Optical phonons and resonant Raman scattering in II–VI spheroidal quantum dots

Abstract

AbstractFirst order and multiphonon resonant Raman scattering processes from confined and interface polar optical phonons in II–VI nanocrystallites are analyzed. Fröhlich interaction between excitons and optical phonons has been considered and general selection rules for the exciton–phonon matrix elements of the scattering processes in the case of spheroidal quantum dots are given. A comparison is made between the Raman selection rules and non‐linear hyper‐Raman selection rules for spherical dots. It is shown that the relative intensities between phonon overtones in II–VI spherical quantum dots can be correctly described in the framework of excitonic model and the optical polar vibrational continuum model satisfying both the mechanical and electrostatic matching conditions at the interface. Detailed discussions of the surface optical phonons are provided in the case of a spherical Quantum‐Dot/Quantum‐Well (QD/QW) heterostructure. Their frequency dependence on the geometry, material parameters, as well as the electron–phonon interaction Hamiltonian are also reported. In addition, the interface optical phonons and the corresponding electron–phonon interaction in nanostructures with prolate and oblate spheroidal geometries and their contribution to the first order scattering process have been studied. This surface‐optical phonon modes are strongly dependent on the nanocrystal geometry and new Raman selection rules are obtained given a plausible explanation for the observed low frequency shoulders present in the spectrum of several II–VI semiconductor nanostructures. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)