A method of fabricating at least one single-crystal alloy semiconductor structure, comprising: forming at least one seed (7; 7a-d) on a substrate for growth of at least one single-crystal alloy semiconductor structure, the at least one seed (7; 7a-d) containing an alloying material; providing at least one structural form on the substrate the at least one structural form being formed of a host material having a higher melting point than the alloying material, and comprising a main body which extends from the at least one seed (7; 7a-d) and a plurality of elements which are connected to the main body in spaced relation along the main body; heating the at least one structural form such that the material of the at least one structural form has a liquid state, the liquid state comprising the host material and the alloying material, and cooling the at least one structural form, such that the material of the at least one structural form nucleates at the at least one seed (7; 7a-d) and crystallizes as a single crystal to provide the at least one single-crystal alloy semiconductor structure, with a growth front of the single crystal propagating along the main body of the respective structural form in a direction away from the respective seed (7; 7a-d); wherein the plurality of elements of each structural form provide reservoirs of the alloying material in liquid state, such that as single crystal growth proceeds along the main body, successive ones of the plurality of elements act to maintain, in liquid state, an available supply of the alloying material to the growth front of the single crystal in the main body of the respective structural form. forming at least one seed (7; 7a-d) on a substrate for growth of at least one single-crystal alloy semiconductor structure, the at least one seed (7; 7a-d) containing an alloying material; providing at least one structural form on the substrate the at least one structural form being formed of a host material having a higher melting point than the alloying material, and comprising a main body which extends from the at least one seed (7; 7a-d) and a plurality of elements which are connected to the main body in spaced relation along the main body; heating the at least one structural form such that the material of the at least one structural form has a liquid state, the liquid state comprising the host material and the alloying material, and cooling the at least one structural form, such that the material of the at least one structural form nucleates at the at least one seed (7; 7a-d) and crystallizes as a single crystal to provide the at least one single-crystal alloy semiconductor structure, with a growth front of the single crystal propagating along the main body of the respective structural form in a direction away from the respective seed (7; 7a-d); wherein the plurality of elements of each structural form provide reservoirs of the alloying material in liquid state, such that as single crystal growth proceeds along the main body, successive ones of the plurality of elements act to maintain, in liquid state, an available supply of the alloying material to the growth front of the single crystal in the main body of the respective structural form.