You have met the term on datasheets and want a plain answer. What is band gap in semiconductors? It is the energy, in electron-volts, between a material’s valence and conduction bands, and it shapes chips, LEDs and power parts.
This guide sits within the site’s reads on semiconductor basics, so it stays focused on the band gap itself.
| Material or term | Band gap value |
|---|---|
| Silicon (Si), indirect | 1.12 eV |
| Germanium (Ge), indirect | 0.661 eV |
| Gallium arsenide (GaAs), direct | 1.42 eV |
| Silicon carbide (SiC), indirect | 3.26 eV |
| Gallium nitride (GaN), direct | 3.4 eV |
| Wide band gap threshold | wider than about 2 eV |
These figures come from a PCIM article on direct and indirect band gap semiconductors and a semiconductor materials reference page last updated in July 2019. References differ slightly and figures can change, so check the source before you rely on them.
Band gap in plain terms
The band gap is the energy separation between a semiconductor’s valence band and its conduction band. It is quoted in electron-volts (eV), the unit used for every value on this page. One materials reference describes a wide band gap semiconductor as one with an energy band gap wider than about 2 eV.
The number matters because it points to the job a material suits. Direct band gap materials serve photonics and solar cells, while standard electronics is built on indirect band gap silicon. If the material itself is new to you, read what is a semiconductor first.
Why does direct or indirect decide whether a material glows?
The size of the gap is only half the story. In a direct band gap material such as gallium arsenide, the valence and conduction bands are aligned with respect to momentum, so electron-hole recombination readily releases light. In an indirect material such as silicon, the bands are misaligned and recombination releases heat instead of light.
That is why direct band gap semiconductors are used in LEDs, laser diodes and solar cells. A reference page says the same thing in short form: indirect gap materials are inefficient at emitting light, and direct gap materials are good light emitters. Silicon and germanium, the most common semiconductors, are both indirect, according to the PCIM article.
Light absorption follows the same split. Direct gap materials show a high absorption coefficient near the band edge, and indirect ones show a low one. Once photon energy exceeds the band gap, absorption becomes large in direct materials but rises only gradually in indirect ones.
Band gap values for common materials
Here are the values from the PCIM article and the materials reference, grouped by what each material is known for:
- Silicon: 1.12 eV, indirect, the base of standard electronics.
- Germanium: 0.661 eV, indirect and narrow.
- Gallium arsenide: 1.42 eV, direct, used in infrared LEDs, laser diodes and solar cells.
- Gallium phosphide: 2.26 eV, indirect, still used for green and red LEDs with nitrogen-doped engineering.
- Silicon carbide: 3.26 eV, indirect, used in power electronics such as EV traction and solar inverters.
- Gallium nitride: 3.4 eV, direct and wide.
Two references do not always agree to the last digit. The PCIM article lists germanium at 0.7 eV, while the materials reference lists 0.661 eV, and gallium arsenide appears as 1.42 eV in one and 1.424 eV in the other. Treat these as close approximations and quote your source.
Mixing materials can also move the number. The materials reference lists aluminium gallium arsenide, an alloy, at 1.42 – 2.16 eV and direct.
The wider list of materials shows how far the numbers spread. The materials reference puts indium antimonide at 0.17 eV and indium arsenide at 0.354 eV, both narrow. At the other end it lists aluminium nitride and boron nitride at 6.2 eV, both wide.
Here is how a few of those extra materials are used, with figures from the materials reference and the PCIM article:
- Indium phosphide: 1.344 eV, direct and narrow, used in high-power and high-frequency electronics and in laser diodes.
- Indium arsenide: 0.354 eV, narrow, used in infrared detectors and diode lasers.
- Indium antimonide: 0.17 eV, narrow, used in infrared detectors and thermal imaging cameras.
- Gallium oxide: 4.8 eV, indirect, used for deep UV detection and solar-blind UV photodetectors.
- Diamond: 5.47 eV in the PCIM article and 5.46 eV in the reference, used for heat sinks and spreaders in power electronics.
- Aluminium nitride: 6.2 eV, wide, used for electronic substrates with high thermal conductivity.
A wide gap therefore does not always mean a power transistor. Diamond and aluminium nitride appear mainly as heat-handling parts and substrates, while the narrow-gap indium compounds lean toward infrared sensing. The gap value is one clue, and the direct or indirect type, the application and the source all matter too.
Germanium shows how a material’s role can shift. The May 2026 PCIM article calls it a historic semiconductor used in Schottky diodes and radar pulse detection, and lists its uses alongside silicon (SiGe BiCMOS) in fiber optics, infrared components, imaging cameras and RF components.
Narrow versus wide band gap in practice
Reference pages draw the line at about 2 eV. A narrow band gap semiconductor sits below it and suits tunnel devices and infrared technology. A wide one sits above it and, per the same reference, suits microwave devices.
Power electronics is where wide gaps get the most attention. The poor performance of silicon in high-power electronics pushed engineers to look for alternatives, and the PCIM article from May 2026 says wide band gap semiconductors are driven by silicon carbide and gallium nitride. You can read the full article for the details.
There is a twist here. SiC is indirect and GaN is direct, yet the same article says that behaviour does not affect the choice between them. That choice depends on breakdown field, power density, electron mobility and thermal conductivity.
For everyday logic and memory, silicon’s indirect gap is no obstacle. To see how that silicon becomes working circuits, read what is an integrated circuit.
How engineers find a band gap value
Engineers use optical absorption spectroscopy to measure band gap energy. They analyse the result with a Tauc plot of absorption coefficient against photon energy. In plain terms, they watch how strongly a material absorbs light as photon energy rises.
This is one reason you should read a datasheet’s conditions before comparing values. Check which source a figure comes from and what it was measured on.
Frequently asked questions
What is band gap in semiconductors, in simple words?
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It is the energy gap between the valence band and the conduction band of a material, quoted in electron-volts. Different materials have different gaps, which is why silicon, gallium arsenide and silicon carbide suit different jobs.
Is a bigger band gap better?
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Neither is better in general. The materials reference links narrow gaps to tunnel devices and infrared technology and wide gaps to microwave devices, so the right choice depends on the application.
Why is silicon not used for most LEDs?
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Silicon has an indirect band gap, so recombination releases heat rather than light. The PCIM article notes that most photonic devices are made from other compounds rather than silicon.
Does direct or indirect decide between SiC and GaN?
Show answer
No. The PCIM article says that behaviour does not affect the choice, which depends on breakdown field, power density, electron mobility and thermal conductivity.
