Photoluminescence study of undoped, doped GaN grown on (00.1), (11.0), (01.2)Αl 2 O 3 (100), (111)Si, and (00.1)6H-SiC substrates have been conducted.Strong bandedge emissions from all undoped samples and dopant--related emissions from doped samples were observed.Deep-level yellow emissioii centered around 2.2 eV was not observed from undoped GaN grown on 6H-SiC substrate, undoped GaN with optimum Ga source flow and doped GaN.The experiment data strongly suggest that Ga vacancies are the origin this deep-level emission.
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Zhang et al. (1995) studied this question.