Photoluminescence studies of GaN films on Si(111) substrate by using an AlN buffer control

The optical properties of GaN epitaxial layers grown on silicon (111) substrates with AIN buffer layers by using metalorganic vapor phase epitaxy were investigated for various values of the buffer layer's thickness. As the AIN thickness increased, the peak position of the free exciton of the GaN films was red-shifted linearly and the full width at half maximum (FWHM) of the free-exciton peak decreased. The red-shift of the free-exciton peak was attributed to cracks due to heavy stress. In 80-nm-thick AIN, the strong band-edge emisson of GaN on Si (111) was observed with the full width at half maximum of the bound exciton line being as low as 17 mev at 13 K. The variations of Varshni's fitting parameter and the activation energy of the free exciton with the AIN thickness were evaluated for GaN films.