UNIT 2 • WHY SILICON?

Silicon by the numbers

≈ 28% of the crust

Silicon is the second most abundant element in Earth's crust after oxygen, at roughly 28 percent by mass. It is found bound to oxygen in sand and quartz, so the raw material is essentially free.

The hard part isn't finding silicon. It's purifying it.

BAND GAPS

How the semiconductors compare

Germanium 0.66 eV · the first transistors, but leaky at room temperature

Silicon 1.12 eV · the balanced workhorse

Gallium arsenide 1.42 eV · fast electrons and good light emission

Silicon carbide about 3.3 eV · high-voltage, high-temperature power

Gallium nitride about 3.4 eV · power, radio, and blue LEDs

A wider band gap tolerates more voltage and heat; a narrower one switches at lower energy but leaks more.

SILICON'S SUPERPOWERS

Why it won

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A native oxide

Heating silicon in oxygen grows SiO₂, a stable, high-quality insulator that bonds cleanly to the crystal

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A wide processing window

It melts at 1,414 °C and tolerates the high temperatures that oxidation and doping need

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Controllable conductivity

Tiny amounts of boron or phosphorus set how well it conducts

The best transistor material is the one you can build a whole ecosystem around.

WHERE OTHERS WIN

What silicon can't do well

Emitting light Silicon's indirect band gap makes a poor light source, so LEDs and lasers use III-V compounds

Very fast radio Gallium arsenide and related compounds move electrons faster, for some RF uses

High-voltage power Silicon carbide and gallium nitride handle more voltage and heat

Silicon wins on cost and ecosystem, so it's used unless something else is essential.

GERMANIUM'S FALL

Why the first material lost

Ge oxide: water-soluble

The first transistor in 1947 used germanium. But germanium's oxide is unstable and dissolves in water, and its small band gap makes it leak heavily at room temperature. Silicon's robust oxide made reliable integrated circuits possible.

The oxide, not just the crystal, made silicon the winner.

UNIT 2 STUDY COMPLETE

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Ready for the Fab Challenge?

You can explain why silicon beat the alternatives, and where other materials still win.