STRAIN ENGINEERING OF SILICON FOR SPINTRONICS APPLICATIONS

Work package:
Despite decades of research in spintronics, demonstration of all-optical detection and control of electron spins in silicon - still the most important and ubiquitous semiconductor in today's microelectronics industry - remains elusive. Many prototype devices for processing and transmitting quantum information are based today on this strategic material. It is also in silicon that Georges Lampel's pioneering experiments were carried out in 1968 on optical spin orientation in solids 1 , wherein it was shown that polarized electronic spins are produced by optical pumping with circularly polarized light, yielding a dynamic polarization of Si29 nuclei. The Lampel’ studies have triggered very active research on the use of polarized light to study and control the spin of electrons in various III-V, II-VI, and group-IV semiconductors (eg, GaAs, CdTe, and Ge) and more recently in 2D semiconductors such as MoS 2 . The optical techniques (luminescence, absorption, reflectivity) coupled with theoretical studies have made it possible to discover the optical selection rules and the spin relaxation mechanisms in a large variety of semiconductor structures 2 . Surprisingly these great advances did not concern free electrons in bulk silicon for which precise optical studies are more challenging since it is an indirect-gap semiconductor with weak phonon-assisted optical emission in the near infrared. Recently we measured for the first time circularly polarized silicon luminescence after optical spin orientation under both direct and indirect gap excitation conditions3 . These experiments lead to (i) the determination of the optical selection rules for the different transitions assisted by phonon emission (TO, LO and TA) and (ii) the measurement of the spin relaxation time of free electrons. The objective of this internship is to apply strain to silicon in order to suppress electron spin relaxation. This predicted4 but never measured effect could lead to concrete applications based on the optical control of the electron spin degree of freedom with the most widely used material in microelectronics. The main part of the work will consist in (i) designing experimental systems to apply biaxial compression or uniaxial tension along a given crystallographic axis and (ii) measuring the strain amplitude by Raman spectroscopy. If the results are conclusive, polarized photoluminescence experiments at low temperature will be implemented in order to measure the electron spin properties.