Ge-vacancy complexes: a viable route toward quantum information processes at room temperature

*Simona Achilli (1), Nicola Manini (2), Guido Fratesi (2), Giovanni Onida (2), Takahiro Shinada (3), Takashi Tanii (4) and Enrico Prati (5)
(1) Catalan Institute of Nanoscience and Nanotecnology, Spain. (2) Department of Physics, University of Milan, Italy. (3) Center for Innovative Integrated Electronic Systems, Tohoku University, Japan. (4) Faculty of Science and Engineering, Waseda University, Japan. (5) Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche, Italy.

The development of on-demand individual deep impurities in silicon is motivated by their employment as a physical substrate for qubits [1], nanoscale transistors [2], single photon emitters [3] and Hubbard simulators [4]. Single-atom silicon devices based on conventional doping elements such as phosphorous [5-7] can operate only at cryogenic temperature due to shallow weakly localized ground state impurity levels.

Differently, the implantation of Ge dopants in silicon and the subsequent annealing generate stable Ge-vacancy defects [8] that are promising candidates to achieve single-atom quantum effects at room temperature. These hybrid complexes combine indeed the properties of the silicon vacancy, which carries deep states in the band-gap, with the accurate spatial controllability of the defect obtainable through state of the art single-ion implantation of Ge atom.

We characterize GeVn complexes in silicon by means of accurate ab initio density functional theory calculations with a hybrid functional. We get insight on the defect local arrangement and on their electronic properties, demonstrating their suitability for the purposed application. We show that due to the deep defect levels the electrons bound to the defects are strongly correlated and more localized than in conventional dopants [9]. Through a multi-scale theoretical approach that combines ab initio DFT and an extended Hubbard model we analyze also the electronic transport through a chain of GeV dopants. By mapping the ab initio results into the model Hamiltonian we are able to describe the electronic conductance of the array as a function of the temperature and to determine the activation energy for hopping processes.

We compare the theoretical results with the experimental data showing a notable agreement between the calculated and measured excited state energies and temperature activated transport properties [10].

This work has been performed in the context of a user access request within the Nanoscale Facilities and Fine Analysis project [11], funded by European Community.

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[5] E. Prati, et al., Nature Nanotech. 7, 443 (2012).

[6] E. Prati, et al., Sci. Rep. 6, 19704 (2016).

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[9] S. Achilli et al., Sci. Rep. 8, 18054 (2018).

[10] S. Achilli et al. (unpublished, in preparation)

[11] https://nffa.eu