Electronic and vibronic structure of the (GaAs)1(AlAs)1superlattice

Abstract

Resonant Raman scattering has been observed in (GaAs${)}_1$(AlAs${)}_1$ superlattices (one layer of GaAs alternating with one layer of AlAs) for the excitations in the region of the optical phonons of AlAs and GaAs with use of laser photon energies around 1.9 and 2.1 eV. With the help of linear muffin-tin-orbital (LMTO) band-structure calculations these resonances are attributed to transitions from the GaAs-like top of the valence band to the folded $X_3$ conduction band of AlAs and to the ${\Gamma }_1$ GaAs-like conduction band. The Raman spectra reveal longitudinal phonons propagating perpendicular to the superlattice planes and also, around the 1.9-eV resonance, satellites of these phonons shifted slightly to higher frequencies. These satellites are tentatively attributed to random inversion of Al-Ga pairs, i.e., to imperfections of the superlattice.