Читать книгу Semiconductor Basics - George Domingo - Страница 32

In this chapter, we have seen how as we shrink the interatomic distance between atoms, due to the Pauli exclusion principle the gaseous energy levels spread and become bands. We call the lowest energy band that has electrons the valance band and the one above it, empty of electrons, the conduction band. Depending on how many electrons are in the valence band and how far the valence and conduction bands are separated, we have conductors, insulators, or semiconductors.

At absolute zero, the valence band of a semiconductor is completely full, and the conductions band is empty. The separation between the bands is small. At room temperature, there is quite a bit of thermal energy, and a very small number of electrons have sufficient energy to move to the conduction band – and they are free to move. In the valence band, the missing electrons leave a hole that acts as if it were a positive charge.

The key concepts in this chapter that you need to understand to proceed to the next chapter are as follows:

 The concepts of a valence band and a conduction band.

 The concept that a small energy gap is required for an electron to move to the conduction band.

 The concept of the hole – an atom missing an electron, which, under an applied voltage, accepts an electron from a neighboring atom, thus moving the hole toward the negative terminal as if it were a positive charge.

If you are comfortable with these concepts, you are ready to go to the next chapter.