VALANCE SATURATION
- WE
- Jul 24, 2017
- 2 min read
Each atom in a silicon crystal has eight electrons in its valance orbit.These eight electron produce a chemical stability that results in a solid piece of silicon material.When eight electrons do not exist naturally in an element there seems to be a tendency for the element to combine and share electrons with other atoms so as to have 8 electrons in the outer orbit.
There are advanced equations in physics that partially explain why eight electrons produce chemical stability in different materuials but no one knows the reasons why the no. 8 is so special.It is one of those laws like the law of gravity,Coulomb’s law and other laws that we observe but can not fully explain.
When the valance orbit has 8 electrons,it is saturated because no more elecrons can fit into this orbit.Stated as a law,
Valance saturation: n=8
In words,the valance orbit can hold no more than 8 electrons.Furthermore, the 8 valance electrons are called bound electrons because they are tightly held by the atoms.Because of the bound electrons, a silicon crystals is almost a perfect insulator at room temperature,approx. 25â—¦c.
THE HOLE : The ambient temperature is the temperature of the surrounding air.When the ambient temperature is above absolute zero the heat energy in this air causes the atoms in a silicon crystals to vibrate.The higher the temp the stronger the mechanical vibrations become.When you pick up a warm object the warmth you feel is the effect of the vibrating atoms.
In a silicon crystal the vibrations of the atoms can ocassionally dislodge an electron from the valance orbit.When this happens the released electron gains enough nergy to go into a larger orbit.In this larger orbit the electron is a free electron.
The departure of a electron creates a vacancy in the valance orbit called a hole .This hole behaves like a positive charge because the loss of a electron produces a (+) ion.The hole will attract and capture any electron in the immediate vicinity.The existence of hole is the critical difference b/w conductors and semi conductors.Holes enable semiconductor to do all kinds of things that are impossible with conductors.
At room temp thermal energy produces only few holes and free electrons.To increase the no. of holes and free electrons, it is necessary to dope the crystals.
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