Doubly resonant first order Raman scattering in narrow quantum wells: Scattering mechanism and resonance profile

Optical Phonons in Superlattices

“…Experimental data on the modified phonon structure of SLs are almost exclusively due to Raman scattering. We have discussed three different experiments, one concerning scattering from confined phonons [55], and two concerning I F phonons, but carried out under different conditions [56,65]. In the confined phonon experiment [55] resonance profiles and selection rules for polarizations and confinement quantum numbers were studied simultaneously.…”

“…How can DP coupling cause depolarized scattering under the present conditions? In [55] the following answer has been given. A certain non-zero probability exists for excitons to recombine not immediately after phonon emission but only after an elastic scattering event from impurities or defects has taken place.…”

“…In [55] a GaAs/Al,,,,Ga,~,,As QW structure has been studied. It consists of three QWs of seven monolayers GaAs ( d , z 3 nm), separated by barriers of 102 nm thickness from each other, and by an alloy buffer layer of 1 pm from the GaAs substrate.…”

“…It holds in particular for the weak, polarized Raman peaks which are forbidden by theory. The fact [55] that they exhibit the same resonance behavior and the same allowed confinement numbers as polarized scattering suggests that the electron-phonon interaction mechanism should be the same in both cases. How can DP coupling cause depolarized scattering under the present conditions?…”

“…Note the resonance enhancement as indicated by the magnification values ( x 6, x25). Several confined LO (GaAs) phonon modes and the TO mode (weak structure) are resolved [55] forbidden. The strongest Raman peak occurs at the bulk LO phonon position.…”