Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer

The incorporation of phosphorus in silicon is studied by analyzing phosphorus δ-doped layers using a combination of scanning tunneling microscopy, secondary ion mass spectrometry, and Hall effect measurements. The samples are prepared by phosphine saturation dosing of a Si(100) surface at room temperature, a critical annealing step to incorporate phosphorus atoms, and subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation $\text{(∼5\hspace{0.17em}}\mathrm{nm}\mathrm{),}$ complete electrical activation at a silicon growth temperature of $\text{250\hspace{0.05em}°}\mathrm{C}$ and a high two-dimensional electron mobility of ${\text{∼10}}^2\hspace{0.17em}{\mathrm{cm}}^2/\mathrm{V s}$ at a temperature of 4.2 K. These results, along with preliminary studies aimed at further minimizing dopant diffusion, bode well for the fabrication of atomically precise dopant arrays in silicon such as those found in recent solid-state quantum computer architectures.