Correlation between spin transport signal and Heusler/semiconductor interface quality in lateral spin-valve devices

Abstract

We show a direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on the spin transport signals in semiconductor-based lateral spin-valve (LSV) devices. Based on atomic scale Z contrast scanning transmission electron microscopy and energy dispersive x-ray spectroscopy we show that atomic order/disorder of Co2FeAl0.5Si0.5 (CFAS)/n-Ge LSV devices is critical for the spin injection in Ge. By conducting a post annealing of the LSV devices, we find 90% decrease in the spin signal while there is no difference in the electrical properties of the CFAS/n-Ge contacts and in the spin diffusion length of the n-Ge layer. We show that the reduction in the spin signals after annealing is attributed to the presence of intermixing phases at the Heusler/semiconductor interface. First principles calculations show how that intermixed interface region has drastically reduced spin polarisation at the Fermi level, which is the main cause for the significant decrease of the spin signal in the annealed devices above 300 • C.

Spin injection through energy-band symmetry matching with high spin polarization in atomically controlled ferromagnet/ferromagnet/semiconductor structures

“…The detailed fabrication procedure of the LSV devices is described in the Materials and methods. Additionally, similar LSV structures were presented in our previous works [15][16][17]20,21 . We note that the highly spin-polarized material CFAS is utilized as a spin injector and detector for Ge, where CFAS is one of the ferromagnetic Heusler alloys 15,16,22 .…”

“…1b are reproduced for many LSV devices. The value of RA for the spin injection and detection electrodes was maintained at less than 0.40 kΩ µm 2 after Fe atomic layer insertion because the electrical characteristics of the electrodes were controlled by the phosphorus δ-doped layer near the CFAS/Ge interface 16,20 . The detailed J-V characteristics are presented in Supplementary Fig.…”

Simultaneous Prediction of the Magnetic and Crystal Structure of Materials Using a Genetic Algorithm

“…For the CFAS/semiconductor interface, germanium provides an extremely good lattice match with only a 0.2% mismatch, compared to around 4.5% for CFAS/Si. However, when CFAS is grown on n-type germanium, significant mixing at the interface can occur, as evidenced by energy dispersive X-ray spectroscopy (EDS) [36] (see Figure 8). In addition, annealing the sample at 575 K forms a plateau in the cobalt intensities and, to a lesser extent, the iron and germanium intensities, as seen in the EDS results in Figure 9.…”

“…Energy dispersive X-ray spectroscopy (EDS) results across the as-grown CFAS/n-Ge interface, showing significant mixing of the atomic species. Data taken from Kuerbanjian et al[36].…”

“…Plateaux can be seen around 6.5-8.6 nm in Co, Fe and Ge, indicated by the shaded region. Data taken from Kuerbanjian et al[36].…”