Semiconductors conduct electricity due to a small bandgap, allowing electrons to move between the valence and conduction bands under certain conditions.
Semiconductors and Electrical Conduction
Semiconductors are unique materials that have electrical properties between conductors and insulators. Unlike metals, which have a high number of free electrons, semiconductors have a limited number of free charge carriers under normal conditions. However, their conductivity can be greatly increased by altering their composition and external conditions. This article explains how semiconductors conduct electricity.
Band Theory and the Role of Energy Bands
Understanding semiconductor conductivity requires a basic knowledge of energy bands. In solid materials, electrons occupy specific energy levels, known as bands. The two main bands in semiconductors are the valence band, where electrons are bound to atoms, and the conduction band, where electrons are free to move and conduct electricity. The energy gap between these bands is called the bandgap.
In semiconductors, the bandgap is relatively small, allowing some electrons to move from the valence band to the conduction band under certain conditions. This movement of electrons results in electrical conduction.
Intrinsic and Extrinsic Semiconductors
There are two types of semiconductors based on their composition and conductivity: intrinsic and extrinsic.
- Intrinsic Semiconductors: These are pure semiconductor materials, like silicon or germanium, that have no impurities. At absolute zero temperature, they behave like insulators. However, as the temperature increases, some electrons gain enough energy to jump from the valence band to the conduction band, creating electron-hole pairs. The movement of these electrons and holes enables electrical conduction in intrinsic semiconductors.
- Extrinsic Semiconductors: These are semiconductors that have been doped with small amounts of impurities to intentionally modify their electrical properties. Extrinsic semiconductors can be further divided into two types:
- N-Type: These are doped with donor atoms that have more valence electrons than the semiconductor material. The additional electrons can easily move to the conduction band, increasing conductivity.
- P-Type: These are doped with acceptor atoms that have fewer valence electrons than the semiconductor material. The absence of electrons creates holes in the valence band that can move under an electric field, also increasing conductivity.
Role of Semiconductors in Electronic Devices
Semiconductors play a crucial role in modern electronics. Their unique electrical properties allow them to be used in a wide range of devices, such as transistors, diodes, and integrated circuits. By controlling the flow of current through semiconductors, engineers can design electronic components that perform specific functions, enabling the development of advanced technologies in computing, communication, and more.
