Epitaxy of GaN LEDs on large substrates: Si or sapphire?

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We present first results on the limits of GaN growth on large diameter sapphire and the challenges that have to be solved for a successful growth of high power LEDs on silicon substrates. Up to 5.4 μm thick crack-free GaN on Si(111) LED structures were grown by metalorganic chemical vapor phase epitaxy. The FWHM of the GaN (0002) ω scan in x-ray diffraction amounts to 380 arcsec. On Si substrates, we achieve low curvatures with radii > 50 m, which is important for a successful processing of the samples on large diameter substrates. Additionally, a low curvature during InGaN multi-quantum-well growth is achieved and enables the growth of homogenous InGaN layers. The main difficulty for GaN-on-Si is light extraction, which leads to an approximately three- to four-fold reduction in direct comparison with GaN LEDs on sapphire.