Abstract
Topological insulators (TIs) like Bi2Se3 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 Bi2Se3 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 Bi2Se3 on germanium, we aim at combining the long spin diffusion length of Ge with the spin-momentum locking at the surface of Bi2Se3. We first performed a thorough structural analysis of Bi2Se3 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 presence of spin-orbit coupling. We interpret our results as the signature of magnetotransport in a single strongly coupled coherent channel in the presence of surface to bulk scattering. Interestingly, the magnetotransport measurements also point out that the conduction channel can be tuned between the Bi2Se3 film and the Ge layer underneath by means of the bias voltage or the applied magnetic field. This result suggests that the Bi2Se3/Ge junction is a promising candidate for tuning spin-related phenomena at interfaces between TIs and semiconductors.
Highlights
In the past decade, topological insulators (TI) have gained much interest in the field of spintronics for the generation and detection of spin currents
Since the film is n-doped by growth-induced selenium vacancies, we demonstrate the existence of a pn junction that can exhibit two transport regimes depending on the bias voltage and magnetic field applied to the junction
Ultrathin films of Bi2Se3 were grown on Ge(111) by molecular beam epitaxy (MBE), the surface quality and structure were followed by reflection high-energy electron diffraction (RHEED) all along the growth
Summary
The interface with a long spin diffusion length (lsf ) material that can be optically active like germanium.[17,18] In this study, we report the epitaxial growth of a Bi2Se3 thin film by MBE on lowdoped Ge(111) (p ≈ 1015 cm−3). Since the film is n-doped by growth-induced selenium vacancies, we demonstrate the existence of a pn junction that can exhibit two transport regimes depending on the bias voltage and magnetic field applied to the junction. By adjusting both parameters, it is possible to select the Bi2Se3 channel with spin-momentum locking at surface states or the Ge channel with long spin diffusion length
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