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 (10, 20) via said contact faces (17a, 25a). 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 (10, 20) via said contact faces (17a, 25a).