STUDY OF PHONONS IN SEMICONDUCTOR SUPERLATTICES BY RAMAN-SCATTERING SPECTROSCOPY AND MICROSCOPIC MODEL CALCULATION

Raman spectroscopy is used to study phonons in a series of thin (AlAs) (m)/(GaAs)(n) superlattices (SLs) grown by molecular beam epitaxy (MBE ). The influence of buffer layer type on the interface roughness of he terostructures is carefully evaluated. The accuracy of optical phonons and the degree of peak sharpness of GaAs-like confined modes are exam ined via off-resonance Raman spectroscopy. Theoretical calculations of phonons in thin (AlAs)(m)/(GaAs)(n) superlattices (i.e. samples with m, n less than or equal to 12) are reported for various directions of propagation by using a rigid-ion model. Optical phonons acquire signif icant dispersive character when the wavevector q forming an angle thet a with the growth axis of the superlattice is changed from theta = 0 t o pi/2, i.e. from [001] to [100]. The frequency gaps in the angular di spersions due to mode anti-crossing behavior observed recently by Zunk e et al. using micro-Raman spectroscopy and studied by a continuum mod el are found to be in reasonably good agreement with our lattice dynam ical model calculations. (C) 1997 Elsevier Science S.A.