LAUSR

Abstract GaAs/AlGaAs multi quantum well (QW) architecture is employed to study the optical injection of spin polarized electrons in Al0.22Ga0.78As material over the excitation energy range of 1.85–3.4 eV. By analyzing the degree of circular polarization (DCP) of photoluminescence from QW, it is seen that though the magnitude of DCP is affected by the QW thickness, its spectral dependence is mainly governed by the barrier layer. In addition to a usual maximum in DCP near Γ-point, a local maximum at 3.2 eV is also observed. This is identified as a signature of optical spin orientation in the L-valley of AlGaAs. The comparison of DCP spectra with that of a ZrO2 coated structure confirms that its origin is deep rooted in the bulk material and is therefore robust against surface treatments. A two level model for the transfer of spin polarized electrons from L to Γ valley is proposed to estimate the spin relaxation time of electrons which is found to be large in the L-valley of AlGaAs when compared with GaAs. This could be an interesting aspect for the fabrication of AlGaAs based spintronic devices. Further the QW architecture proposed here is useful for studying the injection of spin polarized carriers in indirect bandgap semiconductors.