The invention relates to a process for producing a composite body (36) having at least one functional layer or for the further use for producing an electronic or optoelectronic component (40, 42, 44). The composite body (36) is in the form of a layer structure and comprises at least one substrate (34), which is in the form of a plate and has at least one planar substrate surface, and at least one substantially polycrystalline or at least one substantially single-crystal layer (38), which comprises at least one compound semiconductor, a ceramic material or a metallic hard material.The process is characterized by the following steps: heating at least part of the planar substrate surface to a temperature of at least 100° C. and at most 550° C.; cleaning the substrate surface by supplying hydrogen from a first material source (20) and a plasma produced specifically therefor; terminating the substrate surface by applying carbon, nitrogen or oxygen from the first material source (20) or a second material source (22) and a plasma produced specifically therefor; and growing the at least one layer (38) by supplying material components of the compound semiconductor, of the ceramic material or of the metallic hard material from the first material source (20) and the second material source (22) to the at least one planar substrate surface. The invention also relates to the use of the composite body (36) produced according to one of the disclosed embodiments of the process or a combination thereof for producing an electronic or optoelectronic component.