A method for forming a III-V construction over a group IV substrate comprises providing an assembly comprising the group IV substrate and a dielectric thereon. The dielectric layer comprises a trench exposing the group IV substrate. The method further comprises initiating growth of a first III-V structure in the trench, continuing growth out of the trench on top of the bottom part, growing epitaxially a sacrificial second III-V structure on the top part of the first III-V structure, and growing epitaxially a third III-V structure on the sacrificial second III-V structure. The third III-V structure comprises a top III-V layer. The method further comprises physically disconnecting a first part of the top layer from a second part thereof, and contacting the sacrificial second III-V structure with the liquid etching medium.