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

TL;DR

This study demonstrates the epitaxial growth of Bi$_2$Se$_3$ topological insulator films on germanium, revealing tunable surface state conduction and potential for spintronic applications through interface engineering.

Contribution

First successful epitaxial growth of Bi$_2$Se$_3$ on Ge(111) and analysis of its tunable magnetotransport properties highlighting interface control.

Findings

Observation of weak antilocalization indicating 2D surface state transport

Conduction channel can be tuned via bias voltage or magnetic field

Bi$_2$Se$_3$/Ge interface shows promise for spintronic devices

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.