Electrical spin injection and transport in germanium

We report the first experimental demonstration of electrical spin injection, transport, and detection in bulk germanium (Ge). The nonlocal magnetoresistance (MR) in n-type Ge is observable up to 225 K. Our results indicate that the spin relaxation rate in the n-type Ge is closely related to the momentum scattering rate, which is consistent with the predicted Elliot-Yafet spin relaxation mechanism for Ge. The bias dependence of the nonlocal MR and the spin lifetime in n-type Ge is also investigated.

Figure 1

(a) Schematic atomic configuration of the Fe/MgO/Ge junction, showing 45 degree rotation of the MgO unit cell with respect to that of Ge. (b) A schematic diagram of the device structure and the nonlocal measurement scheme. The center-to-center distances between the spin injector and detector are 420 nm and 1 μm for devices A and B, respectively. (c) A SEM image of device A. The widths of the injector (E2) and detector (E3) are 400 nm and 250 nm, respectively. (d) Temperature-dependent I-V curves measured between spin injector (E2) and E1.

Figure 2

(a) Nonlocal spin valve signal measured on device A at 4 K with a DC injection current of −20 μA and AC injection current of −10 μA. The blue arrows indicate the magnetization directions of the injector and detector. (b) Temperature-dependent nonlocal spin valve signals on device A. The curves are offset for clarity. (c) and (d) Temperature-dependent nonlocal MR (Δ$R_{\mathrm{NL}}$) of devices A and B, respectively.

Figure 3

(a) Nonlocal Hanle precession curves measured on device B at 4 K with a DC injection current of −130 μA. The red and black symbols are for signals measured when the injector and detector are in parallel and antiparallel configurations, respectively. The solid lines are fitting based on the 1-D spin-drift diffusion model, from which the spin lifetime is extracted to be 1.08 ns. (b) Temperature-dependent spin lifetimes measured on device A (solid circles) and B (open squares), respectively.

Figure 4

(a) The DC bias-dependent Δ$R_{\mathrm{NL}}$ of device A at different temperatures. The inset shows the restored DC relation between the $V_{\mathrm{NL}}$ and $I_{\mathrm{DC}}$ at 10 K by numerically integrating our $V_{\mathrm{NL}}$ over $I_{\mathrm{DC}}$. (b) and (c) Hanle precession curves measured on device A at 10 K under a reverse bias of −20 μA and a forward bias of +20 μA, respectively. The spin lifetimes extracted from the fittings (solid lines) based on the 1-D spin drift diffusion model are 773 ps and 332 ps for reverse and forward biases, respectively. The insets show the locations of the spin accumulation.