The determining factor of a preferred orientation of GaN domains grown on m-plane sapphire substrates.

Chinkyo Kim,Cheol-Woon Kim,Young-Kyun Kwon,Seoung-Hun Kang,Dongsoo Jang,Hansub Yoon,Miyeon Jue

doi:10.1038/srep16236

Chinkyo Kim, Cheol-Woon Kim + Show 5 more

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https://doi.org/10.1038/srep16236

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Abstract

Epitaxial lateral overgrowth in tandem with the first-principles calculation was employed to investigate the determining factor of a preferred orientation of GaN on SiO2-patterned m-plane sapphire substrates. We found that the (100)-orientation is favored over the (10)-orientation in the region with a small filling factor of SiO2, while the latter orientation becomes preferred in the region with a large filling factor. This result suggests that the effective concentration determines the preferred orientation of GaN: the (100)- and (10)-orientations preferred at their low and high concentrations, respectively. Our computational study revealed that at a low coverage of Ga and N atoms, the local atomic arrangement resembles that on the (10) surface, although the (100) surface is more stable at their full coverage. Such a (10)-like atomic configuration crosses over to the local structure resembling that on the (100) surface as the coverage increases. Based on results, we determined that high effective concentration of Ga and N sources expedites the growth of the (10)-orientation while keeping from transition to the (100)-orientation. At low effective concentration, on the other hand, there is a sufficient time for the added Ga and N sources to rearrange the initial (10)-like orientation to form the (100)-orientation.

Highlights

Technological importance in controlling the preferred orientation of GaN when grown on m-plane sapphire, but this intriguing dependence of preferred orientations on the experimental conditions is far from being scientifically understood
We employed both an epitaxial lateral overgrowth of GaN on SiO2-patterned m-plane sapphire substrates and ab initio density functional theory to investigate the determining factor of a preferred orientation of GaN domains when grown on m-plane sapphire substrates
It turned out that the brightness difference between divisions is closely related to site-dependent selection of preferred orientations of GaN domains, as discussed as follows

Summary

Results and Discussion

The unit cell of the mask pattern consists of 12 divisions as schematically shown in Fig. 1, which is a mosaic composite image obtained by joining together a series of optical microscopy images of epitaxially overgrown GaN. The works of separation were calculated to be 0.20 eV/Å2 and 0.18 eV/Å2 for the (11 ̄00) and (11 ̄03 ̄) orientation, respectively Their difference corresponds to ~4.3 eV when considered the size of the unit cell for the (11 ̄03) orientation, implying that the interface between (11 ̄00)-oriented GaN film and m-plane sapphire substrate may be energetically much more stable than that of (1103)-oriented one and the substrate. Our investigation revealed that the effective concentration of reacting species (Ga and N) played an important role in determining a preferred orientation of GaN domains grown on m-plane sapphire substrates. Our computational simulation disclosed that the preferred orientation of GaN grown on m-plane sapphire changes from (1103) to (1100) due to the crossover of the relative formation energy at a very low coverage of Ga and N species, is consistent with the experimental observation

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