Reversal of spin polarization direction in excitonic photoluminescence of AlGaAs

Abstract

An anomalous reversal of the direction of exciton spin polarization is found in an optical-orientation study of AlxGa1−xAs alloys. A negative degree of circular polarization of excitonic photoluminescence is observed in direct-gap AlGaAs under excitation with circularly polarized light with the photon energy lying in a narrow range just above the free-exciton transition. The resonant switching of the polarization direction is attributed to the effect of the minor residual strain in the epitaxial film that results in lifting of the degeneracy of the lightand heavy-hole sub-bands. The electron g-factor is estimated from combined time-resolved and Hanle-effect data and amounts to 0.056-0.086 for x = 15% alloy.

Optical tailoring of carrier spin polarization in Ge/SiGe multiple quantum wells

“…Our results indeed suggest the close similarity of the zone center band structure between Ge and III-V compounds, in which such polarization inversion above LH threshold has been observed. 15,16 It is worth noticing that such finding differs from recent tight-binding calculations, 17 where no inversion in the spin orientation of electrons created upon light absorption in the C valley of the CB has been predicted. Although our samples present slightly different strain level and composition of the barriers with respect to those considered in Ref.…”

Electron spin orientation under in-plane optical excitation in GaAs quantum wells

“…In many cases, spin-polarized electrons are both optically excited and optically detected. [3][4][5] Other approaches combine optical excitation of spin-polarized carriers with electrical detection schemes utilizing, e.g., orientation-and spin-dependent charge currents. 6 Still others employ electrical injection of spin-polarized carriers, e.g., via paramagnetic semiconductors as spin aligners, and probe optically by polarization-resolved photoluminescence (PL) spectroscopy.…”