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Optic and Acoustic Phonons in Strained Hexagonal GaN/AlGaN Multilayer Structures

The effects of the layer thickness and alloy composition on the Raman spectra of hexagonal GaN/Al x Ga 1-x N multilayer structures have been investigated. Our findings show that the A 1 (TO) optic mode can be regarded as propagating through the structure, whereas other optic modes are confined to the GaN or Al x Ga 1-x N layer. We report the first observation of folded acoustic modes in short-period GaN/Al x Ga 1-x N superlattices. The dispersion of the LA phonon branch was determined by using different Raman scattering configurations. The sound velocity for GaN/Al x Ga 1-x N SL with Al content x = 0.28 was found to be 8410 m/s.