Hi all
i am trying to see the influence of elemental doping on the DOS plots and want to compare with the pristine structure.
But when the doping is done, i found the VB side energies are crossing the Fermi energy (Fermi level shifted to Zero) levels and going into negative side. I am using VASP and the usual steps like (1) optimize, (2)SCF, and then (3)DOS calculations.
please see the figure after the doping is done.
the pristine model is a Perovskite and this attached figure is after doping Aluminium
Can anyone suggest what could went wrong?
Regards.
As per the definition of extrinsic semiconductor there is formation of two type of semiconductor based on dopant (1) n-type, when the dopant is electron rich in which case the fermi is shifted towards conduction band, while (2) p-type, when electron deficient dopant shift the fermi energy towards the valence band. So aluminium doping leads to formation of exrinsic semiconductor.
Brajesh Rajesh Bhagat Thanks a lot for very quick answer. Let me get clarify more on your response.
1. Attaching the pristine Perovskite DOS also for comparison.
2. the difference in both plots, show around 2 eV shift of VB towards CB. Is in't it too much of a shift? i have replaced only one atom of Lead with one atom of Aluminium in a super-cell. My worry here is, if there is any calculation error, in first place?
3. Electron affinity of Aluminium (Al) is more Than Lead (Pb) --> 42.5 kJ/mol (Al) and 31.5 kJ/mol (Pb). Does this play a role here, as per your response above?
4. All said and done, but the plotting scheme/software supposed to 'shift' Fermi energy to ZERO. That means, as per your definition, there still be more negative energy bands than Fermi value, that were introduced by Aluminium?
Regards
2. Change of fermi when you replace 3s2, 3p1 element (Al) in place of 6s2, 6p2 element (Pb) is obvious and no error could be sensed.
3. Since electron affinity is difference of vacuum energy and conduction band minima there could be a relationship in this case
4. Yes but the would depend on the concentration of Al since i don't know what is the size of supercell and concentration of Al ?
Brajesh Rajesh Bhagat Thank you again for details.
2. So, its because of a 'net short fall' of electrons compared with original case. Right?
4. The super cell contain total 72 atoms. Both in original and doped. One Pb from original is replaced with one Aluminium in doped. Original Pb atoms = 16. In the doped Pb = 15 + ONE Al atom.
please offer your opinion.
Regards
2. True, the net short fall of electrons or we would prefer to say formation of p-type semiconductor which decrease the Pb states too along with the fermi shift.
4. 6% doping is enough to confirm the huge change apart from the orbital difference.
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