Reduction of carrier density and enhancement of the bulk Rashba spin-orbit coupling strength in Bi2Te3/GeTe superlattices

Abstract

Featured with the large Rashba constant (alpha R -4.2 eV angstrom) coupled with the ferroelectricity, GeTe has attracted much interest, proposing novel energy-efficient spintronic devices. However, those approaches are ham-pered by the high hole density of GeTe around 1020-1021 cm-3, which deteriorates both the ferroelectricity and the bulk Rashba effect of GeTe. To solve this problem, we have investigated the superlattices composed of Bi2Te3 and GeTe ([BT|GT] SL), the former of which is known as a topological insulator (TI) with typically n- type conduction and strong spin-orbit coupling. We have investigated the magnetotransport properties of 25 [BTx|GTy]z SLs with varying thicknesses (x, y: the thickness in the multiples of the unit cell of the re-spective layer) of each layer and the repetition number (z) systematically. We have observed a minimum carrier density of 5.7 x 1019 cm-3 in [BT6|GeTe6]6 superlattice sample smaller than that (-4.4 x1020 cm-3) of GeTe single film by an order. In addition, we have found that some [BT|GT] SLs with reduced carrier density have a larger Rashba constant compared to that of a single GeTe film. This is explained by the change of the spin polarization which can be modulated by the Fermi level in the Rashba band. These results provide a viable way to realize robust ferroelectricity and strong SOC in GeTe-related material systems simulta-neously.(c) 2023 Elsevier B.V. All rights reserved.