Spin-dependent recombination in GaAs

Spin-dependent recombination (SDR) has been studied via photoluminescence of samples grown by molecular-beam epitaxy (MBE) consisting of many thin GaAs wells separated by thin AlGaAs barriers. The photoluminescent-intensity enhancement with circularly polarized optical pumping is observed to be as much as 46% above the intensity level seen with linearly polarized pumping. Electron-spin polarizations as large as 0.84 have also been generated. Similar but smaller effects are seen in the emission from the relatively thick GaAs buffer layer which is grown by MBE prior to the growth of the superlattice. The SDR and electron polarization $\rho$ of the multilayers and the GaAs buffer layer have been studied as a function of the pump intensity and a transverse magnetic field $B$ (Voigt-geometry-Hanle effect). Both pulsed and cw laser pump sources were used. It is observed that SDR is absent at very low pump intensities and generally goes through a maximum as the pump intensity is increased. In all cases, the decrease of SDR with $B$ is faster than that of $\rho$. It appears that these data cannot be adequately described quantitatively by the theory used earlier by others in a study of SDR in the donor-acceptor pair photoluminescence of ${\mathrm{Al}}_{0.4}$ ${\mathrm{Ga}}_{0.6}$As.