Epitaxial wafers are different from chips. Epitaxial film refers to a semiconductor film grown on a single crystal with a crystal structure matching, with Gan as an example, a complex Gan film (including-, quantum well,-, etc.) is grown on a sapphire ($literal), which is called epitaxy. The chip refers to the extension of the processing, its main purpose is to add electrodes on the extension, in order to be packaged and applied. The main material of the chip is the monocrystalline silicon is not correct, still is GAN material. It can be said that Epitaxy is the raw material of the chip, the chip is on the basis of the extension of the electrode (some chips also do passivation film, mirrors and so on.
