Band Gap Energy Calculator

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Calculator

Method

Pick how you want to estimate Eg.

Wavelength λ (nm)

Eg(eV) ≈ 1240 / λ(nm).

Frequency f (THz)

Eg = h·f / q.

Energy (J)

Eg(eV) = E(J) / q.

Material preset

Select a preset or enter custom constants.

Eg(0 K) (eV)

Band gap at 0 Kelvin.

Temperature T (K)

Room temperature is about 300 K.

α (eV/K)

Temperature coefficient.

β (K)

Material constant in Kelvin.

Note (optional)

Saved with exports and history.

Varshni model: Eg(T) = Eg0 − α·T² / (T + β)

Saved calculations (latest first)

Stored in your session (up to 50 rows).

Time	Method	Inputs	Eg (eV)	λ (nm)	f (THz)	Note
No saved calculations yet. Submit the form to store results.

Example data table

Material	Absorption edge λ (nm)	Estimated Eg (eV)	Notes
Silicon (Si)	1107	1.120	Near room temperature, indirect gap.
Germanium (Ge)	1870	0.663	Indirect gap, strong temperature dependence.
GaAs	817	1.518	Direct gap, efficient optoelectronics.
GaN	365	3.397	Wide band gap, UV/blue devices.

These rows are illustrative. Real values vary by doping, strain, and temperature.

Formulas used

Eg(eV) ≈ 1240 / λ(nm) from photon energy and wavelength.
Eg(eV) = (h·f)/q where f is frequency in Hz.
Eg(eV) = E(J)/q for Joules to electron‑volts conversion.
Eg(T) = Eg0 − α·T²/(T + β) (Varshni temperature model).
Equivalents: λ = h·c/E and f = E/h.

How to use this calculator

Select a method that matches your measurement.
Enter wavelength, frequency, energy, or temperature constants.
Press Calculate to show results above the form.
Repeat calculations; the session table keeps recent rows.
Use Download CSV or Download PDF anytime.

FAQs

1) What is band gap energy?

It is the energy difference between the valence band and conduction band. Photons below the gap usually cannot create free carriers in an ideal semiconductor.

2) Why does wavelength estimate Eg?

At the absorption edge, photon energy roughly matches the electronic transition threshold. Using E = hc/λ gives Eg in electron‑volts after unit conversion.

3) When should I use the Varshni model?

Use it when you know the material constants and temperature. It helps estimate how Eg shifts with temperature for many common semiconductors.

4) Are preset constants always correct?

They are typical reference values. Thin films, strain, alloying, and heavy doping can change Eg and temperature behavior, so measured data should be preferred.

5) What does “equivalent frequency” mean?

It is the photon frequency that has the same energy as the computed band gap. It is useful when you work with spectroscopy or THz/IR sources.

6) Why are my results different from datasheets?

Datasheets may specify direct vs indirect gaps, different temperatures, or alloy compositions. Measurement methods also differ, so ensure you compare the same conditions.

7) How do exports work?

Each calculation is stored in your browser session on the server. The CSV and PDF downloads include the saved rows, so export after you run all needed cases.