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Material World
Compound · GaAs

Gallium arsenide

The semiconductor that does what silicon cannot — emit light, and switch fast enough for a radio front end.

Semiconductor

Silicon has an indirect band gap, which means an electron falling across it must exchange momentum with the crystal and overwhelmingly releases heat rather than light. Gallium arsenide's gap is direct, and the same transition emits a photon. That single difference is why every semiconductor laser and most light-emitting diodes are built from compound semiconductors rather than from silicon.

Electrons also move through it several times faster than through silicon, which makes it the material of choice for the high-frequency amplifiers in radio equipment — including the power amplifier in essentially every mobile phone.

Economic significance

Gallium arsenide has been the perpetual challenger to silicon and has never seriously threatened it, for reasons that have little to do with performance. Silicon has a cheap, abundant, perfectly behaved native oxide; wafers are larger and far cheaper; and half a century of investment sits behind its processing. The industry saying that gallium arsenide is the material of the future and always will be has been current for forty years.

Where it wins, it wins completely. Semiconductor lasers, high-efficiency multi-junction solar cells for spacecraft, and radio-frequency front ends are all its and are not contested.

The gallium is a by-product of aluminium refining, recovered from Bayer process liquor, and the arsenic is exactly what it sounds like — which makes the fabrication a genuinely hazardous business and the finished device entirely inert.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

  • Gallium — element · recovered from Bayer process liquor, which is the only place gallium comes from in quantity Wikidata
  • Arsenic — element · exactly what it sounds like, which makes fabrication hazardous and the finished device entirely inert Wikidata

is used as

  • Photovoltaics — application · in multi-junction cells for spacecraft, where efficiency per unit area is worth almost any price

is used in

  • Semiconductor manufacturing — industry · the compound semiconductor industry, which is a separate business from silicon with its own fabs and its own economics
  • Electronics manufacture — industry · radio-frequency and optoelectronic devices, where silicon's indirect band gap and lower carrier mobility are the limits

is an alternative to

  • Silicon — element · the perpetual challenger that has never seriously threatened it — silicon has a cheap native oxide, larger wafers and fifty years of investment, and gallium arsenide has the properties silicon lacks entirely
  • Gallium nitride — compound · in radio frequency, where GaN has taken most of the high-power market — GaAs keeps the low-noise and low-power end, which is a different requirement rather than a lost argument

is produced by

  • Czochralski process — process · grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates

is associated with

  • The semiconductor era — event · where silicon's indirect band gap is the limit — radio frequency and optoelectronics

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Gallium arsenide back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is sourced from (reduced with carbon in an electric arc furnace) → Quartz
  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (reduced with carbon to metallic tin) → Cassiterite
  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (reduced with coke in a blast furnace) → Hematite
  • Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (the phosphate rock charged to the electric furnace, with coke to reduce it and silica to take up the calcium) → Apatite

These are the most distinct paths back. Gallium arsenide can be traced through others besides.

Downstream — what it becomes