Nov 11, 2019

Advantages and remaining issues of state-of-the-art m-plane freestanding GaN substrates grown by halide vapor phase epitaxy for m-plane InGaN epitaxial growth

Advantages and remaining issues of state-of-the-art m-plane freestanding GaN (FS-GaN) substrates grown by halide vapor phase epitaxy (HVPE) for m-plane InxGa1 − xN epitaxial film growth by metalorganic vapor phase epitaxy are described. Because of the low threading dislocation and basal-plane stacking fault densities, improved quantum efficiency and short radiative lifetime are achieved for the near-band-edge emission of 200–250 nm thick m-plane pseudomorphic InxGa1 − xN (x ≤ 0.14) epilayers. Values of full-width at half-maximum for the x-ray ω-rocking curves remain unchanged as the substrate values being 80 and 60 arcsec for the (10$\bar{1}$0) diffraction with 〈0001〉 and $\langle 11\bar{2}0 \rangle$ azimuths, respectively, and 80 arcsec for the (10$\bar{1}$2) diffraction. As the surface flatness is greatly improved, the In-incorporation efficiency (ηIninc) is lower than the cases for conventional c-plane growth and m-plane growths on defective GaN bases. The former originates from nonidentical surface kinetics, and the latter is due to the reduction in the area of inclined and tilted planes. Sub-micrometer-wide zonary patterns parallel to the c-axis and 2 μm long axis figure-of-eight patterns parallel to the a-axis are clearly visualized in the monochromatic cathodoluminescence (CL) intensity images. Because the spatio-time-resolved CL measurement reveals very little spatial variation of low-temperature radiative lifetime, the slight peak energy variation is interpreted to originate from nonidentical ηIninc for the growing surfaces exhibiting various miscut angles. The figure-of-eight patterns are ascribed to originate from the anisotropic, severe m-plane tilt mosaic along the a-axis of the GaN substrate, and the zonary patterns may originate from the m-plane tilt mosaic along the c-axis. Further reduction in the tilt and twist mosaics is necessary for HVPE of FS-GaN substrates, in order to grow homogeneous InGaN epilayers.


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