Highly Spin-Polarized Room-Temperature Tunnel Injector for Semiconductor Spintronics using MgO(100)

The spin polarization of current injected into GaAs from a $\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}/\mathrm{M}\mathrm{g}\mathrm{O}(100)$ tunnel injector is inferred from the electroluminescence polarization from $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum well detectors. The polarization reaches 57% at 100 K and 47% at 290 K in a 5 T perpendicular magnetic field. Taking into account the field dependence of the luminescence polarization, the spin injection efficiency is at least 52% at 100 K, and 32% at 290 K. We find a nonmonotonic temperature dependence of the polarization which can be attributed to spin relaxation in the quantum well detectors.

Figure 1

TEM image of the $\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}/\mathrm{M}\mathrm{g}\mathrm{O}$ spin injector (a) and electroluminescence (EL) spectrum of samples I (b) and II (c). The thin and thick lines in (b) and (c) represent the left ($\sigma +$) and right ($\sigma -$) circular polarization components of EL, respectively.

Figure 2

Magnetic field dependence of $P_{\mathrm{E}\mathrm{L}}$ [(a) and (b)] and $P_C$ [(c) and (d)] for sample I at 100 K and sample II at 290 K (open circles). The crosses in (a) are $P_{\mathrm{E}\mathrm{L}}$ of a control sample with a Pt electrode. The solid lines in (c) and (d) show the field dependence of the CoFe moment measured with a SQUID magnetometer at 20 K, which has been scaled to allow comparison with $P_C$.

Figure 3

Bias and temperature dependence of $P_C$ of samples I (a) and II (b). Note the different bias ranges for (a) and (b).

Figure 4

Temperature dependence of the EL polarization of samples I (a) and II (b). The open and closed squares correspond to values of $P_{\mathrm{E}\mathrm{L}}$ at 5 T and of $P_C$, respectively. Note the different temperature ranges for (a) and (b). The inset of (a) shows the $I\mathrm{\text{−}}V$ curves of sample I at various temperatures.