Interferometric Detection of Spin-Polarized Transport in the Depletion Layer of a Metal-GaAs Schottky Barrier

It is shown that the Kerr rotation of spin-polarized electrons is modulated by the distance of the electrons from the sample surface. Time-resolved Kerr rotation of optically excited spin-polarized electrons in the depletion layer of $n$-doped GaAs displays fast oscillations that originate from interference between the light reflected from the semiconductor surface and from the front of the electron distribution moving into the semiconductor. Using this effect, the dynamics of the photogenerated charge carriers in the depletion layer of the biased Schottky barrier is measured.

Figure 1

(a) Scheme of a sample with a spacer layer ($n_1$) and a spin-polarized layer ($n_2$). A probe beam is reflected at the sample surface ($r_1$) and at the boundary to the spin-polarized layer ($r_2^{+}$ and $r_2^{-}$). (b) Complex-plane representation of reflection amplitudes and KR angle $\theta$. (c) Measured $\theta (\Delta t)$ in $n$-doped GaAs (sample 1) with an applied bias of $-1.0\mathrm{V}$ (solid line) and $-1.1\mathrm{V}$ (dashed line) across the Schottky barrier. Oscillations in $\theta$ are due to the displacement of the spin-polarized electron front into the semiconductor.

Figure 2

Measured $\theta$ on sample 1. (a) Map of $\theta$ vs $\Delta t$ and $U$ at $B=0\mathrm{T}$ and $650\mu \mathrm{W}$ pump power. (b) Dependence of $\theta$ vs $\Delta t$ on pump power at $U=0\mathrm{V}$. (c) Same as (a) with $B=1\mathrm{T}$.

Figure 3

(a) Measured $\theta$ vs $\Delta t$ at $B=0$ (solid lines) and 8 mT (dashed lines) and for $U=300$ and 550 mV (sample 1). In (b), $\theta$ vs $B$ at $\Delta t=12.4\mathrm{ns}$ shows resonant spin amplification at both $U=300$ and 550 mV, with opposite signs for the two cases.

Figure 4

(a) Measured $d$ vs $\Delta t$ for sample 1 and $650\mu \mathrm{W}$ pump power, with $U$ varying between $-2$ and 0.5 V in 0.5 V steps; lines are fits as described in the text. In (b), $d-d_0$ vs $U$ at $\Delta t=2.3\mathrm{ns}$ is plotted for samples 1 (solid diamonds) and 2 (open diamonds) together with fits of the depletion-layer thickness $d_{\mathrm{depl}}$ (lines).