Phonons in a strained hexagonal GaN-AlN superlattice

A GaN (6.3 nm)- AlN (5.1 nm) superlattice, grown by molecular beam epitaxy on a sapphire substrate and an AlN buffer layer, has been studied by means of micro-Raman spectroscopy. Most of the observed features have been identi fied and assigned to optical phonons of the superlattice layers. The averag e biaxial strain in GaN layers has been deduced from the detailed analysis of the frequency shift observed on the phonon lines. Additional measurement s on the bevelled sample clearly suggest the significant increase of this s train for decreasing distances from the interface with the buffer layer. (C ) 1999 American Institute of Physics. [S0003-6951(99)04105-4].