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Single-crystal gallium nitride (GaN) thin films were grown using a graphene mask via multiple epitaxial lateral overgrowth (multiple-ELOG). During the growth process, the graphene mask self-decomposed to enable the emergence of a GaN film with a thickness of several hundred nanometres. This is in contrast to selective area growth of GaN using an SiO2 mask leading to the well known hexagonal-pyramid shape under the same growth conditions. The multiple-ELOG GaN had a single-crystalline wurtzite structure corresponding to the crystallinity of the GaN template, which was confirmed with electron backscatter diffraction measurements. An X-ray diffraction rocking curve of the asymmetric 102 reflection showed that the FWHM for the multiple-ELOG GaN decreased to 405 from 540′′ for the underlying GaN template. From these results, the self-decomposition of the graphene mask during ELOG was experimentally proven to be affected by the GaN decomposition rather than the high-temperature/H2 growth conditions.

We have demonstrated the effect of p-GaN hole concentration on a graphene current spreading layer (CSL) for stabilization and improved performance of a near-ultraviolet light-emitting diode (NUV LED). While NUV LEDs with a more lightly-doped p-GaN showed poor electrical and optical properties and unstable performance, NUV LEDs with more heavily-doped p-GaN (∼2 × 1017 cm−3) showed very stable, outstanding performance. The main factor of the improvement was the enhanced contact property between the graphene CSLs and the p-GaN that resulted from the increase of the hole concentration, which led to a thinner barrier and an enhanced current injection. From our results, we were able to determine that hole concentration as heavy as 2 × 1017 cm−3 in p-GaN layers is a primary condition in NUV LEDs with graphene-based CSLs.