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I've read papers in DFT studies on band gap tuning in semiconductors and the usually studied methods are either through doping or application of external strain. But it is always just one or the other. I've never come across any paper where they investigated how simultaneously varying both the amount of doping and strain affects the electronic structure of materials. Why is this so? Is there some physics-based reason for this or is it just because simultaneously varying both the amount of doping and strain might be computationally expensive?

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  • $\begingroup$ +1 Doping and strain are two largely independent tuning parameters, so I doubt there is a fundamental reason for this. My guess is that it is simply computationally expensive, and in a give project it is typically best to focus on one effect. You could always extend your question and say: why not strain+doping+temperature, or strain+doping+temperature+electric field, and so on. $\endgroup$ – ProfM Sep 19 '20 at 15:48
  • $\begingroup$ +1. Thank you for bringing this from Physics.SE to here! Hopefully you will have better luck finding an answer here :) $\endgroup$ – Nike Dattani Sep 20 '20 at 2:22
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I suspect the reason is due to the model. Often doping is performed in the dilute doping region where you do not relax the cell to optimize the strain induced by the adsorbate. This is because it is assumed the doping is done in a way that the bulk structure imposes its lattice constant on the dopant. The dopant actually does induce strain so they are not independent of each other.

The problem becomes experimentally creating a doped and strained material. Growing a thin film that is doped (one way to induce strain) will probably result in segregation of the dopant. For this reason its probably just not well explored. If an experimentally tunable system is identified where both knobs can be turned independently, doping and strain, this would be well suited to dft studies.

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I've never come across any paper where they investigated how simultaneously varying both the amount of doping and strain affects the electronic structure of materials. Why is this so?

  • Doping and strain are viewed as effective methods to engineer the properties of materials. It is true that doping and strain can be applied at the same time. However, from the viewpoint of simulation, we don't want to do that. Because we hardly deduce that the final results are engineered by what method. For example, if the strain will open the gap, but the doping will close the gap. Then the final result manifests the gap doesn't change. Can we say that strain and the doping don't affect the band-gap of materials? Or can we say that strain will close the gap and the doping will open the gap?

Is there some physics-based reason for this or is it just because simultaneously varying both the amount of doping and strain might be computationally expensive?

  • The computation amount depends on many elements: such as the number of the atom, the sampling of k mesh and the energy cutoff, and so on.
  • If you just want to study strain, then you can choose the primitive cell. The computational amount will keep a minimum.
  • If you want to study doping, then the cell is decided by the concentration with the supercell method.
  • If you want to study doping and strain simultaneously, the cell is also decided by the concentration with the supercell method. Therefore it doesn't change the computational amount compared with the doping simulation.
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