Dear,
i doped Si on the BeO and run band calculation. I have attached the band structure of BeO and Si doped BeO. In doped band structure, the some energy states exceed the fermi level. The fermi level is 13.69 Ev eV. and the beginning of the Si doped band structure is 12.49 eV below the fermi level. So, the energy states of Si is found 1.2 eV. Right ?
I have a few inputs regarding this.
1. Generally, while plotting band-structures, most people keep (E-Ef) in the y axis, which means the zero-level indicates the Fermi level. If your assignment of the Fermi level is correct, then I guess you have not followed the above-mentioned convention.
2. Doping will add additional bands, as well as modify the existing bands. This is because the space-group or symmetry is compromised. So, you may calculate projected bands for a comprehensive understanding.
3. If your Fermi level crosses a few bands, then the material is considered as metallic. Therefore, the concept of band-gap does not apply here.
4. You have not mentioned the k-mesh that you have taken for calculation. For accurate data, a robust k-mesh is needed.
5. You have not mentioned the doping percentage of silicon. Normally oxidation state of Be is 2 and silicon is 4. Therefore, if you dope too much Si into Be site, a lot of additional electrons will come up making it a n-type material, and even metallic.
6. Please create a supercell and dope Si up to a rational amount, say 4%. This will probably not make it metallic.
Dear Souvik Bhattacharjee thanks for your reply. the si concentration is 3. 125 % in all atoms. I created supercell 2x2x2 (32 atoms) one Be atom is replacing one Si atom. Also fermi level is illustrated red dashed line at 13.69 eV.
In a semiconductor the position of the Fermi energy has some degree of freedom. Some codes put it at the maximum of the valence band, others in the middle of the band gap. In a metal, on the other hand, the Fermi energy is determined by the occupation. In your case, you go from a semiconductor to a metal with your doping level.
Clearly, your evaluation of the position of the Si level is arbitrary. This is due to the fact that the two structure might be referred to two different energies (for example the binding energies of the two structures are different)— remember only energy differences have a physical meaning. So it would be better if you can analyse (for example with a PDOS analysis) where your Si doping atoms contribute to the band structure. This procedure might give you a better understanding of the effect of doping in your system.
On the other hand, do you know if the doped BeO is a metal? If not, your analysis might be wrong and lead by the large number of extra electron you are inserting in the system.
Roberto D'Agosta thanks to for your detail reply. BeO exhibit metallic behavior by dopind other element. I didnt find the Si doped BeO in DFT or experimentally
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