Tuning spin-orbit coupling in silicon and germanium for spin generation, detection and manipulation

Published : 13 December 2016

The aim of semiconductor spintronics is to use the electron spin in addition to its charge in microelectronics devices. The spin degree of freedom adds new functionalities to existing devices and will allow to reduce power consumption. The three requirements for the development of such technology are the generation, detection and manipulation of spin polarized electrons in Si or Ge (the materials of today’s microelectronics). A new paradigm has recently raised in the spintronics community which consists in using the spin-orbit coupling to complete those three operations. The spin-orbit coupling couples the electron momentum and spin. Hence, it makes possible the spin manipulation by electric fields but also the inter-conversion between charge currents and spin currents by the spin Hall effect in bulk materials or the Rashba effect at interfaces.

Unfortunately, in bulk Si and Ge, the spin-orbit coupling is too weak and this is the objective of this thesis work to study ways to enhance it. First, we will focus on metal/Si(111) and Ge(111) interfaces where the Rashba spin-orbit coupling is predicted very strong. Then, two more promising systems will be investigated: topological insulator/Si(111) and Ge(111) interfaces as well as Si and Ge thin films doped with heavy atoms. The candidate will benefit from the long standing experience of our group in semiconductor spintronics and from the close collaboration with the CEA LETI.

In order to build the final spin transistor device, the student will perform the following tasks:

1) Epitaxial growth of magnetic tunnel junctions on Si, Ge. They will constitute the spin injection and detection électrodes.

2) Epitaxial growth of the metal/Si and metal/Ge Rashba states

3) Nanofabrication of the devices in the clean room using optical and electronic lithography

4) Magnetotransport measurements on the final devices using a dedicated cryostat (2-300 K, 0-7 Tesla)

5) Interpretation of electrical signals using existing models. Development of new models. Finite elements numerical simulations to visualize the spin currents in the structures.

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