Ab initio calculation of energy levels for phosphorus donors in silicon

Why Te Doping Can Break the Traditional n-Type Doping Limit of Silicon

We report a theoretical investigation of the impact of hyperdoping with chalcogens (Se and Te) and pnictogens (P and As) on free-carrier concentrations of Si, employing density functional theory calculations. Our results illustrate that isolated substitutional chalcogens in moderately doped Si function as deep donors that are difficult to ionize at room temperature, unlike isolated substitutional pnictogens. The pairing of substitutional defects is found to be energetically favorable for every dopant element, implying that the concentration of substitutional pairs can be significant in hyperdoped Si. However, chalcogen-substitutional pairs have the capability to increase the carrier concentration, whereas pnictogen-substitutional pairs serve only as compensators for n-type doping. By evaluating the carrier concentrations for Te- and P-hyperdoped Si, we demonstrate the importance of substitutional Te pairs of Te-hyperdoped Si in breaking the traditional n-type doping limit observed in pnictogen-hyperdoped Si. Our work elucidates the underlying microscopic mechanisms that give rise to substantial carrier densities in chalcogen-hyperdoped Si, which will pave the way for the development of high-performance silicon-based devices.

GeVn complexes for silicon-based room-temperature single-atom nanoelectronics

We propose germanium-vacancy complexes (GeV_n) as a viable ingredient to exploit single-atom quantum effects in silicon devices at room temperature. Our predictions, motivated by the high controllability of the location of the defect via accurate single-atom implantation techniques, are based on ab-initio Density Functional Theory calculations within a parameterfree screened-dependent hybrid functional scheme, suitable to provide reliable bandstructure energies and defect-state wavefunctions. The resulting defect-related excited states, at variance with those arising from conventional dopants such as phosphorous, turn out to be deep enough to ensure device operation up to room temperature and exhibit a far more localized wavefunction.

Towards visualisation of central-cell-effects in scanning tunnelling microscope images of subsurface dopant qubits in silicon

Atomic-scale understanding of phosphorus donor wave functions underpins the design and optimisation of silicon based quantum devices. The accuracy of large-scale theoretical methods to compute donor wave functions is dependent on descriptions of central-cell corrections, which are empirically fitted to match experimental binding energies, or other quantities associated with the global properties of the wave function. Direct approaches to understanding such effects in donor wave functions are of great interest. Here, we apply a comprehensive atomistic theoretical framework to compute scanning tunnelling microscopy (STM) images of subsurface donor wave functions with two central-cell correction formalisms previously employed in the literature. The comparison between central-cell models based on real-space image features and the Fourier transform profiles indicates that the central-cell effects are visible in the simulated STM images up to ten monolayers below the silicon surface. Our study motivates a future experimental investigation of the central-cell effects via the STM imaging technique with potential of fine tuning theoretical models, which could play a vital role in the design of donor-based quantum systems in scalable quantum computer architectures.