Epitaxial growth of insulator oxides on semiconductors is a key topic in electronics and spintronics, and Ge, due to its high electronic and hole mobilities, represents a promising candidate for the next generation high performance Complementary Metal-Oxide-Semiconductor Field-Effect Transistor (CMOSFET). Moreover, Germanium is expected to play a relevant role in Spintronics, due to the large spin-orbit splitting allowing spin manipulation via external fields, thus envisaging the development of “spin-devices” (such as spin-transistors and spin-valves) where the charge is substituted by the spin as information carrier.
Our research in this field is focused on Fe/MgO/Ge(001) heterostructures, grown by Molecular Beam Epitaxy [1,2] and magnetron sputtering and characterized in-situ by electron spectroscopies and diffraction techniques. The spin transport properties are measured by optical and magneto-transport techniques on protoypical devices fabricated by (optical and electron-beam lithography), such as spin-photodiodes and lateral transport devices.
In this frame, we recently realized and reported in Advanced Materials [4] the first demonstration of room-temperature operation of Ge-based spin-photodiodes for integrated electrical detection of the light polarization, finally opening the way towards a Ge-based spin-opto-electronics on a wide spectral range [5].
A second research line on semiconductor spintronics focuses on the narrow gap ferroelectric semiconductor GeTe, for which the opportunity for the electric control of the Giant Rashba Effect has been predicted. In-situ and synchrotron-based (Elettra) characterization of GeTe thin films are in progress, in order to evaluate the opportunity of realizing a spin-transistor with GeTe employed as gate and active channel.
References
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- Cantoni, D. Petti, C. Rinaldi, and R. Bertacco, “Bandstructure line-up of epitaxial Fe/MgO/Ge heterostructures: A combined x-ray photoemission spectroscopy and transport study”, Appl. Phys. Lett. 98, 032104 (2011)
- Petti, M. Cantoni, C. Rinaldi, S. Brivio, R. Bertacco, J. Gazquez, and M. Varela, “Sharp Fe/MgO/Ge(001) epitaxial heterostructures for tunneling junctions”, J. Appl. Phys. 109, 084909 (2011)
- Rinaldi, M. Cantoni, D. Petti, and R. Bertacco, “Epitaxial Fe/MgO/Ge spin-photodiodes for integrated detection of light helicity at room temperature”, J. Appl. Phys. 111, 07C312 (2012)
- Rinaldi, M. Cantoni, D. Petti, A. Sottocorno, M. Leone, N. M. Caffrey, S. Sanvito and R. Bertacco, “Ge-based spin-photodiodes for room temperature integrated detection of photons helicity”, Adv. Mat. 24, 3037 (2012), DOI: 10.1002/adma.201104256
- Rinaldi, M. Cantoni, M. Marangoni, C. Manzoni, G. Cerullo, R. Bertacco, “Wide range optical spin orientation in Ge: from near infrared to visible”, Phys. Rev. B 90, 161304(R) (2014), DOI: 10.1103/PhysRevB.90.161304
- M. Cantoni and C. Rinaldi, “Light helicity detection in MOS-based spin-photodiodes: an analytical model”, J. Appl. Phys. 120, 104505 (2016), doi: 10.1063/1.4962204
- C. Rinaldi, S. Bertoli, M. Asa, L. Baldrati, C. Manzoni, M. Marangoni, G. Cerullo, M. Bianchi, R. Sordan, R. Bertacco and M. Cantoni, “Determination of the spin diffusion length in germanium by spin optical orientation and electrical spin injection”, J. Phys. D: Applied Physics 49, 425104 (2016), doi: 10.1088/0022-3727/49/42/425104