An engineered metal-to-insulator transition in a two-dimensional network of degenerate phosphorus quantum dots in silicon

Phosphorus quantum dots (QDs) in silicon are a prominent candidate for semiconductor quantum computing based on donor spins. In this work, we report the formation of degenerate phosphorus QDs with a radius of 3 nm confined in a two-dimensional plane in silicon. A multilayer of SiO2/POx/SiO2 on Si substrate is first deposited by atomic layer deposition, which serves as the capping layer, doping source, and doping mask. Defective channels in the SiO2 doping mask layer are then created by random argon (Ar) ion implantation. Finally, phosphorus dopants from the doping source layer, driven by pulsed laser annealing, diffuse through the defective channels in SiO2 into Si substrate, forming phosphorus QDs confined in a two-dimensional (2D) plane near the Si surface. By reducing the Ar dose, we observe a sharp metal-to-insulator transition (MIT) in the resulting 2D electron system. Based on the MIT model for quantum dots, we find that each Ar ion implantation has a chance of only 6.4%–8.1% to create a phosphorus quantum dot.