Materials with a small band gap, such as silicon, whose conductivity rises with temperature or doping.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
A semiconductor is a material with a small band gap, typically below about 3 eV, so that some electrons are thermally excited into the conduction band at room temperature. Each excited electron leaves a positively charged hole in the valence band, and both electrons and holes carry current. Unlike metals, the conductivity of a semiconductor increases with temperature because more carriers are generated. Pure semiconductors are called intrinsic, and their conductivity can be changed greatly by controlled doping. Silicon and germanium are the most important examples and form the basis of modern electronics.
Key ideas: Memorize the key facts: intrinsic carriers come in pairs, electron and hole, with number density rising exponentially with temperature. Silicon has a gap of 1.12 eV and germanium 0.67 eV. Group 14 elements are intrinsic, while GaAs and similar compounds from groups 13 and 15 are used for LEDs and lasers. Gap sets emitted light colour in LEDs.
Common mistakes and connections: Students say semiconductors do not conduct, when they conduct moderately, and wrongly believe that heating improves conductivity as in metals. Holes are not physical particles but missing electrons that act as positive carriers. Links to band theory, doping, p-n junctions, solar cells and transistors.
Band gaps range from 0.67 eV in germanium to 5.5 eV in diamond. Below about 3 eV a material is a semiconductor; far above, an insulator. The interactive lesson shows this as a live animation or chart.
Silicon, with a band gap of about 1.1 eV, conducts far better at higher temperatures than at room temperature.
Materials with a small band gap, such as silicon, whose conductivity rises with temperature or doping.
Semiconductors is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Properties of Covalent Compounds, Properties of Metals, Band Theory.
The next topics in Bonding & Molecular Structure are Doping and VSEPR Theory.
Yes. The interactive lesson includes a self-check question on Semiconductors, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Semiconductors is topic 33 of 104 in Bonding & Molecular Structure.