A GaN-based electronic and/or optoelectronic device (10) formed on a free-standing GaN substrate (12), wherein a thick GaN spacer layer (14) is provided between the device and the substrate, thereby separating the active region of the electronic and/or optoelectronic device from high impurity content at the substrate-epitaxial interface and reducing the detrimental impact of such interfacial impurity on the performance of the electronic and/or optoelectronic device. The GaN spacer (14) layer has a thickness of at least about 0.5 microns, and preferably from about 0.5 micron to about 2 microns.
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