Interaction of optical and interface phonons and their anisotropy in GaAs/AlAs superlattices: Experiment and calculations

Abstract

The angular anisotropy of interface phonons and their interaction with optical phonons in (001) GaAs/AlAs superlattices are calculated and experimentally studied. Experiments were performed by Raman light scattering in different scattering geometries for phonons with the wave vector directed normally to the superlattice and along its layers. Phonon frequencies were calculated by the extended Born method taking the Coulomb interaction into account in the rigid ion approximation. Raman scattering spectra were calculated in the Volkenshtein bond polarizability approximation. Calculations confirmed that the angular anisotropy of phonons observed in experiments appears due to interaction (mixing) of optical phonons, in which atoms are mainly displaced normally to superlattices, with interface phonons (TO-IF modes). In the scattering geometry, when the wave vector lies in the plane of superlattice layers, the mixed TO-IF modes are observed under nonresonance conditions. The Raman spectra for TO-IF modes depend on the mixing of atoms at heteroboundaries.

Phenomenological model for Raman spectra calculating based on “bond charge” taking into account deformation and electro‐optical mechanisms, including Fröhlich scattering

“…Second, it is known that in SL, the interfaces between the layers are not ideally flat. Both surface reconstruction (e.g., Volodin et al 7 ) and random mixing of gallium and aluminum atoms at the heterointerface take place. For example, Figure 6B shows the calculated spectra of GaAs 5 /AlAs 5 SLs with a primitive cell of 10 per 10 interatomic distances in the XY plane.…”

“…This made it possible to illuminate the SL from the "edge" and apply a geometry in which the wave vectors of the incident and scattered photons lie in the SL plane (the so-called "in-plane" geometry 9,10 ). This approach is also described in Volodin et al 7,8 To study the photoluminescence spectra of SLs, a solid-state laser with a wavelength of 442 nm was used.…”

“…Previously, to calculate the eigenwavenumbers and eigenvalues of phonons, we used the extended Born model taking into account the Coulomb interaction in the “rigid ions” model 6–8 . This made it possible to calculate the Raman spectra only taking into account the deformation mechanism 6–8 .…”

“…Previously, to calculate the eigenwavenumbers and eigenvalues of phonons, we used the extended Born model taking into account the Coulomb interaction in the "rigid ions" model. [6][7][8] This made it possible to calculate the Raman spectra only taking into account the deformation mechanism. [6][7][8] In the present work, to calculate the eigenwavenumbers and eigenvalues of phonons, the adiabatic "bond charge" (BC) model was used.…”

“…[6][7][8] This made it possible to calculate the Raman spectra only taking into account the deformation mechanism. [6][7][8] In the present work, to calculate the eigenwavenumbers and eigenvalues of phonons, the adiabatic "bond charge" (BC) model was used. This made it possible to include the electro-optical mechanism in the calculations, as well as to take into account the Fröhlich scattering.…”