There is described a method of manufacturing a substrate for an optoelectronic device. The method has the steps of: supporting a first layer of a first crystalline material on a second layer of a second crystalline material different from said first crystalline material thereby exposing crystalline defects at a surface of said first layer; etching said first layer using first etching conditions, at least some of said crystalline defects expanding into pores running from said surface of the first layer towards said second layer; and heating said first and second layers up to a first temperature for a first period of time within a given environment, said heating transforming said pores into nanovoids attracting at least some of said crystalline defects away from said surface. In some embodiments, the method has a step of reheating the layers or a step of forming a pore containing region within the first layer.