What is the Difference Between Valence and Conduction Bands in semiconductors?

In summary, the conduction and valence bands are energy bands which are formed within an atom when many such atoms come close to each other. The topmost band which is completely filled with electrons is called the valence band. Above the valence band we have the conduction band (here electrons if exists are considered free to move when external electric field is applied. That is they are not bounded to any particular atom or atoms, they are termed as free electrons). When a pn junction conducts, the electrons from the conduction band falls in the holes of the valence band, the difference in energy is emmitted as light or many times heat.
  • #1
nst.john
163
1
I am learning the basic make-up of LED's and they mentioned conduction and valence bands. What I am unsure of is which of these bands are either the p-type or n-type materials within the LED/semiconductor, and/or which band is positive with holes or negative with the free electrons. Can I just get a simple definition of what is in each band and what they mean?

Thank You!
 
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  • #2
Each atom consists of bounded electrons in discrete energy levels (The electrons don't have continuous variation in energy when bounded to a single atom). when many such atoms come close to each other, the discrete energy levels now become energy bands. Within one band electron can have continuous variation of its energy. Many such band levels are formed. The topmost band which is completely filled with electrons is called valence band. Above valance band we have conduction band (here electrons if exists are considered free to move when external electric field is applied. That is they are not bounded to any particular atom or atoms, they are termed as free electrons).
In LEDs (or simply Diode for time being) We have P type semiconductor and n type semiconductor joined by some process to form a pn junction. The valence band of p type is electron deficient so rich in holes. And the conduction band of n type is rich in electons. When pn juction conducts, the electrons from n type conduction band falls in holes of p type valence band, the difference in energy is emmitted as light or many times heat.
 
  • #3
nst.john said:
I am learning the basic make-up of LED's and they mentioned conduction and valence bands. What I am unsure of is which of these bands are either the p-type or n-type materials within the LED/semiconductor, and/or which band is positive with holes or negative with the free electrons. Can I just get a simple definition of what is in each band and what they mean?

Thank You!

I'm unsure what the exact problem is here. What about the simplest and most obvious description here:

If the doping level is closer to the conduction band than the valence band, it is a n-type. Dominant charge carrier are electrons.
If the doping level is closer to the valence band than the conduction band, it is p-type. Dominant charge carrier are holes.

I'm guessing this description is provided in the material that you are learning. So where in here exactly did you not understand?

Zz.
 
  • #4
Well I am really teaching myself and got confused and my teacher was unsure as well so I checked here. This was all I needed and my question has been answered! Thank you!
 
  • #5
nst.john said:
Well I am really teaching myself and got confused and my teacher was unsure as well so I checked here. This was all I needed and my question has been answered! Thank you!

May I suggest that, if by now you still haven't been told of it, you check out the Hyperphysics website? It has a very clear description that would have answered your question:

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html

This goes for other topics as well.

Zz.
 

FAQ: What is the Difference Between Valence and Conduction Bands in semiconductors?

What is the Difference Between Valence and Conduction Bands in semiconductors?

The valence band and conduction band are two energy levels in the electronic structure of a semiconductor. They play a crucial role in determining the electrical properties of the material.

What is the valence band?

The valence band is the highest energy level in the electronic structure of a semiconductor that is fully occupied by electrons. These electrons are tightly bound to the atoms and are not free to move around the material.

What is the conduction band?

The conduction band is the energy level just above the valence band in which electrons are free to move and conduct electricity. This band is only partially filled with electrons, and they can easily move from atom to atom within the material.

What is the energy difference between the valence and conduction bands?

The energy difference between the valence and conduction bands is known as the band gap. This energy gap determines the electrical conductivity of the material. A larger band gap means the material is an insulator, while a smaller band gap indicates a semiconductor.

Can electrons move between the valence and conduction bands?

Yes, electrons can move between the valence and conduction bands when energy is supplied to the material. This can be achieved through various methods, such as applying an electric field or heating the material.

How do valence and conduction bands affect the electrical properties of a semiconductor?

The energy levels of the valence and conduction bands determine the conductivity and resistivity of a semiconductor. When electrons move from the valence band to the conduction band, the material becomes more conductive. This process is known as bandgap engineering and is crucial for creating efficient electronic devices using semiconductors.

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