Magnetized Plasma in Polar Semiconductors

Abstract

Plasma excitations in metallic n-type GaAs are studied in high-magnetic fields using the method of inelastic light scattering (the Raman scattering). Experimental data are analyzed using a standard, dielectric function theory. The results obtained for samples with a high electron concentration are well understood in terms of longitudinal excitations. A strong interaction of coupled longitudinal optical-phonon-plasmon modes with the collective cyclotron resonance excitations (the Bernstein modes) is observed. In samples with a lower electron concentration, the unexpected feature in the vicinity of the undressed optical phonon is observed at high magnetic fields. This effect is explained in terms of transverse excitations, which would appear in the Raman spectrum due to disorder-activated selection-rule breaking. A field induced metal-insulator transition and magnetopolaron effect on shallow donors in GaAs is shown to be traced with the Raman scattering experiments in samples with the lowest electron concentration.