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Temperature stress experiments up to 800/spl deg/C have been applied to AlGaN/GaN FET's grown by MOVPE on sapphire and their individual technological building blocks. It was found that the temperature limit is given by the irreversible degradation of the intrinsic active heterostructure material itself during operation above 600/spl deg/C. The irreversible degradation was observed for both unconnected and electrically operated devices during temperature stress.
Daumiller et al. (Wed,) studied this question.