Abstract
Two yellow luminescence bands related to different defects have been revealed in undoped GaN grown by hydride vapor phase epitaxy (HVPE). One of them, labeled YL1, has the zero-phonon line (ZPL) at 2.57 eV and the band maximum at 2.20 eV at low temperature. This luminescence band is the ubiquitous yellow band observed in GaN grown by metalorganic chemical vapor deposition, either undoped (but containing carbon with high concentration) or doped with Si. Another yellow band, labeled YL3, has the ZPL at 2.36 eV and the band maximum at 2.09 eV. Previously, the ZPL and fine structure of this band were erroneously attributed to the red luminescence band. Both the YL1 and YL3 bands show phonon-related fine structure at the high-energy side, which is caused by strong electron-phonon coupling involving the LO and pseudo-local phonon modes. The shapes of the bands are described with a one-dimensional configuration coordinate model, and the Huang-Rhys factors are found. Possible origins of the defect-related luminescence bands are discussed.
Highlights
Two yellow luminescence bands related to different defects have been revealed in undoped GaN grown by hydride vapor phase epitaxy (HVPE)
We have identified the YL1 band with its zero-phonon line (ZPL) and fine structure in other samples, including C-doped and Fe-doped semi-insulating GaN layers on sapphire grown by metalorganic chemical vapor deposition (MOCVD), Fe-doped, freestanding GaN grown by HVPE, and undoped GaN grown by molecular beam epitaxy (MBE)
The YL1 band has a maximum at 2.20 eV and the ZPL at 2.57 eV at low temperatures, and the RL1 band has a maximum at 1.80 eV
Summary
Two yellow luminescence bands related to different defects have been revealed in undoped GaN grown by hydride vapor phase epitaxy (HVPE). That the activation energies obtained from photoluminescence (PL) quenching may vary for different samples and are not necessarily equal to the defect ionization energy[15] Both positive and negative correlations between the intensity of the YL band and the concentrations of the C and VGa defects were reported. Xu et al.[16] observed a much stronger YL band in high-resistivity GaN with high concentration of C and very low concentration of VGa as compared to conductive n-type GaN samples. In the latter, the intensity of the YL band correlated with the concentration of VGa in three samples.
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