Vibrational properties and the miniband effect in InGaAs/InP superlattices

A. DE GIOVANNI RODRIGUEZ; J. C. GALZERANI; YU. A. PUSEP; D. M. CORNET; D. COMEDI; R. R. LAPIERRE

Erice, Sicilia

Simposio; EPIOPTICS-9, 39th Course of the International School of Solid State Physics; 2006

InGaAs/InP:Si superlattices (SL?s) of several periods were investigated using polarized Raman spectroscopy. In the long period SL, the translational symmetry was violated and the Raman selection rules were not observed. However, with the decrease of the barrier thicknesses, these rules became evident and considerable blue shifts f the LO modes are noticed, as a manifestation of the presence of coupled plasmon-LO phonon modes propagating normal to the layers in these short period SL?s. We here show that the observed effects can be attributed to the formation of a miniband energy structure. The good agreement between the frequencies of the measured InP-like coupled modes with the calculated ones confirms that the blue shifts of the longitudinal modes were observed due to the miniband effect. Further investigations led to the conclusion that the partial coherence length of the lattice vibrations for the long period SL is of the order of the size of the crystal unit cell; meanwhile, this parameter increases considerably for the short period SL?s, also in agreement with the emergence of the selection rules for the coupled vibrations in the later structure.