A process for forming a single crystal layer of one material type such as III-V semiconductor) onto a substrate of a different material type such as silicon. A substrate of a first material type is provided. At least one discrete region of catalyst material is deposited onto the substrate, the discrete region defining a seed area of the substrate. A second material type such as III-V semiconductor is grown as a single crystal nanowire onto the substrate between the substrate and catalyst material, the nanowire of second material type extending upward from the substrate with lateral dimensions not substantially exceeding the seed area. After growth of the nanowire, growth conditions are changed so as to epitaxially grow the second material type laterally from the single crystal nanowire in a direction parallel to the substrate surface.
