Optimization of Si/N Treatment Time of Sapphire Surface and Its Effect on the MOVPE GaN Overlayers

We report that the exposure of the sapphire substrate, prior to the deposition of a GaN nucleation layer, under simultaneous silane and ammonia flows fundamentally influences the quality of GaN epilayers grown by Metal-Organic Vapor Phase Epitaxy (MOVPE). This step of the growth process will be referred to as “Si/N treatment”. An increase of the interfacial energy between the GaN nucleation layer and sapphire, induced by this Si/N treatment, changes the morphology (2D to 3D) of this nucleation layer and results in improved quality for GaN epilayers. For an optimized Si/N treatment time (30 s), a 300 K electron mobility as high as 650 cm2/Vs was obtained. Using symmetric (0002) rocking curves, we measured 180 arcsec full width at half maximum (FWHM) in ω-scan. 9 K photoluminescence spectra are dominated by a sharp peak (FWHM = 3.5 meV) corresponding to donor bound exciton recombination.