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

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Discussion Overview

The discussion centers around the differences between valence and conduction bands in semiconductors, particularly in the context of LEDs. Participants explore the definitions and roles of these bands, as well as their relation to p-type and n-type materials.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant seeks a simple definition of valence and conduction bands and their relation to p-type and n-type materials in LEDs.
  • Another participant explains that the valence band is the topmost band filled with electrons, while the conduction band is above it, where electrons can move freely when an electric field is applied.
  • It is noted that the valence band of p-type semiconductors is rich in holes, while the conduction band of n-type semiconductors is rich in electrons.
  • A later reply suggests that if the doping level is closer to the conduction band, the material is n-type, and if closer to the valence band, it is p-type, with corresponding dominant charge carriers being electrons and holes, respectively.
  • Some participants express confusion about the topic, indicating that they are self-learning and seeking clarification.

Areas of Agreement / Disagreement

Participants express varying levels of understanding, with some clarifying concepts while others remain confused. There is no consensus on the simplest explanation, as different participants provide different levels of detail and clarity.

Contextual Notes

Some participants indicate that their understanding is based on learning materials, which may not have fully clarified the concepts. There is also mention of a resource (Hyperphysics) that could provide additional information.

nst.john
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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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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.
 
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.
 
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!
 
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.
 

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