A method for manufacturing a growth substrate adapted for producing by epitaxy a matrix of diodes based on InGaN, comprising the following steps: - providing a crystalline stack based on GaN, comprising: a doped lower layer; and an upper layer made from In x2 Ga 1-x2 N with x2>0, resting on and in contact with the doped lower layer; where: - the doped lower layer has a predefined proportion of indium x1≥0 such that it is non-absorbent to an illuminating light radiation having a predefined central wavelength, and the upper layer has a predefined proportion of indium x2>0 such that it is absorbent of illuminating light radiation; - the doped lower layer has a predefined doping level such that it is porosifiable at an electrical voltage of predefined value V ECE, and the upper layer has a predefined doping level such that it is non-porosifiable at the predefined electrical voltage V ECE; - producing mesas M (i), with i ranging from 0 to 2, by localised etching of the upper layer to form upper portions of mesas and of at least a part of the lower layer doped to form lower portions of mesas; then - depositing an encapsulation layer made of an electrically insulating material, covering at least one mesa denoted M, such that said mesa M is not porosified during an electrochemical porosification of mesas denoted M and M; then - electrochemically porosifying the lower and upper portions of at least one mesa M by: photo-assisted porosification of the upper portion of the mesa M by emission of the illuminating light radiation; and non-photo-assisted porosification of the lower portion of the mesa M by application of the electrical voltage of value V ECE; - electrochemically porosifying only one of the lower and upper portions of at least one mesa M by: photo-assisted porosification of the upper portion of the mesa M during that of the upper portion of the mesa M; or non-photo-assisted porosification of the lower portion of the mesa M during that of the lower portion of the mesa M; - removing, at least in part, the encapsulation layer, so as to expose an upper surface of the mesa M. - providing a crystalline stack based on GaN, comprising: a doped lower layer; and an upper layer made from In x2 Ga 1-x2 N with x2>0, resting on and in contact with the doped lower layer; where: - the doped lower layer has a predefined proportion of indium x1≥0 such that it is non-absorbent to an illuminating light radiation having a predefined central wavelength, and the upper layer has a predefined proportion of indium x2>0 such that it is absorbent of illuminating light radiation; - the doped lower layer has a predefined doping level such that it is porosifiable at an electrical voltage of predefined value V ECE, and the upper layer has a predefined doping level such that it is non-porosifiable at the predefined electrical voltage V ECE; - the doped lower layer has a predefined proportion of indium x1≥0 such that it is non-absorbent to an illuminating light radiation having a predefined central wavelength, and the upper layer has a predefined proportion of indium x2>0 such that it is absorbent of illuminating light radiation; - the doped lower layer has a predefined doping level such that it is porosifiable at an electrical voltage of predefined value V ECE, and the upper layer has a predefined doping level such that it is non-porosifiable at the predefined electrical voltage V ECE; - producing mesas M (i), with i ranging from 0 to 2, by localised etching of the upper layer to form upper portions of mesas and of at least a part of the lower layer doped to form lower portions of mesas; then - depositing an encapsulation layer made of an electrically insulating material, covering at least one mesa denoted M, such that said mesa M is not porosified during an electrochemical porosification of mesas denoted M and M; then - electrochemically porosifying the lower and upper portions of at least one mesa M by: photo-assisted porosification of the upper portion of the mesa M by emission of the illuminating light radiation; and non-photo-assisted porosification of the lower portion of the mesa M by application of the electrical voltage of value V ECE; - electrochemically porosifying only one of the lower and upper portions of at least one mesa M by: photo-assisted porosification of the upper portion of the mesa M during that of the upper portion of the mesa M; or non-photo-assisted porosification of the lower portion of the mesa M during that of the lower portion of the mesa M; - removing, at least in part, the encapsulation layer, so as to expose an upper surface of the mesa M.