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