There are a number of commonly used methods to determine the bandgap of semiconductor materials.

1. The most common and technically simple is to determine the bandgap from the spectral dependence of the absorption coefficient "alfa" of studied semiconductor materials. Additionally, it is possible to show if the material is a direct or indirect bandgap semiconductor.

2. The second most common method is based on the photoluminescence spectra. The position of their maxima usually directly corresponds to the bandgap energy since it is originated from the bimolecular (band to band) radiative recombination of an electron from the bottom of the conduction band with a hole at the top of the valance band.

3. The most advanced approach to determine the bandgap is to utilize the XPS (x-ray photoelectron spectroscopy) to determine the top of the valance band and IPES (inverse photoelectron spectroscopy) to determine the bottom of the conduction band. However, these techniques are very sophisticated and require expensive highly specialized equipment.

4. An alternative way to determine the bandgap can be applied if there is available a solar cell or a photodiode instead of pure semiconductor material. The extrapolation of the linear temperature dependence of the open-circuit voltage towards 0 K should give a good estimation of the bandgap of the photoactive semiconductor material.

Eventually, it is up to you which approach to chose. All of them can work well as far as you do a careful job of correct measuring and analyzing experimental data.

There are a number of commonly used methods to determine the bandgap of semiconductor materials.

1. The most common and technically simple is to determine the bandgap from the spectral dependence of the absorption coefficient "alfa" of studied semiconductor materials. Additionally, it is possible to show if the material is a direct or indirect bandgap semiconductor.

2. The second most common method is based on the photoluminescence spectra. The position of their maxima usually directly corresponds to the bandgap energy since it is originated from the bimolecular (band to band) radiative recombination of an electron from the bottom of the conduction band with a hole at the top of the valance band.

3. The most advanced approach to determine the bandgap is to utilize the XPS (x-ray photoelectron spectroscopy) to determine the top of the valance band and IPES (inverse photoelectron spectroscopy) to determine the bottom of the conduction band. However, these techniques are very sophisticated and require expensive highly specialized equipment.

4. An alternative way to determine the bandgap can be applied if there is available a solar cell or a photodiode instead of pure semiconductor material. The extrapolation of the linear temperature dependence of the open-circuit voltage towards 0 K should give a good estimation of the bandgap of the photoactive semiconductor material.

Eventually, it is up to you which approach to chose. All of them can work well as far as you do a careful job of correct measuring and analyzing experimental data.

For calculating the band gap UV-Vis diffuse reflectance is the best one.

The optical energy band gap can be calculated by using Tauc relationship

αhν=A(hν-E)^n

For more details you please see the following links:

Article How To Correctly Determine the Band Gap Energy of Modified S...

Article Trap States Passivation and Photoactivation in Wide Band Gap...

You can also use PL but it mostly gives the information related to the recombination rate for photo generated electrons and holes.

for calculating the band gap you can use the Tauc relationship

Many thanks for you Viktor

1) Spectroscopic Ellipsometry

2) Spectroscopic reflectometry

3) Photoreflectance spectroscopy

Patent Bandgap Measurements of Patterned Film Stacks Using Spectros...

Article Strain dependence of the direct energy bandgap in thin silic...

Article Photoreflectance study of GaAsSb/InP heterostructures

Article Photoreflectance spectroscopy of self-organized InAs/InP(0 0...

In addition of Viktor Brus reply and answering to Ouarab Nouredine question:

1) Photoluminescence might give directly the band gap but needs emission/excitation spectra, since the exciton emission can be weak and not always giving the exact band gap value ( see also Bandna Bharti comment on PL). If you read the second reference given by Bandna Bharti , you will see some weird things.

2) Diffuse Reflectance can be a cheap solution :) but only 'as far as you do a careful job of correct measuring and analyzing experimental data' as Viktor wrote. You should be aware of instrumental 'errors' most of them visible when you perform the measurements on standard samples.

see:

https://www.shimadzu.com/an/molecular_spectro/uv/accessory/solidsample/solid.html

http://www.triticeaecap.org/wp-content/uploads/2011/12/Barium_Sulfate.pdf

and the first reference given by Bandna Bharti

3) For materials with sharp direct transition the derivative method can be much better and correct than linear fitting way

see:

Article Exploring the effect of aliovalent substitution of Pb2+ by E...

Article Influence of doping the inorganic cation with Eu or Sb on th...

Article A Novel Approach for the Evaluation of Band Gap Energy in Se...

Article Revisiting the optical bandgap of semiconductors and the pro...

4) Last but not least the Fujiwara and co. papers ( https://www.researchgate.net/profile/Hiroyuki_Fujiwara3/research ) are always highly-educative works (some examples):

Article Maximum Efficiencies and Performance-Limiting Factors of Ino...

Article Tail state formation in solar cell materials: First principl...

