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 deposit ion of a GaN nucleation layer, under simultaneous silane and ammonia flows fundamentally influences the quality of GaN epilayers grown by Metal-Organi c Vapor Phase Epitaxy (MOVPE). This step of the growth process will be refe rred to as "Si/N treatment". An increase of the interfacial energy between the GaN nucleation layer and sapphire, induced by this Si/N treatment, chan ges the morphology (2D to 3D) of this nucleation layer and results in impro ved quality for GaN epilayers. For an optimized Si/N treatment time (30 s), a 300 K electron mobility as high as 650 cm(2)/Vs was obtained. Using symm etric (0002) rocking curves, we measured 180 arcsec full width at half maxi mum (FWHM) in omega-scan. 9 K photoluminescence spectra are dominated by a sharp peak (FWHM = 3.5 meV) corresponding to donor bound exciton recombinat ion.