Process for fabricating an optoelectronic device for emitting infrared light radiation, comprising the following steps: i) producing a first stack comprising: • a light source of exciting light radiation, • a first bonding sublayer made from a metal of interest chosen from gold, titanium and copper, having a first contact face , • between which is placed a first binding layer made from a material that is transparent to the exciting light radiation; ii) producing a second stack comprising: • a GeSn-based active layer suitable for absorbing the exciting light radiation and for emitting in response the infrared light radiation, having an atomic proportion of tin (x Sn ) such that it has a direct electronic-band structure, and being obtained by epitaxial growth at an epitaxy temperature (T epi ), • a second bonding sublayer made from said metal of interest, having a second contact face , • between which is placed a second binding layer made from a material that is transparent to the exciting light radiation; iii) determining an assembly temperature (T c ) comprised between an ambient temperature (T amb ) and said epitaxy temperature (T epi ), to within 10%, such that a direct bonding energy per unit area of said metal of interest is higher than or equal to 0.5 J/m 2 ; iv) joining, by direct bonding, at said assembly temperature (T c ), said stacks via said contact faces . i) producing a first stack comprising: • a light source of exciting light radiation, • a first bonding sublayer made from a metal of interest chosen from gold, titanium and copper, having a first contact face , • between which is placed a first binding layer made from a material that is transparent to the exciting light radiation; • a light source of exciting light radiation, • a first bonding sublayer made from a metal of interest chosen from gold, titanium and copper, having a first contact face , • between which is placed a first binding layer made from a material that is transparent to the exciting light radiation; ii) producing a second stack comprising: • a GeSn-based active layer suitable for absorbing the exciting light radiation and for emitting in response the infrared light radiation, having an atomic proportion of tin (x Sn ) such that it has a direct electronic-band structure, and being obtained by epitaxial growth at an epitaxy temperature (T epi ), • a second bonding sublayer made from said metal of interest, having a second contact face , • between which is placed a second binding layer made from a material that is transparent to the exciting light radiation; • a GeSn-based active layer suitable for absorbing the exciting light radiation and for emitting in response the infrared light radiation, having an atomic proportion of tin (x Sn ) such that it has a direct electronic-band structure, and being obtained by epitaxial growth at an epitaxy temperature (T epi ), • a second bonding sublayer made from said metal of interest, having a second contact face , • between which is placed a second binding layer made from a material that is transparent to the exciting light radiation; iii) determining an assembly temperature (T c ) comprised between an ambient temperature (T amb ) and said epitaxy temperature (T epi ), to within 10%, such that a direct bonding energy per unit area of said metal of interest is higher than or equal to 0.5 J/m 2 ; iv) joining, by direct bonding, at said assembly temperature (T c ), said stacks via said contact faces . <EOS>