Development of an optically gated $\mathrm{Fe}/n\text{-GaAs}$ spin-polarized transistor

Efficient modulation of electrically injected spin signals that is suitable for modern-day transistor functionality is yet to be established. In this work, we demonstrate in detail the fabrication of a $\mathrm{Fe}/n\text{-GaAs}$ spin injection device and the experimental setup for an optical gating of the nonlocal spin transport signal. In situ scanning electron microscopy interface imaging reveals more uniform current distribution at the $\mathrm{Fe}/n\text{-GaAs}$ injector interface at bias voltages higher than the Schottky barrier height. Three- and four-terminal Hanle measurements confirm successful spin injection into $n$-GaAs, with strong interfacial spin dephasing at high magnetic fields. A time-resolved pump-probe Kerr rotation setup was used to illuminate circularly polarized light in the region of the pure spin current in $\mathrm{Fe}/n\text{-GaAs}$ lateral spin injection devices, where ($0.4\pm 0.3)\%$ modulation of the nonlocal signal depending on the light helicity was observed at 30 K.

Figure 1

RHEED (15 keV) images of (a) GaAs(001) after $800{}^{\circ }\mathrm{C}$ anneal and (b) 5-nm deposition of Fe. (c) X-ray reflection measurement of a GaAs/Fe/Au film stack. (d) Scanning electron microscope image of a fabricated four-terminal device.

Figure 2

(a) Three-terminal current-voltage relation of the Fe/GaAs interface of the injection contact (2) as measured at 4 K. (b) In situ SEM interface image of the spin-valve device with an injection current $I_{2-1}$ of −125 μA where two images with 3.0- and 2.5-kV electron-beam deceleration voltages are subtracted to highlight the interface. The yellow and the green rectangles indicate the regions used for contrast deviation analysis of the injector and drain contact, respectively. (c) The injection current $I_{2-1}$ dependence of the ratio of contrast deviations between the injector (2) and the drain (1) contact, ${\sigma }_2/{\sigma }_1$, and the interface voltage $V_{2-4}$. (d) Three- and four-terminal Hanle voltages (with offset voltages of −0.137 V and −2.32 mV, respectively) measured with −100 μA injection current at 4 K.

Figure 3

(a) Wavelength dependence of time-resolved Kerr rotation signals in $n$-GaAs at 30 K. (b) Numerical fit of 822-nm Kerr response to Eq. (2).

Figure 4

(a) Schematic of the optical gating in nonlocal spin injection devices. (b) The optical micrograph of our device in the optical cryostat used for the time-resolved Kerr measurements. The red circle indicates the region of the circularly polarized light excitation. (c) Nonlocal voltage (measured between the contacts 3 and 4 with $I_{\mathrm{inj}}=-100\mu \mathrm{A}$ at 30 K) with the clockwise (red) and the counterclockwise (blue) circular polarizations and the linear polarization (black). (d) Optical modulation efficiency, defined as the percentage ratio of the difference and the sum of the nonlocal voltages with the clockwise and the counterclockwise circular polarization, $\left(V_{3-4,\sigma +}-V_{3-4,\sigma -}\right)/\left(V_{3-4,\sigma +}+V_{3-4,\sigma -}\right)$, against the laser power.