Semiconductor Basics

3Types of Semiconductors

OBJECTIVES OF THIS CHAPTER

In the previous chapter we saw that the energy levels in gaseous atoms become energy bands when they form a solid and atoms and electrons interact with each other. The band concept allowed us to understand the difference between conductors, insulators, and semiconductors depending on how full or empty the allowed energy bands are and how large or small the gap between conduction and valence band is.

In this chapter we deal with semiconductors and how I can change their electrical properties by purposely adding impurities. One of the great advantages of the semiconductors is that I can dope, that is, add a control number of impurities, and change drastically the electrical properties of the semiconductors. We will look at the crystallographic formation and how electron hold bonds with neighboring atoms.

3.1 Semiconductor Materials

There are many semiconductor materials, each having its own advantages and disadvantages. Figure 1.17 I showed a portion of the Mendeleev's periodic table that includes all the elements that we use as semiconductors. The single element semiconductors are those in group IV. Group IV elements are those materials that have four valence electrons, that is, four electrons in the outermost orbit or on the valence band. These are also the main semiconductor materials we use, silicon and germanium. There are also compound semiconductors where the number of valence electrons averages four (e.g. groups ...