The GaN/substrate bi layer is cooled from a growth temperature at which the bulk layer is grown to {HEAD ~ an ambient temperature}, wherein {TAIL ~ GaN material} of the bi layer cracks laterally and separates from the substrate to form a substantially crack free free standing GaN article 
wherein
The GaN / substrate bi layer is cooled from a growth temperature at which the bulk layer is grown to { HEAD ~ an ambient temperature } , wherein { TAIL ~ GaN material } of the bi layer cracks laterally and separates from the substrate to form a substantially crack free free standing GaN article
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