It has already been suggested, but why is POET acquiring wafers? Are they actually going to be producing chips or are they vetting suppliers for feasability/confidentiality reasons? The wafers have to be going to a semi-manufacturer of some repute, and again, as already mentioned, if they are buying wafers, they sure as hell are not doing it for fun, they are going to be selling finished products to someone.
Also, why are we suddenly so interested in GaA wafers, and who says the wafers will be GaA's? A couple of months ago when the COO was announced we were going to be using silicon wafers of some sort with VCSEL's attached.
This definition suggests that epitaxy is used for both silicon and GaA chip construction.
https://en.wikipedia.org/wiki/Epitaxy
Epitaxy is used in silicon-based manufacturing processes for bipolar junction transistors (BJTs) and modern complementary metal–oxide–semiconductors (CMOS), but it is particularly important for compound semiconductors such as gallium arsenide. Manufacturing issues include control of the amount and uniformity of the deposition's resistivity and thickness, the cleanliness and purity of the surface and the chamber atmosphere, the prevention of the typically much more highly doped substrate wafer's diffusion of dopant to the new layers, imperfections of the growth process, and protecting the surfaces during the manufacture and handling.