The invention concerns a device (10) for forming in single-crystal state a compound body with incongruent evaporation, capable of being in monocrystalline or polycrystalline form, comprising at least one first chamber (20) containing a substrate (42) whereat is formed a polycrystalline source of said body and a monocrystalline germ (46) of said body; a second chamber (14), said substrate being arranged between the two chambers; means for input (36) of gaseous precursors of said body into the second chamber capable of bringing about deposition of said body in polycrystalline form on the substrate; and heating means (26) for maintaining the substrate at a temperature higher than the temperature of the germ so as to bring about sublimation of the polycrystalline source and the deposition on the germ of said body in monocrystalline form.