A couple of quick questions on screening / lattice deformation

[rwooduk]

If a material is doped (introducing positive dopants to the lattice) there will be a build up of negative cahrge around them, screening. I have a couple of questions that seem obvious but I'm still a little unsure:

1) how would more screening effect resistivity? I would assume that a build up of negative charge would hinder conduction but the impression I'm getting from the notes is that it increases conductivity??

2) (possibly unrelated to screening) if say the dopant has smaller atoms and introduced defects into the lattice please could someone tell me how that would effect the phonons? if that makes sense? how would a lattice deformation effect resistivity / conductivity.

I have all the formulas for calculations but I'm trying to visualise these effects a little more. Any help would really be welcome.

 

[BigJDubs]

1) The build up of negative charge around a dopant will usually increase the conductivity of the material by creating additional pathways for electrons to travel. This is because the extra negative charge reduces the repulsive forces between electrons, making it easier for them to move through the material. 2) If the dopant has smaller atoms, this will introduce defects into the lattice which will affect the phonons. Phonons are quanta of vibrational energy that travel through the lattice and are responsible for the thermal properties of the material. A lattice deformation due to the dopant will change the phonon properties, resulting in changes to the thermal conductivity of the material. This in turn can affect the resistivity of the material, depending on the nature of the defect and how it interacts with the electrons.