Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface

We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and $n$-GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport.

Figure 1

(a) Photomicrograph of the $\mathrm{Fe}/\mathrm{GaAs}$ device. The side contacts are used for the voltage measurements indicated by the labels. (b) Band diagram near the $\mathrm{Fe}/\mathrm{GaAs}$ interface under reverse bias (0.2 V), zero bias (0 V), and forward bias ($-0.2\mathrm{V}$). The inset shows the total ($V_{ab}$), drain ($V_{ac}$), source ($V_{eb}$), and channel ($V_{ce}$) voltage measurements when current flows from $a$ to $b$ at $T=10\mathrm{K}$.

Figure 2

(a) Voltage vs magnetic field for a current $I=0.8\mathrm{mA}$ flowing from $a$ to $b$. The source-drain voltage $V_{ab}\approx 0.5\mathrm{V}$. An offset is subtracted from each curve, and a slope due to the Hall effect has been subtracted from $V_{ac}$ and $V_{eb}$. The contacts are labeled in Fig. 1a. (b) Measurements for $I=0.8\mathrm{mA}$ flowing from $b$ to $a$. The peak at zero field appears only for measurements that include the drain contact.

Figure 3

(a) The source-drain voltage $\Delta V_{ab}$ is shown as a function of magnetic field and temperature. Solid lines are the results of the modeling explained in the text. (b) The Kerr rotation ${\theta }_K$ (proportional to $S_z$), measured near the source, is shown as a function of magnetic field for three temperatures. The solid curves are calculated using the same parameters used to fit the transport data.

Figure 4

(a) $\Delta V_{ab}$ vs magnetic field at $T=10\mathrm{K}$ for four different bias currents. Each curve is offset for clarity. The solid lines are the fitted curves using the model explained in the text. (b) $\Delta V_{ab}$ at $T=10\mathrm{K}$ and $I=2.0\mathrm{mA}$ for three different $n$-type samples.