Introduction to Materials: Conductors, Insulators, and Semiconductors

Introduction to Materials

• Solids can be classified into three main categories: conductors, insulators, and semiconductors based on their electrical conductivity.
• Conductors allow electric current to flow through them with minimal resistance, examples include copper, gold, and aluminum.
• Insulators resist the flow of electric current, examples include wood, glass, and rubber.
• Semiconductors have intermediate conductivity, and their electrical conductivity can be controlled, examples include silicon and germanium.

Atomic Structure and Electrical Conductivity

• The electrical conductivity of a material is determined by the arrangement of its electrons in the atomic structure.
• In conductors, the outermost energy level is not fully occupied, allowing electrons to move freely and conduct electricity.
• In insulators, the outermost energy level is fully occupied, preventing electrons from moving freely and conducting electricity.
• In semiconductors, the outermost energy level is partially occupied, allowing some electrons to move freely and conduct electricity under certain conditions.

Energy Bands and Electrical Conductivity

• The energy levels of electrons in a material can be represented by energy bands, which are ranges of energy levels.
• The valence band is the lowest energy band, where electrons are bound to the atom, and the conduction band is the highest energy band, where electrons are free to move.
• In conductors, the valence band and conduction band overlap, allowing electrons to move freely between the two bands.
• In insulators, the valence band and conduction band are separated by a large energy gap, preventing electrons from moving between the two bands.
• In semiconductors, the valence band and conduction band are separated by a small energy gap, allowing some electrons to move between the two bands under certain conditions.