In contrast to the most commonly studied nanocrystals of II-VI materials, resonant Raman spectra of colloidal III-V quantum dots (QDs) show two almost equally intense peaks centered approximately at the longitudinal and transverse optical (TO) bulk phonon frequencies. The “anomalous” spectra of III-V QDs are explained in the framework of a microscopic theory for the first-order resonant Raman scattering, which takes into account the optical deformation potential (ODP) and Fröhlich exciton-phonon interactions—valid for spherical nanoparticles. It is obtained that: (i) the “anomalous” TO peak is mostly due to confined phonon modes with the angular momentum $l_p=3$; (ii) Raman intensity depends on the QD radius $\left(R\right)$ as $R^{-3}$ for the ODP mechanism, while for the Fröhlich one it is proportional to $R^{-1}$; and (iii) the relative intensity $I_{\text{TO}}/I_{\text{LO}}$ ratio value is higher in backscattering configuration for cross polarization than for parallel one. Raman spectra calculated within the Luttinger-Kohn Hamiltonian for the electronic states and a phenomenological theory of optical vibrations including rigorously both the mechanical and electrostatic matching boundary conditions explain the experimental data for InP QDs using bulk phonon parameters and ODP constant.

• Received 2 June 2008

DOI:https://doi.org/10.1103/PhysRevB.78.081304