Dear all,
In order to calculate the band gap of a given semiconductor material we use the following Tauc formula: (ahv)=A(hv-Eg)^n. We define A as a constant in all the papers. The question is what's it's value ? Should we take it equal to unity ?
Best regards,
Dr. A. CHETOUI
Dear Abdel :
I got interested by your question, however I have just used the relationship as (ahv)=(hv-Eg)^n , never seen it with this A coefficient at the front.
Sorry !, regards !
Dear Franklin,
You can find the Tauc formula with the "A" constant in many papres. May be you just havent come across the good paper. Otherwise, I think that the constant "A" is taken equal to unity. Please find here attached some files which describe the Tauc formula with the constant "A".
Best wishes,
A. CHETOUI
Hi,
the A coefficient depends on the structure of the material. The value of A changes with the disorder ( impurities, dangling bonds...).
regards !
Dear Mr. Chetoui,
As mentioned by Khadjida above the variation of the constant A (so-called also Tau's factor) indicates the changing in material structure. Indeed, its diminution can be in general explained by the increase of structural desorder due to inactif dopants, dangling bonds, vacancies, etc...
Good luck!
Dear Ms. Ketroussi, dear Mr. Khelifati,
Thank you a lot for your help. However, if the constant A depends on the material's structure, we've to attribute to it a value. otherwise, we can't use the Tauc formula with two unkown parameters (A and Eg). If possible, could you give me an example of a cetrain value of A correspondingly to a given structure ?
genially,
A. CHETOUI
Dear Mr.Chetoui
The coefficient A is a characteristic of the structure. It is independent of the wavelength. In the representation of (ahv)=A*(hv-Eg)^n , the value of (A) is obtained by the slope of the straight line. For example, in hydrogenated amorphous silicon (a-Si:H), the value of A is about 531 (cm.eV)^-1/2.
regards!
Hi again,
You're welcome!
Please find in attached file an example of experimental findings obtained on Boron-doped hydrogenated amorphous silicon for different boron concentration. It is well known that boron incorporation into silicon matrix with high density increases the structural disorder. Such disorder was observed in the diminution of optical gap Eg as well as Tauc's factor B0. The value of B0 can be directly correlated with the slop of the valence and conductance band tails.
Kindly, -Nabil
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