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  Semiconductor Physics, Part 1 
  Jan 21, 2003, 08:30am EST 


By: Dan Mepham

Here’s a brief synopsis of the key information derived in this article:
  • When we bring together many atoms to form a substance, we observe the formation of two energy bands; a Conduction and Valence Band.
  • Electrons can exist in either of these two energy bands, but not in between. Electrons trapped in bonds are in the Valence Band, while electrons broken free of the bonds are in the Conduction Band.
  • The conduction Band is higher energy; electrons in the Conduction Band have more energy than those in the Valence Band.
  • With no outside excitation (i.e., zero light, zero temperature, etc.), all electrons will reside in the Valence band.
  • Those electrons in the Valence Band are not available for electrical conduction.
  • When we apply light or temperature, a small number of electrons gain enough energy to jump into the Conduction Band, and thus can participate in conduction.
  • The conductivity of a silicon material is directly proportional to the number of electrons available in its Conduction Band. Thus, by altering the number of electrons in the Conduction Band, we can dramatically change the electrical characteristics of our Silicon.
We’ve thrown a lot of information at you in this first installment of our series, so take a look back, and re-read anything that doesn’t make sense. A solid foundation is key to understanding the future installments, so be certain that you’re comfortable with the concepts. Don’t be discouraged if it seems complicated; what we’ve covered in just a few pages is material sufficient for an entire University-level course.

By all means, if you have unanswered questions, post them to our discussion forms. Odds are someone else has the same question.

We hope you’ve enjoyed the first look at Semiconductor Physics. Stay tuned for Part 2, where we’ll talk about doping, and p- and n-type materials.

Dan Mepham

Part 2 has been posted, and is available here.

1. Introduction
2. Before the 'How', Ask Yourself 'Why?'
3. Crystal Structure, Forming the Bonds
4. Electron Energy Levels
5. Band Formation, Things Get Complicated
6. Electron Excitation, Making the Leap
7. Summary

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