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SEMICONDUCTORS AND NANOSTRUCTURES 2009Spin polarization of carriers in a GaAs/GaAlAs resonant tunneling diodeSpin polarized carrier systems are of interest particularlywith a view to polarized spin injection for giant magnetotoresistance(GMR) devices and spintronics applications.However, for various physical reasons, spin polarized injectionis in general difficult to achieve in real devices. Herewe show that it is possible to monitor the spin polarizationof carriers throughout a resonant tunneling diodes using polarizationresolved micro-photoluminescence.We have investigated the spin polarization of carriersin asymmetrical n-i-n GaAs/GaAlAs resonant tunnelingdiodes (RTD) by analyzing the polarized resolved photoluminescencefrom both GaAs quantum well (QW) and contactlayers under applied voltage and magnetic field. Forthe measurements a micro-photoluminescence setup with alow temperature x − y − z displacement stage was used tosimultaneously perform transport and photoluminescenceon single RTD etched mesa structure. Figure 67 shows aschematic band diagram of our device under forward biasvoltage, light excitation, and magnetic field parallel to thetunnel current. Under applied bias, the photo-generatedholes from the top contact can tunnel through the structureand recombine with electrons into the QW and contact layers.Figure 68 presents typical polarized resolved photoluminescencespectra at 0.195 V bias voltage. The higher energyemission peak (∼ 1.605 eV) is attributed to the fundamentalquantum well (QW) transition whereas the emissionaround 1.52 eV is due to various optical transitions in thecontact layers including the indirect recombination betweenfree holes and electrons in the two dimensional electron gas(h-2DEG) formed at the accumulation layer (∼ 1.512 eV).charge density, filling factors and spin polarization of thetwo-dimensional gas formed in the accumulation layer.Figure 67: Schematic band diagram of our device under forwardbias, light excitation and magnetic field parallel to the tunnel current.Figure 68: A representative photoluminescence spectra from theQW and contact layers measured at B = 19 T and T = 4.2 K.In a magnetic field the photoluminescence from the QWand contact layers shifts to higher energies and shows oscillationsin intensity (not shown). Figure 69 shows themagnetic field dependence of circular polarization degreefrom the QW, contact layers (total PL spectra) and fromthe h-2DEG emission. The polarization of the carriers,P = (I σ+ −I σ− )/(I σ+ +I σ− ), can be obtained from the integratedintensity of the polarization resolved photoluminescence.We have observed that the QW emission presentsnegative polarization degree up to 55% which oscillateswith magnetic field. A similar behavior is observed for theemission from the GaAs contact layers.To further understand this data we are currently in the processof modeling the spin polarization of carriers in thestructure taking into account the carrier tunneling, carrierFigure 69: Magnetic field dependence of spin polarization of theQW, GaAs contact layers and from the h-2DEG emissions.J. Kunc, M. Orlita, D. K. MaudeY. Galvão Gobato, L.F. dos Santos (Federal University of São Carlos, Brazil), M. Henini (School of Physics and Astronomy,University of Nottingham, UK)50