Semiconductor Band Gap Calculator: Electronic Pr...

What is a Semiconductor Band Gap?

The band gap is the energy difference between the valence band (filled) and conduction band (empty) of a material. Conductors have no gap (bands overlap). Insulators have large gaps (>4 eV). Semiconductors have moderate gaps (0.1–3.5 eV) that enable electronic switching — the basis of all modern electronics.

💡 Band Gap Calculator

Free calculator for instant results.

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📐 Formula

Eg(T) = Eg(0) − αT² / (T + β)

Varshni equation: Eg(0) = band gap at 0 K, α and β = material constants. For Si: Eg(300K) ≈ 1.12 eV. For GaAs: 1.42 eV. For Ge: 0.66 eV.

📝 Worked Example

Silicon at 300K: Eg(0)=1.169 eV, α=4.9×10⁻⁴, β=655K
Eg(300) = 1.169 − (4.9×10⁻⁴ × 90000)/(300+655)
= 1.169 − 0.046 = 1.12 eV

📝 How to Use

Select SemiconductorChoose Si, Ge, GaAs, GaN, or enter Varshni parameters manually.

Enter TemperatureOperating temperature in Kelvin or Celsius.

Calculate Band GapView Eg in eV at the specified temperature.

Determine Cutoff Wavelengthλ_c = hc/Eg — the maximum wavelength of light the semiconductor absorbs.

❓ FAQ

Why does band gap decrease with temperature?

Thermal expansion increases lattice constant and electron-phonon interactions broaden and lower the bands, reducing Eg slightly with increasing temperature.

What is a direct vs indirect band gap?

In a direct gap (GaAs), photon emission/absorption is efficient — used in LEDs and lasers. In indirect gap (Si, Ge), phonons are needed — less efficient for optoelectronics.