Method for manufacturing a mixed substrate

A method for manufacturing a mixed substrate which comprises, on a main face of a support substrate, a first region comprising a first single crystal material and a second region, contiguous to the first region and comprising a second material, the method comprising the steps of:

• a) providing a starting substrate which comprises a stack comprising at least one intermediate layer overlaying the main face of the support substrate, the intermediate layer comprising the second material in a single crystal or polycrystalline form;
• b) forming a mask on the stack, said mask comprising an aperture delimiting location of the first region;
• c) etching the stack at the aperture so as to form a cavity delimited by a bottom and walls, the bottom being located on or in the support substrate;
• and
• d) forming the first region by epitaxially growing the first single crystal material in a single crystal form in the cavity,
• wherein the method comprises a step c1), performed before step d), of forming a protective layer, made of an amorphous material, exclusively covering the walls of the cavity and leaving the bottom of said cavity exposed to an external environment.