electronic and phonon relaxation time versus doping

[eliephys78]

Dear all,

I am trying to compute transport properties for some materials (Seebeck, electronic conductivity, thermal lattice conductivity, etc). The code I am using allows to compute these properties for different electron/hole concentrations. However I have been setting the electronic lifetime ($\tau_{el}) (that I obtain from EPW) to be the same for all concentrations. I have realized that we can redefine the Fermi energy using EPW. My question is : To what extent keeping the electronic lifetime constant is correct? Can EPW recalculate $\tau_{el}$ for different electronic concentrations (after redefining the Fermi energy)?

Regards
Elie Moujaes
Federal university of Rondonia
Brazil

[sponce]

Dear eliephys78,

The scattering rate does depend on band fractional occupation. You can approximate by keeping the lifetime constant and this should be ok for very low doping/intrinsic doping.

Note that large doping will have many effects, including changing the bandstructure (polaron etc).

The best in my opinion is to test it for your own system in the condition you are interested in and determine whether is is important or not.

[eliephys78]

Thank you for your answer,

I just got two more small questions:

1- What I am doing in my calculations is that I am calculating the average of $\tau_{n,k}$ over all bands and and all points for say the 11 Wannier functions I considered and using it in subsequent transport calculations. Is this correct or do I have to separate relaxation times for holes and electrons? if so,

2-How to calculate the hole and electron relaxation times separately? Do I consider the average of \tau over all conduction bands for electron relaxation time and all over all valence bands for the hole relaxation time or do i have to ONLY consider the maximum valence band for holes and minimum conduction band for electrons?

Thanks again