We present Raman spectra obtained from very short period (a few atomic layers) GaAs/AlAs superlattices with asymmetrical unit cells containing two different GaAs wells. This allows us to analyze quantitatively for the first time the atomic‐scale component of the interface roughness. We demonstrate that it mainly originates at the GaAs on AlAs interface and strongly decreases with the growth temperature and the underlying AlAs layer thickness.

Atomic‐scale roughness of GaAs/AlAs interfaces: A Raman scattering study of asymmetrical short‐period superlattices

Interface roughness from Γ and X luminescence in type II GaAs superlattices with compisition gradient

We study raman scattering by acoustic phonons in semiconductor superlattices and multiple quantum wells and show that it allows novel access to growth-related and intrinsic material properties. In the ideal superlattice the acoustic-phonon dispersion is backfolded and gaps appear at edge and center of the mini-Brillouin zone. Raman spectra show doublets of folded acoustic phonons with a fixed transfer of crystal momentum. In real superlattices interface roughness and layer thickness fluctuations cause Raman scattering with phonons for which crystal-momentum conservation is partially relaxed. Under resonant excitation we observe continuous emission which reflects features of the folded-phonon density of states such as internal and zone-edge dispersion gaps. From these features we determine the lateral extent of interface growth islands. The resonance behavior of folded-phonon scattering and continuous emission depends on homogeneous and inhomogeneous broadenings of the electronic structure which we determine separately. From the temperature dependence of these effects we obtain information on electron-phonon coupling constants in two-dimensional systems.

Raman scattering by acoustic phonons in semiconductor superlattices

The lattice dynamics of superlattices is now very well understood and most of the theoretical predictions have been quantitatively verified by Raman scattering, at least on GaAs/AlAs structures. This system is particularly interesting for several reasons: 


samples are currently available at a very high and controlled quality,


phonon dispersion curves in the bulk constituents GaAs and AlAs are known,


almost perfect lattice matching is achieved,


GaAlAs alloy lattice dynamics is well described by reasonably simple models.

Confinement and Disorder Effects on Phonons in Semiconductor Microstructures

The lattice dynamics of superlattices based on two different pure constituents, like for instance GaAs/AlAs, InAs/GaSb or Si/Ge, is now very weL.L. understood and most of the theoretical predictions have been successfully verified by Raman scattering, at least on GaAs/AlAs structures which are available at a very high quality1.

Daniel Paquet

Papers

The influence of interface disorder on the electronic structure of a quantum well: A theoretical study