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Impacts of vacancy complexes on the room-temperature photoluminescence lifetime of state-of-the-art GaN substrates, epitaxial layers, and Mg-implanted layers
For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission (𝜏PLRT) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, 𝜏PLRT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm-3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively. While, major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3-4, inammonothermal GaN. The values of 𝜏PLRT in n-GaN samples are compared with those of p-GaN, in which 𝜏PLRT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers while by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealings, respectively.
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- 08/05/2024
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JAP135(2024)185701_GaNMGRCWalukiewiczTribute.pdf | 3.84 MB | MDR Open |
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