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Germanium and silicon-germanium alloys have found entry into Si technology thanks to their compatibility with Si processing and their ability to tailor electronic properties by strain and band-gap engineering. Noticeably, the quasi-direct band structure of Ge allows for optical spin orientation bridging the fields of spintronics and Si photonics where Ge is increasingly applied [3,4]. Despite recent progress in the investigation of spin dynamics in Ge, very little is known about spin flip scattering by dopants and the role played by impurities in determining spin properties in different temperature regimes. Here we present a combined experimental and theoretical investigation of the spin and energy relaxation of electrons in Ge. By taking advantage of polarization-resolved photoluminescence measurements and Monte Carlo simulations of carrier dynamics we unveil unique and very rich spin physics and highlight the importance of the multi-valley conduction band of this material. We demonstrate full control over the angular momentum of the direct gap emission with a complete reversal between right- and left-handed circular polarization. This detailed investigation of spin properties of Ge is expected to open new opportunities connected to photonics and spintronics on mainstream CMOS-compatible platforms.

Ge is emerging as an interesting material for spintronic applications. We demonstrate that in SiGe heterostructures strain and quantum confinement effects can be used to tailor spin related properties enhancing the spin polarization of injected carriers above the bulk limit. Moreover the fast ?-L electron scattering and the strain induced removal of the heavy-hole, light-hole degeneracy, make SiGe heterostructures an ideal material platform for the study of hole dynamics. © The Electrochemical Society

Numéro de référence interne originel : a1.2 g 276

We performed spin-resolved photoluminescence measurements on Ge/SiGe multiple quantum wells with different well thickness and using different exciting power densities. The polarization of the direct emission strongly depends on the relative weight of electrons photoexcited from the light and the heavy hole subbands. The study of the polarization as a function of the exciting power highlights the role of the carrier-carrier interactions in determining spin depolarization. © 2013 AIP Publishing LLC.

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We demonstrate optical orientation in Ge/SiGe quantum wells and study their spin properties. The ultrafast electron transfer from the center of the Brillouin zone to its edge allows us to achieve high spin-polarization efficiencies and to resolve the spin dynamics of holes and electrons. The circular polarization degree of the direct-gap photoluminescence exceeds the theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and light holes states, respectively. The spin lifetime of holes at the top of the valence band is found to be ~0.5 ps and it is governed by transitions between heavy and light hole states. Electrons at the bottom of the conduction band, on the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical analysis of the electrons spin relaxation indicates that phonon-induced intervalley scattering dictates the spin lifetime., 5 pages, 3 figures