The method successively comprises production, on a substrate, of a stack of layers comprising at least one first layer made from germanium and silicon compound initially having a germanium concentration comprised between 10% and 50%. The first layer is arranged between second layers having germanium concentrations comprised between 0% and 10%. Then a first zone corresponding to the germanium-based element and having at least a first lateral dimension comprised between 10 nm and 500 nm is delineated by etching in said stack. Then at least lateral thermal oxidization of the first zone is performed so that a silica layer forms on the surface of the first zone and that, in the first layer, a central zone of condensed germanium forms, constituting the germanium-based element.