High Quality Two-Dimensional Electron Gases (2DEGs) in Isotopically-Enriched Strained Silicon

Silicon quantum dots (QDs) formed in a Si/SiGe two-dimensional electron gas (2DEG) are a promising candidate for quantum computation. To capture a single electron in a QD, the dot must be very small, which requires a short distance from the surface to Si 2DEG layer for fine gating. Here we demonstrate a high quality modulation-doped Si 2DEG grown by chemical vapor deposition (CVD), with a distance of 65 nm from the surface to 2DEG layer. The electron mobility at 0.3K of 504,000 cm$^{2}$/V-s (density 4.3 x 10$^{11}$ cm$^{-2})$ is the highest yet reported by CVD for ungated Si 2DEGs. Further, a Si 2DEG layer consists of isotopically-enriched $^{28}$Si to minimize spin decoherence due to $^{29}$Si. SIMS results show that in the Si 2DEG layer, $^{28}$Si is enriched from natural abundance of 92.2{\%} to 99.8{\%} with $^{29}$Si reduced from 4.7{\%} to an upper limit of $\sim $ 0.24{\%} and $^{30}$Si reduced from 3.1{\%} to $\sim $ 63ppm. Finally, effective Schottky gating requires a sharp turn-off slope in phosphorus from the doped layer to the surface for low electric fields near the surface. We have achieved ultra-sharp turn-off slope of $\sim $16 nm/dec, and demonstrate Schottky gating to fully deplete the 2DEG with extremely low leakage current.