The SemiSpin laboratory constitutes a new research branch of the Surface Physics group, entirely devoted to spintronics in group-IV heterostructures and metal/semiconductors systems. Spin generation, transport and dynamics lie at the cutting edge of solid-state physics and semiconductors are prototypical systems to study spin-related phenomena due to their large spin-orbit coupling and long electron spin lifetime. In particular, experimental activities are focussed on Ge-based spintronics, such as bulk and compressively-strained germanium, Ge/SiGe multiple quantum wells, bulk and compressively-strained SiGe alloys. Moreover, part of the experimental activity is also devoted to the study of spin currents in III-V semiconductor heterostructures. These studies are performed by applying electric bias, magnetic fields and changing the doping level of the semiconductor layer.

Spin generation is studied by means of spin-polarized photoemission. The laboratory is equipped with a 20 kV-Mott polarimeter (see Fig. 1a), that allows the detection of the spin polarized electron beams. The spin orientation is obtained by exciting the electrons in the conduction band of the semiconductor through circularly polarized light, a process known as optical orientation. The engineering of the semiconductor band structure, through strain and quantum confinement, results in a very high electron spin polarization, as shown in Fig. 1.

Spin transport and dynamics are also studied by measuring spin currents in metal/semiconductor devices. In this case, the semiconductor is used as spin current generator, whereas the metal (usually Pt) is used as spin current detector. A pure spin current Js is optically generated in the semiconductor (the direction of the spin vector σ is out of plane in Fig. 2a). It then flows towards the Pt layer where it is converted into an electromotive force VISHE through spin-orbit scattering with Pt-nuclei, a process called Inverse Spin Hall Effect (ISHE). The optical generation of spin currents is provided by a Ti: sapphire tunable laser in the range 1.1 - 1.8 eV. As an example, Fig. 2b shows the spin current in a Pt/Ge(001) sample, as a function of the incident photon energy.

Selected publications:

1. F. Bottegoni, G. Isella, S. Cecchi, and F. Ciccacci, Appl. Phys. Lett. 98, 242107 (2011).
2. F. Bottegoni, A. Ferrari, G. Isella, S. Cecchi, M. Marcon, D. Chrastina, G. Trezzi, and F. Ciccacci, J. Appl. Phys. 111, 063916, (2012).
3. F. Pezzoli, F. Bottegoni, D. Trivedi, F. Ciccacci, A. Giorgioni, P. Li, S. Cecchi, E. Grilli, Y. Song, M. Guzzi, H. Dery, and G. Isella, Phys. Rev. Lett. 108, 156603 (2012).
4. F. Bottegoni, A. Ferrari, G. Isella, M. Finazzi, and F. Ciccacci, Phys. Rev. B 85, 245312 (2012).
5. A. Ferrari, F. Bottegoni, S. Cecchi, G. Isella, and F. Ciccacci, J. Appl. Phys. 113, 17C504 (2013).
6. F. Bottegoni, A. Ferrari, S. Cecchi, M. Finazzi, F. Ciccacci, and G. Isella, Appl. Phys. Lett. 102, 152411 (2013).