The GaN/substrate bi layer is cooled from 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 {HEAD ~ the substrate} to form {TAIL ~ a substantially crack free free standing GaN article} 
to form
The GaN / substrate bi layer is cooled from 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 { HEAD ~ the substrate } to form { TAIL ~ a substantially crack free free standing GaN article }
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