Anisotropy and energy dependence of the linear polarization of hot electron luminescence from GaAs quantum wells

Abstract

Hot electron luminescence (HEL) from p-doped GaAs and quantum wells shows a series of peaks corresponding to discrete LO-phonon losses. Much of the width of the zero-phonon loss peak arises directly from the initial-state valence band warping, so the HEL energies within the peak can be associated with specific k-directions. The degree of linear polarization (DoLP) varies over the width of the peak, so different k-directions can be identified with different polarizations. We present measurements of this polarization anisotropy for a series of quantum wells, together with model calculations in the diagonal approximation that the acceptor wavefunction is dominated by heavy hole states along the ⟨11⟩ directions, and in the spherical approximation that other directions contribute substantially. The data allow the diagonal approximation to be discarded. In contrast to the case for bulk material, the DoLP increases strongly with the initial photoexcitation energy. Previous calculations, averaging the DoLP over the HEL peak, underestimate this by a factor of nearly two. We show that the DoLP anisotropy requires comparison with calculations along high symmetry directions to obtain good agreement with the data.