EXCITONIC MODEL FOR 2ND-ORDER RESONANT RAMAN-SCATTERING

A theoretical model for second-order resonant Raman scattering is pres ented. The effect of Coulomb interaction between electrons and holes i s fully taken into account in the framework of the effective-mass appr oximation. By introducing discrete and continuous excitonic intermedia te states in the Raman process, an explicit expression for the Raman s cattering efficiency is given for long-range Frohlich electron-phonon interaction. The model developed can be used to evaluate Raman profile s around the resonant region. A closed-form expression for all matrix elements of the exciton-phonon interaction is obtained once the Coulom b problem for the relative electron-hole motion is separated in spheri cal coordinates. For the first time, to our knowledge, transitions bet ween states from the excitonic ionization continuum for nonzero phonon wave vectors are exactly included in the calculations. The dependence of the Raman scattering efficiency on electron and hole masses is ana lyzed. The contribution of the different excitonic transitions to the scattering process is also studied. Finally, the model is compared to available experimental data for GaP, InP, GaAs, and GaSb. The overall agreement with the measured resonance profiles and their absolute scat tering efficiencies confirms that excitonic effects are required for a satisfactory interpretation of these phenomena.