Improvement of the optical properties of metalorganic chemical vapor deposition grown GaN on sapphire by an in situ SiN treatment

We have studied the effect of an in situ SiN treatment of sapphire substrates on the optical properties of GaN films grown by metalorganic chemical vapor deposition. The SiN deposition, partially covering the substrate, forms a mask for the formation of nanoscale auto-organized GaN islands. These islands formed upon an increase of the temperature after deposition of a GaN buffer layer on this mask. A photoluminescence study of the GaN epilayers obtained by lateral overgrowth of these islands shows significant enhancement of the luminescence emission intensity of the near band edge peaks and a reduction of the full width at half maximum of the donor bound exciton ((DX)-X-0) peak by 32% down to 4 meV compared to in our standard process. The GaN films grown using SiN treatment are highly stressed as evidenced by a blueshift of 10 meV in the (DX)-X-0 peak energies. Photoelectrochemical etching in aqueous solution of KOH was applied to reveal the dislocation density. The density of "whisker-like" etch features, which form due to the presence of dislocations, was reduced from 6x10(9) cm(-2) in standard GaN films to 8x10(8) cm(-2) in the GaN layers grown with the optimized SiN treatment. (C) 2001 American Institute of Physics.