conductors, semiconductors & Insulators

• Solids can be categorised into conductors, semiconductors, or insulators based on their ability to conduct electricity
• In metals, the highest occupied band is the conduction band, which is not completely full, allowing electrons to move and conduct
• Insulators have a full valence band and a large gap between the valence and conduction bands, preventing electrical conduction at room temperature
• In semiconductors like silicon and germanium, the gap between the valence and conduction bands is smaller than in insulators, allowing some electrons to move into the conduction band at room temperature
• An increase in temperature increases the conductivity of a semiconductor
• Doping semiconductors with certain elements can produce n-type and p-type semiconductors
• 1. type semiconductors introduce 5-valent atoms like phosphorus or arsenic, leading to surplus electrons as main current carriers
• 1. type semiconductors introduce 3-valent atoms like boron or indium, leading to positive holes as main current carriers
• Crystals of silicon or germanium can have p-n junctions, which have specific electrical properties important in the electronics industry
• LEDs are forward bias p-n junctions that emit photons of light when electrons move from the conduction band to the valence band
• Solar cells use p-n junctions to absorb photons, allowing electrons to move from the valence band to the conduction band, creating a potential difference known as the photovoltaic effect