Ultradense phosphorous delta layers grown into silicon from PH3 molecular precursors

Phosphorous δ-doping layers were fabricated in silicon by ${\mathrm{PH}}_3$ deposition at room temperature, followed by low-temperature Si epitaxy. Scanning tunneling microscope images indicate large H coverage, and regions of $\text{c(2×2)}$ structure. Hall data imply full carrier activation with mobility $\text{<40\hspace{0.17em}}{\mathrm{cm}}^2/\mathrm{V s}$ when the surface coverage is $\text{≲0.2\hspace{0.17em}}\mathrm{ML}.$ Conductivity measurements show a $\ln \mathrm{(T)}$ behavior at low temperatures, characteristic of a high-density two-dimensional conductor. Possible future applications to atom-scale electronics and quantum computation are briefly discussed.