Article Optical Characteristics and Operational Principles of Hybrid...

Article Determination and interpretation of the optical constants fo...

Dear Ouarab Nouredine, Tauc (plot) is not an experimental technique to get the Eg, it is a model among many others used to process data obtained from the experimental techniqued. These later are classified as optical and electrical techniques such as those mentionned by Dr. Houssam Chouaib. In the attached file, there is a table which presents other mathematical models. My Regards

This is not a direct answer to the original question but it might be useful.

One method which I use to obtain Eopt from experimental data is the Inverse logarithmic derivative method. See the paper: ''Inverse logarithmic derivative method for determining the energy gap and the type of electron transitions as an alternative to the Tauc method'' in Optical Materials 88 (2019) 667–673

This method is based on the model equation :

d (E) /d ln (alpha E) = (E- Eg)/m

alpha is the absorption coefficient, E the photon energy , m and Eg are the parameters of the linear model which is derived from the model equation

alpha E = A (E- Eg)^m

This method needs the numerical derivative of ln (alpha E) with respect to photon energy E

Dear Ouarab Nouredine ;

I suggest you use photo-reflection spectroscopy, it is a simple and practical technique and at the same time it provides a lot of valuable information.

With my best regards

Hi;

For more details please see the attached documents.

With my best regards

I guess Viktor Brus covered the topic more clearly

Maybe can be calculated by DRS-UV spectroscopy.

As Prof. Viktor Brus has been explained. Where he mentioned most of the methods

In addition, the bandgap can be calculated from the electrical properties

The natural logarithmic of dc conductivity as a function ‎with 1/ T is linearly The activation energy (H) for conduction can be calculated by using the following Arrenhius' formula

ln (σdc )= A –H /KBT

where σdc is the measured dc conductivity (S/m) and A is a constant. T is the temperature in kelvin, and KB is the Boltzman constant

In the middle last century, the activation energy was originally reported as half the bandgap energy for intrinsic conduction.

sorry for the answer - most answers above are pretty good - but what system are you working on? thin films, single crystals, nanoparticles? the "best" answer probably depends on that...

The best method is measured by the photo luminescence where one excites the material by wide band photo flux and measure the spectrum of the emitted light from it. Such spectrum will have peak at the wavelength corresponding to that of the bandgap.

The other equally good method is measuring the absorption coefficient as a function of lambda and then produce Tauc plot from it one can get the gandbap

and its type whether it direct or indirect. This plot can be obtained using spectrometer.

If you do not have spectrometer you can build it using the method developed in the paper: Article LED Based Spectrophotometer can compete with conventional one

Best wishes

In addition to the methods described by Victor, I will add only a method based on a linear approximation of the energy loss spectrum of photoelectron in the XPS method.

The absorption co-efficient curves and Touc plot are sufficient I believe. The film’s optical bandgap (Eg) has been estimated using the Tauc relation

α*h*v=A(hv-Eg)^n

where α is the absorption coefficient, A is a constant, hν is the photon energy, Eg is the material’s optical bandgap. The ‘n’ is realized based on transition type

UV-Visible experimental technique and then you can obtain bandgap by Tauc-Plot

This is usually done by means of optical methods. Nevertheless, it will depend on the form of your material. Is it a thin film, powder, bulk, does it have a rough surface?, it will also depend on the range of the bandgap, if it is wide bandgap material PL might be a bit difficult. CL could be an option there unless it also exhibits excitonic bands.

If it is a powder or piece of material with a rough surface you can use diffuse reflectance and perform the corresponding "Tauc"-plot. (actually, Tauc is the name for the fundamental absorption model of amorphous materials)

If it is bulk material with both fairly flat surfaces, you can use specular Transmittance and reflectance from a standard UV-VIS spectrometer to determine the refractive index and absorption coefficient without the need for a dispersion model.

If it is a thin film or bulk, you can combine, transmittance, reflectance and/or ellipsometry to get the thickness, refractive index and absorption coefficient without the need of a dispersion model, here some examples (doi:10.1063/1.4982894 and doi:10.1364/AO.58.009585).

Subsequently, you will need a proper fundamental absorption model. If the material exhibits a large Urbach tail, it will most likely bias the bandgap determination when using traditional Tauc-like models (here a couple of models you could use doi:10.1088/1361-6463/aaf963).

The bandgap parameter Eg is fundamentally defined from the density of states diagram of a material whereas the experimental band gap such as the optical gap Eopt is a parameter needing a physical interpretation it is not necessarily the bandgap parameter Eg of the material .One hopes to find a definite relation between them to restore the value of Eg . For example Urbach's tail obscures the meaning of the Tauc gap as respectfully mentioned by Guerra above and a physical model is needed as he recommended. The variation of the transition matrix element with photon energy especially in the slower power absorption region i.e. the Tauc region also needs to be better appreciated .