Polar optical-phonon modes are derived analytically for spheroidal quantum
dots with wurtzite crystal structure. The developed theory is applied to a
freestanding spheroidal ZnO quantum dot and to a spheroidal ZnO quantum dot
embedded into a MgZnO crystal. The wurtzite (anisotropic) quantum dots are
shown to have strongly different polar optical-phonon modes in comparison with
zincblende (isotropic) quantum dots. The obtained results allow one to explain
and accurately predict phonon peaks in the Raman spectra of wurtzite
nanocrystals, nanorods (prolate spheroids), and epitaxial quantum dots (oblate
spheroids).Comment: 11 page