Semiconductors are materials whose resistivity is affected by the addition of impurities. These materials have unique electrical properties that make them useful in various electronic devices.

Semiconductors:
Semiconductors are materials that have electrical conductivity between conductors (such as metals) and insulators (such as glass or rubber). The conductivity of semiconductors can be controlled by adding impurities, a process called doping. Doping introduces atoms of different elements into the semiconductor crystal lattice, which alters its electrical properties.

Doping:
Doping can be of two types: n-type and p-type. In n-type doping, impurities with extra electrons, such as phosphorus or arsenic, are added to the crystal lattice. These extra electrons become mobile and contribute to the conductivity of the material. In p-type doping, impurities with fewer electrons, such as boron or gallium, are added. These impurities create "holes" in the crystal lattice, which can be thought of as vacancies where an electron could be. These holes also contribute to the material's conductivity.

Effect on Resistivity:
The addition of impurities significantly affects the resistivity of semiconductors. In pure semiconductors, also known as intrinsic semiconductors, the resistivity is relatively high. However, when impurities are added through doping, the resistivity decreases, allowing better electrical conduction.

Applications:
Semiconductors are the foundation of modern electronics. They are used in various electronic devices, including transistors, diodes, solar cells, and integrated circuits (ICs). The ability to control their conductivity through doping makes them versatile for different applications.

Transistors, for example, are made using doped semiconductors and serve as amplifiers or switches in electronic circuits. Solar cells use semiconductors to convert sunlight into electrical energy. Integrated circuits, or microchips, are made using layers of doped semiconductors and are the building blocks of computers, smartphones, and other electronic devices.

Conclusion:
Semiconductors are materials whose resistivity is affected by the addition of impurities through a process called doping. This unique property allows for the control of electrical conductivity and enables the development of various electronic devices.