Strongly bias-dependent spin injection from Fe into $n$-type GaAs

We report electrical spin injection into an $n$-doped GaAs $(N_d=1\times {10}^{18}{\mathrm{cm}}^{-3})$ region from an Fe thin film grown by molecular beam epitaxy. The spins are injected through an $n\text{−}{\mathrm{Al}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}$ Schottky barrier on a spin light emitting diode. Spin injection is detected optically via carrier recombination in the layer immediately adjacent to the Schottky barrier, allowing the spin transport to be studied through this important region of interest. A pronounced dependence of injected spin polarization upon applied bias voltage reveals that efficient spin injection occurs across a range of $\sim 1\mathrm{V}$, dropping off sharply to zero at all temperatures. At bias voltages higher than that at which the maximum spin injection occurs, the Schottky barrier resistance is lowered, accompanied by hot electron spin transport in the semiconductor.

Figure 1

(Color online) (a) The self-consistent field calculated band diagram for the structure showing the conduction $\left(E_c\right)$ and valence $\left(E_v\right)$ bands. (b) The room temperature LED electroluminescence spectra at increasing bias voltages. The inset shows the current-voltage characteristic. The recombination takes place in the $n\text{−}\mathrm{Ga}\mathrm{As}$ bulk region.

Figure 2

(Color online) (a) Oblique Hanle effect in the spin LED at $77\mathrm{K}$. The effective spin lifetimes $\left(T_s^{*}\right)$ are estimated from fits to Bloch theory outlined in the text. (b) Oblique Hanle effect at $300\mathrm{K}$.

Figure 3

(Color online) (a) The current-voltage characteristics of the spin LED at the temperatures and voltage bias ranges of interest. (b) Bias dependent spin injection at 300 and $77\mathrm{K}$, the plotted polarization $\left(P\right)$ represents the raw optical polarized signal from the recombination in the $n\text{−}\mathrm{Ga}\mathrm{As}$ layer. (c) The bias dependent polarization at $5\mathrm{K}$ showing the change in sign due to magnetic field reversal.