Breaking the Doping Limit in Silicon by Deep Impurities

Increasing the free-carrier concentration in silicon is a pressing issue in modern electronics. The common shallow-level donors like P and As only permit electrically active doping up to 5×{}10²⁰ cm^-3. The authors discover that, surprisingly, doping with deep-level Te donors can actually exceed this limit. Density-functional calculations unveil the microscopic mechanism behind this behavior: Substitutional Te dimers occupying adjacent Si lattice sites provide free electrons. This work offers an alternative route to realizing the ultrahigh n-type doping required for Si-based next-generation electronics, as well as infrared optoelectronics.