A band gap is the energy range in a solid where no electron states exist. Electrons must acquire at least this much energy to move from the valence band to the conduction band. Its magnitude determines electrical conductivity and optical absorption properties.

Why does wavelength decrease as band gap increases?

Photon energy and wavelength are inversely related (E = hc/λ). A larger band gap requires a higher-energy photon to bridge it, and higher-energy photons have shorter wavelengths.

What is the boundary between semiconductor and insulator?

The boundary is conventional, not sharp. Most references treat E_g ≤ 4 eV as semiconductor territory (silicon: 1.12 eV, GaN: 3.4 eV). Diamond at 5.5 eV is a classic insulator. This tool uses 4 eV as the threshold.

Can I enter a band gap of zero?

Yes. Zero band gap corresponds to a metal or semimetal (e.g., graphene). The photon energy would also be zero, so wavelength and frequency are undefined — the tool will note this.

What common semiconductors can I test?

Try silicon (1.12 eV), germanium (0.67 eV), GaAs (1.42 eV), GaN (3.4 eV), or ZnO (3.37 eV).

Band Gap Calculator

Name: Band Gap Calculator
Availability: InStock
Author: Nham Vu

Convert semiconductor band gap energy between eV and joules, find the corresponding photon wavelength and frequency, and classify the material type.

Band Gap Input

Band gap energy (eV)

Band gap energy (J)

Common semiconductors

Enter a band gap energy value to see results

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Summary

Convert semiconductor band gap energy between eV and joules, find the corresponding photon wavelength and frequency, and classify the material type.

How it works

Enter a band gap energy value in eV or joules.
The tool converts between eV and joules using 1 eV = 1.602176634 × 10⁻¹⁹ J.
Photon frequency is computed as f = E / h, where h = 6.62607015 × 10⁻³⁴ J·s.
Photon wavelength is computed as λ = hc / E, where c = 2.99792458 × 10⁸ m/s.
Material class is determined: metals (E_g ≈ 0), semiconductors (0 < E_g ≤ 4 eV), insulators (E_g > 4 eV).

Use cases

Determine the minimum photon energy needed to excite electrons across a semiconductor band gap.
Find the cut-off wavelength for photodetectors or solar cells made from a given material.
Convert textbook band gap values between eV and SI joules for equations.
Classify an unknown material based on its measured band gap.
Cross-check experimental optical absorption edges against theoretical band gap values.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu