A study of the vertical transport of electrons in (GaAs)_n(AlAs)_msuperlattices by Fourier transform infrared spectroscopy

Abstract

The longitudinal optical vibrational modes have been studied in (GaAs)n(AlAs)m superlattices by means of FTIR spectroscopy. In the undoped samples, confined LO phonons have been observed; the dispersion of LO phonons obtained by FTIR spectroscopy was in good agreement with the Raman data. In the doped (GaAs)n(AlAs)m superlattices, coupling of confined vibrational LO modes with superlattice plasmons has been found. Analysis of the experimental results showed that the frequency of superlattice plasmons in the superlattices studied is mostly determined by the population of the miniband formed by the Gamma -like conduction band states. The fitting of the calculated reflection spectra to the experimental spectra allowed us to measure the population of the minibands, the effective mass and the vertical mobility of electrons.