A STUDY OF THE VERTICAL TRANSPORT OF ELECTRONS IN (GAAS)N(ALAS)M SUPERLATTICES BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The longitudinal optical vibrational modes have been studied in (GaAs) n(AlAs)m superlattices by means of FTIR spectroscopy. In the undoped s amples, confined LO phonons have been observed; the dispersion of LO p honons obtained by FTIR spectroscopy was in good agreement with the Ra man data. In the doped (GaAs)n(AlAs)m superlattices, coupling of confi ned vibrational Lo modes with superlattice plasmons has been found. An alysis of the experimental results showed that the frequency of superl attice plasmons in the superlattices studied is mostly determined by t he population of the miniband formed by the GAMMA-like conduction band states. The fitting of die calculated reflection spectra to the exper imental spectra allowed us to measure the population of the minibands, the effective mass and the vertical mobility of electrons.