http://www.ask.com/wiki/Gallium_arsenide?o=2801&qsrc=999&ad=doubleDown&an=apn&ap=ask.com
Read the GaAs advantages and Si advantages to get a better picture.
From my memory, I think Oogee pointed out that GaAs is a recycleable compound.
I too, agree that JOEL H 's comments have been good for the rankin file here as it provides fuel for us to do further research into this " potentially disruptive technology".
Thanks Joel and GLTA!