Influence of doping density on electronic transport in degenerate Si:Pδ-doped layers

We present a detailed study addressing the effect of doping density on electronic transport in Si:P $\delta$-doped layers grown by phosphine dosing and low temperature molecular beam epitaxy. We demonstrate that the surface P coverage can be determined directly from scanning tunneling microscope analysis of $\mathrm{P}{\mathrm{H}}_3$ dosed Si(100) surfaces, with good quantitative agreement to that measured by Auger electron spectroscopy. For samples with doping densities between $\sim 1\times {10}^{13}{\mathrm{cm}}^{-2}\text{to}\sim 5\times {10}^{14}{\mathrm{cm}}^{-2}$, we found that mobility decreases with higher doping. In contrast, both the mean free path and phase coherence length increase with doping density up to a maximum at a room-temperature saturation dose of phosphine $(\sim 2\times {10}^{14}{\mathrm{cm}}^{-2})$. We discuss the implications of our results for the fabrication of nanoscale Si:P devices by scanning probe lithography and phosphine dosing.