Some customers worry about that when they transfer LED onto other substrates using laser liftoff, these patterns of LED wafer on patterned sapphire substrate. PSS will scatter the laser. In fact, some of our customers also use 4” epi wafers on PSS for LLO, it is no problem. That is because:
1.”laser lift-off” actually is according to “NL layer” as below image. If the NL layer is GaN layer, when it is heating to constant high temperature, the GaN is decomposed into Ga and nitrogen, and nitrogen is released out, naturally the sapphire is seperated from epitaxial layer.
So the main point is if the NL layer is GaN layer or not (some manufacturers use NL layer by AlN material, if so, it can not be laser lift off.)
And we confirm our NL layer is GaN material.
2. we will polish the back side of PSS substrate, which is the same function as LED wafer on flat sapphire.