Semiconductor Fundamentals · Topic 4 of 13
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Bandgap
The energy gap between the valence and conduction bands — the number that defines a semiconductor.
What you’ll learn
- What the bandgap is and its units
- Typical values for common materials
- How the bandgap affects devices
Why it matters
Bandgap sets how easily carriers are created, the wavelengths a material emits or absorbs, and its temperature behaviour.
Explanation
The bandgap (Eg) is the minimum energy an electron needs to jump from the valence band to the conduction band, measured in electron-volts (eV). Silicon's is about 1.1 eV, germanium's about 0.66 eV, and gallium arsenide's about 1.4 eV. Insulators have gaps of several eV.
A smaller gap means carriers are generated more easily (higher intrinsic conductivity, more leakage); a larger gap suits high-temperature and high-power devices and sets the colour of LEDs and the response of photodetectors.
Visual explanation
Key terminology
- Bandgap (Eg)
- Energy needed to promote an electron to the conduction band.
- Electron-volt (eV)
- A convenient energy unit at the atomic scale.
- Direct/indirect gap
- Whether an electron can cross the gap without a momentum change — key for light emission.
Formula
A material tends to emit/absorb light with photon energy near its bandgap.
Example
Common mistakes
Watch out for:
- Confusing a large bandgap with 'better' — the right gap depends on the application.
- Ignoring that silicon's indirect gap makes it a poor light emitter.
Real-world application
Wide-bandgap SiC and GaN power devices switch faster and run hotter than silicon.
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Bandgap
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Intrinsic semiconductor
Semiconductor Fundamentals
A pure, undoped semiconductor where electrons and holes come only from thermal generation.
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