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 δ-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 PH₃ dosed Si(100) surfaces, with good quantitative agreement to that measured by Auger electron spectroscopy. For samples with doping densities between ${~}1×{}{10}¹³{{0.3em}{0ex}}{cm}^{{-}2}{{0.3em}{0ex}}to{{0.3em}{0ex}}{~}5×{}{10}¹⁴{{0.3em}{0ex}}{cm}^{{-}2}$, 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 (~2×10¹⁴0.3em0excm^-2). We discuss the implications of our results for the fabrication of nanoscale Si:P devices by scanning probe lithography and phosphine dosing.