Magnetotransport in Bi${}_2$Se${}_3$ thin films epitaxially grown on Ge(111)

Abstract

Topological insulators (TIs) like Bi${}_2$Se${}_3$ are a class of material with topologically protected surface states in which spin-momentum locking may enable spin-polarized and defect-tolerant transport. In this work, we achieved the epitaxial growth of Bi${}_2$Se${}_3$ thin films on germanium, which is a key material for microelectronics. Germanium also exhibits interesting properties with respect to the electron spin such as a spin diffusion length of several micrometers at room temperature. By growing Bi${}_2$Se${}_3$ on germanium, we aim at combining the long spin diffusion length of Ge with the spin-momentum locking at the surface of Bi${}_2$Se${}_3$. We first performed a thorough structural analysis of Bi${}_2$Se${}_3$ films using electron and x-ray diffraction as well as atomic force microscopy. Then, magnetotransport measurements at low temperature showed the signature of weak antilocalization as a result of two-dimensional transport in the topologically protected surface states of Bi${}_2$Se${}_3$. Interestingly, the magnetotransport measurements also point out that the conduction channel can be tuned between the Bi${}_2$Se${}_3$ film and the Ge layer underneath by means of the bias voltage or the applied magnetic field. This result suggests that the Bi${}_2$Se${}_3$/Ge junction is a promising candidate for tuning spin-related phenomena at interfaces between TIs and semiconductors.

18 pages, 8 figures