Critical issues in the formation of atomic arrays of phosphorus in silicon for the fabrication of a solid-state quantum computer

We present recent progress towards the fabrication of a silicon-based quantum computer, via a ‘bottom up’ strategy, which exploits a combination of scanning tunneling microscopy (STM) and molecular beam epitaxy. Following our recent success in the fabrication of an atomic array of P atoms in silicon we now address the critical issues leading to the encapsulation of this array in silicon. Exposing Si(0 0 1) to a low PH3 dose at room temperature results in the formation of a number of species on the surface. We use bias dependent STM to characterise these species and identify PHx (x=2,3) moieties and hemihydrides as the dominant surface adsorbates. We show that by controlled annealing we can incorporate single P atoms into the surface layer. We use STM lithography to depassivate regions of a H:Si(0 0 1) surface in order to confine the above adsorption/incorporation processes to nanometer sized areas.