Single electrons trapped by individual donors in semiconductors are promising spin- qubit candidates due to their combined semiconductor and atomic characters , since recent studies have shown large spin relaxation times in bulk semiconductors . Moreover, they offer scalability, homogeneity and strong coupling to light.
In this seminar we present a study of the spin relaxation mechanisms for electrons localized on I-donors by Coulomb potential. The samples consist of a single 8-nm CdTe quantum well grown by molecular-beam epitaxy on a (100)-oriented GaAs substrate, with I-doping in the centre plane. The QW increases the localization of the electron wave function, with respect to its localization on donors in three-dimensional crystals, and is also known to purify the optical selection rules for the circularly-polarized transitions creating excitons bound to donors (D0X) .
We have determined the spin dephasing time as a function of the donor concentration  and the temperature. We used a degenerate pump-probe technique, the photo-induced Faraday rotation, which is well-adapted to study spin relaxation and decoherence times of both excited states and resident electrons. As in 3D materials , the maximum of the localized-spin coherence time as function of concentration is fixed by an interplay of two mechanisms in this 2D geometry:(i) the hyperfine interaction associate to exchange- interaction between a couple of electronic spins localized by donors ; (ii) the anisotropic exchange interaction related to the spin-orbit coupling. We have then determined the spin-orbit constant α = 0.079 for CdTe.
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