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