) and boron (B) are added to Si to change Si
’
s
conductivity.
4 valence electrons
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