Recent studies revealed that spin diffusion length (λs) and spin lifetime (τs) of electrons in Ge are governed by spin-flip scattering among conduction band valleys (intervalley spin-flip scattering) 1. To reduce the intervalley spin-flip scattering frequency, Tang et al. have theoretically predicted that lifting the degenerate four valleys through a lattice strain is effective 2. In this study, we experimentally study the effect of strain on spin transport in strained Si0.1Ge0.9, which exhibits a Ge-like electronic band structure.
A strained n-Si0.1Ge0.9 spin transport layer (~70 nm) with a carrier concentration (n) of ~1×1018 cm-3 was grown on Ge/Si(111) substrates by molecular beam epitaxy (MBE), where the in-plane tensile strain of ~0.66% was confirmed by reciprocal space map. Then, we fabricated lateral spin-valve (LSV) devices with a Co-based Heusler alloy spin injector/detector 3,4. A representative four-terminal nonlocal spin signal (|ΔRNL|) at room temperature is shown in the inset of Fig. 1. Figure 1 shows contact distance (d)-dependent |ΔRNL| at room temperature for LSV devices with the strained n-Si0.1Ge0.9 and an n-Ge. The dashed lines are fits to the data using |ΔRNL| ∝ exp(-d/λs) and the estimated value of λs for the strained n-Si0.1Ge0.9 (n-Ge) is estimated to be ~0.93 µm (~0.50 µm). Notably, an approximately twofold increase in λs is attributed to the enhanced electron mobility and spin lifetime, induced by lifting the valley degeneracy and by obtaining relatively low carrier concentration 5. We also demonstrate long-distance spin-drift transport under the electric field (E) and clearly observe pronounced Hanle oscillations with d = 7 µm at T = 50 K in a three-terminal measurement with a drift current of ID = -0.5 mA, as shown in Fig. 2.
1 K. Hamaya et al., J. Phys. D: Appl. Phys., Vol. 51, p.393001 (2018) 2 J. -M. Tang et al., Phys. Rev. B, Vol. 85, p.045202 (2012) 3 M. Yamada et al., NPG Asia Mater., Vol. 12, p.47 (2020) 4 K. Kudo et al., Appl. Phys. Lett., Vol. 118, p.162404 (2021) 5 T. Naito et al., Phys. Rev. Applied (accepted)