Semiconductor

A semiconductor is a material whose conductivity can be controlled — by doping it, by illuminating it, or by applying a field to it — and that controllability is the whole of its usefulness. Its own conductivity, which is poor, is beside the point.

Silicon dominates and is not the best of these at anything electrical. It won because it forms a stable, adherent, insulating native oxide, which is what makes the planar process possible. The compound semiconductors here exist where silicon's band gap or carrier mobility is the limit — light emission, high frequency, high power.

• Compound

  Cadmium telluride

  with a band gap of about 1.5 eV, close to the theoretical optimum for converting sunlight

• Element

  Gallium

  A metal that melts in the hand, and the basis of every blue and white LED.

• Compound

  Gallium arsenide

  direct band gap, which is what lets it emit light — the property silicon fundamentally lacks

• Compound

  Gallium nitride

  with a band gap of 3.4 electron volts against silicon's 1.1 — which is what puts blue light and high-voltage switching within reach and puts both out of silicon's

• Element

  Germanium

  The semiconductor the transistor was invented in, then displaced by silicon.

• Material

  Polysilicon

  and the purity is the product: at these levels an unwanted atom in a billion measurably shortens the carrier lifetime

• Element

  Silicon

  The second most abundant element in the Earth's crust, and the substrate of essentially all modern electronics.

• Compound

  Silicon carbide

  in high-temperature and high-voltage power electronics

Each of these uses is established and cited on its own. Whether something counts as an ore, for instance, depends on grade, price and era — and those qualifications are shown alongside it.