Single phosphorus ion implantation into prefabricated nanometre cells of silicon devices for quantum bit fabrication

In the near future, devices that employ single atoms to store or manipulate information will be constructed. For example, a solid-state quantum computer has been proposed that encodes information in the nuclear spin of shallow arrays of single P-31 atoms (quantum bits or qubits) in a matrix of pure silicon. Construction of these devices presents formidable challenges. One strategy is to use single ion implantation, with the energy range of 10 to 20 keV, to load the qubits into prefabricated cells of the device with a period of a few tens of nanometres. We have developed a method of single ion implantation that employs detector electrodes adjacent to the prefabricated qubit cells that can detect on-line single keV ion strikes appropriate for the fabrication of shallow arrays. Our method of the sub-20keV single ion detection utilizes a pure silicon substrate with a very high resistivity, a thin (5 nm) SiO2 surface layer, biased electrodes applied to the surface and sensitive electronics that can detect the charge transient from single keV ion strikes. We show that our detectors have a near 100% efficiency for keV ions, extremely thin dead layer thickness (similar to5 nm) and a wide sensitive region extending laterally from the electrodes (greater than 15 mum) where the nanometre cells can be constructed. We compare the method with the other methods, such as those of measuring the secondary electrons or phonons induced by single ion impacts.