You may find also a graph: energy gap narrowing at high doping levels

http://www.ioffe.ru/SVA/NSM/Semicond/GaAs/bandstr.html#Doping

A handwaving argument: the incorporation of doping ions may lead to compression of the host lattice

As I know GaAs has a spontaneous polarization. This polarization should be affected by doping and cause a red shift. ( Like Stark effect which cause red shift in quantum wells).

Of course, compressive strain introduced into GaAs can cause a red-shift and I agree that changes of an built-in electric field can be a reason for red shifting of the edge in GaAs quantum wells (but I'm not sure that zinc blende GaAs has spontaneous polarization). Indeed, I'm interested in narrowing phenomena caused by many body interactions. Any clues?

Lukasz I totally agree the spontaneous polarization could be seen in wurtzite structure but your doping as u said causes a built-in electric field. However, I wonder what u mean with narrowing, is it like GaAs nanowire?

The Burstein-Moss effect causes the blue shift, not the red one. The exchange interaction in electron or hole plasma leads the band gap narrowing, but the magnitude of the narrowing is very small in this case (less than ten meV approximately). As Thomas Mayer mentioned, it may be also lattice-related effect.

The red shift is due to band gap narrowing because of high doping or high carrier concentration effects. Please see the paper in the link:https://www.researchgate.net/profile/Abdelhalim_Zekry/publications/?page=2&sorting=newest&linkType=fulltextFile

red shift was discussed on the basis of direct energy transfer between different states.

please view the paper for more information.

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