Overview

In textbooks on solid-state physics, a semiconductor is usually defined rather loosely as a material with electrical resistivity lying in the range of 10 ^?2 10 ⁹ ? cm. ^[1] Alternatively, it can be defined as a material whose energy gap (to be defined more precisely in Chap. 2) for electronic excitations lies between zero and about 4 electron volts (eV). Materials with zero bandgap are metals or semimetals, while those with an energy gap larger than 3 eV are more frequently known as insulators. There are exceptions to these definitions. For example, terms such as semiconducting diamond (whose energy gap is about 6 eV) and semi-insulating GaAs (with a 1.5 eV energy gap) are frequently used. GaN, which is receiving a lot of attention as optoelectronic material in the blue region, has a gap of 3.5 eV.

The best-known semiconductor is undoubtedly silicon (Si). However, there are many semiconductors besides silicon. In fact, many minerals found in nature, such as zinc-blende (ZnS) cuprite (Cu ₂O) and galena (PbS), to name just a few, are semiconductors. Including the semiconductors synthesized in laboratories, the family of semiconductors forms one of the most versatile class of materials known to man.

Semiconductors occur in many different chemical compositions with a large variety of crystal structures. They can be elemental semiconductors, such as Si, carbon in the form of C ₆₀ or nanotubes and selenium (Se) or binary compounds such as gallium arsenide (GaAs).