Lu100, larger GaAs wafers don't pose larger problems. At least that was my impression when I heard Stephane Gagnon talking about that topic.

According to Stephane, the reason that no 8 inch GaAs wafers are available today, is not that they are hard to produce, but that customers don't ask for them (enough). This is about to change with POET going into mass production, and wafer makers are able and willing to deliver 8 inch wafers. Stephane quoted this example to show that POET also triggers innovations at their suppliers.

Oh, and I suppose this might also be true for even larger wafers.