INCIDENT-PHOTON ENERGY-DEPENDENCE OF RAMAN-SCATTERING PROFILES BY FOLDED ACOUSTIC PHONONS IN GAAS ALAS SUPERLATTICES/

We present experimental and theoretical studies of the intensity of th e upper frequency mode relative to the lower one in the doublet Raman band of the first-folded longitudinal-acoustic phonon, I(+ 1)/I(- 1), as a function of an incident-photon energy in (GaAs)m(AlAs)m superlatt ices with m = 8, 10, and 12 monolayers. It is found experimentally tha t the value of I(+ I)/I(- 1) depends on the energy of an incident Ar+- laser line from 4765 to 5145 angstrom. Here, on the basis of an effect ive-mass approximation for the electronic structures and an elastic co ntinuum approximation for the phonon modes, we propose a simplified fo rmula for the incident-photon energy dependence of I( + 1)/I( - 1), ra ther than considering all the quantum processes of electron-photon and electron-phonon interactions. The calculations indicate that the expe rimental results are mainly due to resonant effects of the electronic transitions between the second subbands of electrons and holes.