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Crystalline III-V channels can be grown epitaxially on silicon substrates, with buffer layers to grade the strain due to crystal lattice mismatch. With silicon wafers heading to 450mm diameter the economics would argue against native III-V substrates.

One advantage of native III-V substrates is they are semi-insulating (very high resistivity) so there is no need for transistor isolation wells. However, insulated substrates could be obtained on silicon by means of wafer bonding with an intermediate dielectric layer.