Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3

Abstract

A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As a first approach, devices were fabricated consisting of thin (<100nm) exfoliated crystals of Bi 2 Se 3 on n-type silicon with independent electrical contacts to silicon and Bi 2 Se 3 . Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi 2 Se 3 interface. This robust Schottky barrier opens the possibility of novel device designs based on sub-band gap internal photoemission from Bi 2 Se 3 into Si.The most remarkable feature of the three-dimensional strong topological insulators (TIs) is the existence of a metallic surface state within the bulk bandgap with chiral charge carriers exhibiting perfect spin-momentum coupling. The chiral TI surface state has been proposed as the basis of spintronics and quantum computing devices. 1,2 Although the spin helicity of the TI surface has been experimentally measured by spin-angle resolved photoemission spectroscopy (spin-ARPES) 3-5 , no electrical transport experiment has yet shown clear evidence of it for several reasons. Since spin and momentum are perfectly coupled, non local measurement of a spin current in the absence of a charge current 6,7 is precluded. Perhaps even more importantly, spin precession induced by a weak perpendicular magnetic field is also eliminated by momentum scattering in the diffusive regime. This is particularly problematic since evidence of spin precession and dephasing are used to unambiguously identify spin transport in both inorganic semiconductors 8 and metals 9 .Direct measurement of the spin Hall effect by injection of spin from a ferromagnetic (FM) contact is also problematic since the desired signal will be difficult to distinguish from the ordinary Hall effect due to stray fields from the nearby FM electrode.More sophisticated measurement geometries are unlikely to solve the problem. For instance, if the FM magnetization is oriented by an in-plane magnetic field at an angle with the charge current, anisotropic magnetoresistance results. This gives rise to a planar Hall effect 10-12 which is difficult to distinguish from a signal due to the spin-momentum coupling in the TI 13 . The situation would not be different if the current flows perpendicular to the interface between TI and the ferromagnet, since the strong spin orbit interaction of the TI may induce an anisotropic tunneling magnetoresistance signal, as has been observed in devices consisting of a tunneling barrier between a ferromagnet and a non-magnetic layer. 14,15 Here, we propose a class of transport experiments a) Condensed Matter and Materials division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA (present address) to confirm the spin-momentum coupling in TI surface states which circumvents these problems by injecting spin polarized electrons from a long-distance silicon transport channel into the topological ...

Topological Insulator Materials

“…This is because the spin-momentum locking makes the charge and spin scattering times to be the same, and therefore the spin diffusion length is equal to the electron mean free path in the TI surface state. 219) In such a situation, the spin polarization is significantly diminished in a diffusive transport (to the order of Ák=k F , where Ák is the shift of the Fermi surface induced by the applied electric field), 220) and the experiment must be done in a ballistic transport regime to detect a spinpolarized current. 221) No such experiment has been reported for 3D TIs, but in the CdTe/HgTe/CdTe quantum well in the 2D TI regime, spin polarization of the edge current has been confirmed, 70) thanks to the long electron mean free path achievable in HgTe quantum wells.…”

Ultrabroadband, Large Sensitivity Position Sensitivity Detector Based on a Bi2Te2.7Se0.3/Si Heterojunction and Its Performance Improvement by Pyro‐Phototronic Effect

“…Besides, Bi 2 Te 3 and Bi 2 Se 3 are all stoichiometric rhombohedral materials with quintuple stacked layered structure and relatively weak layer-tolayer van der Waals coupling, [19] as shown in Figure 1a. More importantly, it was suggested that the construction of Bi 2 Se 3 on Si could introduce a very high Schottky barrier of ≈0.34 eV at the interface, [22,28,29] which can be used to accelerate the separation of photo-excited carriers in Si or Bi 2 Se 3 and inhibit their recombination simultaneously, thus the outstanding photoelectric responses were usually obtained. More importantly, it was suggested that the construction of Bi 2 Se 3 on Si could introduce a very high Schottky barrier of ≈0.34 eV at the interface, [22,28,29] which can be used to accelerate the separation of photo-excited carriers in Si or Bi 2 Se 3 and inhibit their recombination simultaneously, thus the outstanding photoelectric responses were usually obtained.…”

Newtype large Rashba splitting in quantum well states induced by spin chirality in metal/topological insulator heterostructures

“…51 We have used the condition V≫E in the above approximation, which is reasonable for the Ag/Bi 2 Se 3 junctions. As the TI SOC causes the Rashba-type splitting by affecting the tunneling part of the metallic QWS, the spin gap ΔE defined in Figure 2a should be proportional to the tunneling amplitude in TI:…”