Donors in Ge as qubits —Establishing physical attributes

Abstract

Quantum electronic devices at the single impurity level demand an understanding of the physical attributes of dopants at an unprecedented accuracy. Germanium-based technologies have been developed recently, creating a necessity to adapt the latest theoretical tools to the unique electronic structure of this material. We investigate basic properties of donors in Ge which are not known experimentally, but are indispensable for qubit implementations. Our approach provides a description of the wavefunction at multiscale, associating microscopic information from Density Functional Theory and envelope functions from state of the art multivalley effective mass calculations, including a central cell correction designed to reproduce the energetics of all group V donor species (P, As, Sb and Bi). With this formalism, we predict the binding energies of negatively ionized donors (D − state). Furthermore, we investigate the signatures of buried donors to be expected from Scanning Tunneling Microscopy (STM). The naive assumption that attributes of donor electrons in other semiconductors may be extrapolated to Ge is shown to fail, similar to earlier attempts to recreate in Si qubits designed for GaAs. Our results suggest that the mature techniques available for qubit realizations may be adapted to germanium to some extent, but the peculiarities of the Ge band structure will demand new ideas for fabrication and control.

An atomic scale study of Si-doped AlAs by cross-sectional scanning tunneling microscopy and density functional theory

“…The coupling among the 6 degenerate minima by the donor perturbation potential gives rise to interference patterns in the defect wavefunction 11 . These can be identified by STM [12][13][14][15][16] in the (001) surface as alternating patterns, on a 4-layer cycle, depending on the impurity depth from the surface 17 .…”

Atomic-scale study of Si-doped AlAs by cross-sectional scanning tunneling microscopy and density functional theory

“…The coupling among the six degenerate minima by the donor perturbation potential gives rise to interference patterns in the defect wave function [12]. These can be identified by STM [13][14][15][16][17] in the (001) surface as alternating patterns, on a four-layer cycle, depending on the impurity depth from the surface [18].…”