Lattice dynamics of short‐period AlN/GaN superlattices: Theory and experiment

We report on the first observation of folded acoustic phonons in the Raman spectra of short-period AlN/GaN superlattices (SLs). The values of longitudinal and transverse sound velocities along the [0001] direction of SL were estimated. It is shown that the SL period can be evaluated from Raman data with a good accuracy. Ab initio calculations of the zone-center phonons in (AlN)n(GaN)n SLs with the number of monolayer equal to n = 2,4,6 were performed. The frequencies of phonon modes were calculated and the mode displacement patterns have been established. The theoretical Raman spectra were simulated and compared with experimental ones. A strong sensitivity of A1(LO) phonons confined within the AlN layer to its thickness was revealed both experimentally and in calculations. This finding can be used for quantitative characterization of short-period AlN/GaN SLs.