Abstract
Uncoalesced a-plane GaN epitaxial lateral overgrowth (ELO) structures have been synthesized along two mask stripe orientations on a-plane GaN template by MOCVD. The morphology of two ELO GaN structures is performed by Scanning electronic microscopy. The anisotropy of crystalline quality and stress are investigated by micro-Raman spectroscopy. According to the Raman mapping spectra, the variations on the intensity, peak shift and the full width at half maximum (FWHM) of GaN E2 (high) peak indicate that the crystalline quality improvement occurs in the window region of the GaN stripes along [0001], which is caused by the dislocations bending towards the sidewalls. Conversely, the wing regions have better quality with less stress as the dislocations propagated upwards when the GaN stripes are along []. Spatial cathodoluminescence mapping results further support the explanation for the different dislocation growth mechanisms in the ELO processes with two different mask stripe orientations.
Highlights
Resolved micro-Raman scattering results for mapping the spatial variations in crystalline quality and stress in the ELO a-plane gallium nitride (GaN) structures grown along different mask stripe orientations
To investigate the morphology of the uncoalesced ELO GaN stripes along different orientations, both the samples have been measured by Scanning electron microscopy (SEM)
The cross-section SEM images prove that the vertical growth rate in sample B is faster that of sample A while the lateral overgrowth rate of sample B is slower under this growth condition
Summary
To investigate the morphology of the uncoalesced ELO GaN stripes along different orientations, both the samples have been measured by SEM. The variations in crystalline quality and stress distribution in different regions of sample B can be explained that when GaN grown along [0001] mask stripe direction, many TDs bend during the vertical growth. This phenomenon is explained by the dislocation following a path of minimum elastic energy per unit of growth length of materials[37]. The other region of the GaN stripe is darker which confirms that the intensity of TDs is much higher It indicates that many dislocations in the window region bend to the wing region in sample B. The spatial distributions of dislocations obtained from the CL characterization could further support the dislocation growth mechanisms during the ELO processes in the two samples we propose according to the Raman mapping results
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