Ge-Vn complexes in silicon: a viable route toward room temperature single atom devices*

Single-atom transistors are the ultimate scaling solution for applications in quantum information. Devices based on conventional dopant atoms (As, P) in silicon can operate only at cryogenic temperature due to shallow
weakly localized impurity levels. Ge dopants are promising candidates for operating single-electrons at room temperature, forming stable defect complexes with single or multiple vacancies, characterized by very deep levels in the energy gap.
By means of ab initio Density Functional Theory (DFT) calculation with screened-exchange hybrid functional, that solves the “gap and delocalization problem” of standard DFT, we characterize structural and electronic properties of different Ge-Vn defects. We compute the adiabatic and thermodynamic charge transition levels corresponding to the excitation energies for the addition of electrons to the defect. We show that the energy position of these excited states in the gap and their localization on the defects may shed light on the physics behind the features observed in the experimental I-V curves and on the electron transport mechanisms in the system.