Raman and photoluminescence studies of biaxial strain in GaN epitaxial layers grown on 6H-SiC

The effect of biaxial strain on optical phonons in high-quality GaN epitaxial layers grown on 6H-SiC substrates by metal organic chemical vapor deposition has been studied. The deformation potential constants for the E-2((1)), A(1)(TO), E-1(TO), and E-2((2)) optical phonon modes in hexagonal GaN have been obtained. A method for calculating strain in hexagonal GaN layers from Raman data alone is suggested. A comparative analysis of the strain measured by x-ray diffraction and Raman spectroscopy shows that these data agree well. It is found that the biaxial stress of 1 GPa results in a shift of the excitonic photoluminescence lines of 20 +/- 3 meV. (C) 1997 American Institute of Physics.