Q. Basic working of Semiconductors?

Semiconductors are crystalline solid materials whose resistivities have values between those of conductors and insulators. Conductivity ranges fromabout 10^-6 to about 10⁵ S/m. Silicon is by far the most important semiconductor material used today. The conductivity of pure silicon is about  4.35 × 10^-4 S/m. Good electrical characteristics and feasible fabrication technology have been requisites for the prevalence of silicon technology. Compound semiconductors, such as gallium arsenide, are being developed for microwave and photonic applications, while germanium is used for a few special purposes.

When unbound negatively charged electrons move through a crystal, as shown in Figure (a), electrical conduction in semiconductors can take placewith a direction of current opposite to the direction of movement of the electrons.When a bound electron that should be present in the valence bond is missing, the vacancy that arises is known as a hole. Holes are positively charged particles with a charge equal in magnitude to that of the electron.Mobile positively charged holes can also give rise to a current, as shown in Figure (b), with the direction of current in the same direction as the movement of holes. Both holes and unbound electrons are known as charge carriers, or simply carriers.