Atomic-layer doping of SiGe heterostructures for atomic-precision donor devices

As a first step to porting scanning tunneling microscopy methods of atomic-precision fabrication to a strained-Si/SiGe platform, we demonstrate post-growth P atomic-layer doping of SiGe heterostructures. To preserve the substrate structure and elastic state, we use a T <= 800 degrees C process to prepare clean Si0.86Ge0.14 surfaces suitable for atomic-precision fabrication. P-saturated atomic-layer doping is incorporated and capped with epitaxial Si under a thermal budget compatible with atomic-precision fabrication. Hall measurements at T = 0.3 K show that the doped heterostructure has R-square = 570 +/- 30 Omega, yielding an electron density n(e) = 2.1 +/- 0.1 x 10(14) cm(-2) and mobility mu(e) = 52 +/- 3 cm(2) V-1 s(-1), similar to saturated atomic-layer doping in pure Si and Ge. The magnitude of mu(e) and the complete absence of Shubnikov-de Haas oscillations in magnetotransport measurements indicate that electrons are overwhelmingly localized in the donor layer, and not within a nearby buried Si well. This conclusion is supported by self-consistent Schrodinger-Poisson calculations that predict electron occupation primarily in the donor layer.