Angular and mode distribution of acoustic phonon emission by hot 2D electrons in GaAs: the effect of acoustic anisotropy and screening

Abstract

We report a detailed theoretical study of the angular and polarization dependence of the acoustic phonon emission by a hot two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterojunctions and quantum wells (QW) and compare the results with some recent heat pulse measurements. We use a model which not only includes the dynamical screening of electron–phonon interaction but also takes proper account of the finite “thickness” of the 2D gas and above all, considers the strong acoustic anisotropy of the electron–phonon matrix elements and the propagation process. For QW with different widths we demonstrate the strong dependence of the angular distribution on the well width. For heterostructures in the (0 0 1)-plane, we can explain, in contrast to earlier theoretical studies, the phenomena of missing longitudinal modes for phonon emission close to the two-dimenional electron gas (2DEG) normal.