Epitaxial lateral overgrowth of GaN structures: spatially resolved characterization by cathodoluminescence microscopy and micro-Raman spectroscopy

The epitaxial lateral overgrowth of GaN structures is comprehensively characterized by scanning cathodoluminescence microscopy and micro-Raman spectroscopy. The samples under study consist of a 3-μm thick GaN buffer layer grown by MOVPE on (0001) sapphire and subsequently structured using a SiO2 mask. The resulting stripe pattern is overgrown with HVPE GaN. Mask orientations along 〈1100〉 and 〈1120〉 are compared. CL microscopy directly visualizes the significant differences between the overgrown areas on top of the SiO2-mask and the coherently grown regions between the SiO2-stripes. The overgrown GaN shows a blue shift and a strong broadening of the luminescence. In contrast, the local luminescence from the areas of coherent (0001)-growth is dominated by narrow excitonic emission. The CL results are correlated with micro-Raman spectroscopy yielding information on the local strain and free carrier concentration.