Take GaAs as an example. If we assume there are some deep levels inside the GaAs bandgap caused by point defects, like vacancy or antisite, when strain is applied on it, we know the bandgap will change, then how will the defect levels change their energy? Are there any common rules?
Dear Yuxin,
I would say you must discuss all properties which effect on the position of energy levels. Strain effects on the lattice parameter and therefore on the band structure. The bands shift and therefore the effective masses. The dielectric constant changes and the position of the quasi fermi level. You observe isolator metal transitions. Generally, strain generates a new material..
For flat energy levels (hydrogen like level) almost the permittivity and the effective mass change the ionization energy with respect to the band edges. For deep level must be discussed from which values their energy depends.
Regards
R. Mitdank
Dear Rüdiger,
Thanks very much for the answer!
So it is a complicated problem, and needs to be theoretically calculated case by case.
Regards,
Yuxin
Dear Yuxin Song,
I would like to add a suggestion.
If you would like, please calculate the electronic structure of the systems using DFT method (try the well-known and well-built GGA or LDA methods) for such complicated problem. I expect that there would be a strain-dependent trend of defect levels change.
Regards,
S. Muhammady
Dear yuxin song,
The question you asked is very interesting and challenging to answer correctly but I would like to add some comments.
To calculate the energies of deep level you need to know the defect potential which is very difficult to calculate for deep levels as the displacement of atoms can occur and both the impurity and host atoms can be involved in the lattice relaxation. Deep levels craeted by point defects like vacancy also involve lattice relaxation. A vacancy of atom in a covalent bond produces dangling bonds which can be cured by forming pairs of bonds among neighbouring dangling bonds. As a result of this atoms with dangling bonds have to move closer to each other in order to form new bonds and this atomic displacement involves an elastic energy which is compensated for by lowering of the energy of electrons in dangling bonds.
This decrease in energy of electrons can be calculated from the overlap parameters of "tight binding model".
Now external strain (hydrostatic pressure )also involve the atomic displacement which may effect the defect potential of deep levels.
You may also refer the book "Fundamental of Semiconductor: physics and materials properties" by Peter Y.Yu, Manuel Cardona.
Regards
A.S. Sharma
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