Interface and confined polar optical phonons in spherical ZnO quantum dots with wurtzite crystal structure

We derive analytically the interface and confined polar optical-phonon modes for spherical quantum dots with wurtzite crystal structure. While the frequency of confined optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals are shown to have a discrete spectrum of frequencies different from those in bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO quantum dots are found to be in excellent agreement with experimental resonant Raman scattering data. The derived analytical expression for phonon modes can facilitate interpretation of experimental data obtained for ZnO quantum dots.