Enhanced dopant activation in heavily doped epitaxial silicon via sequential phosphorus–antimony co-doping

As silicon devices continue to scale, source–drain series resistance has become a critical limitation, which has motivated the development of heavily doped n-type silicon formed by in situ epitaxial doping. However, phosphorus, the most widely used n-type dopant, exhibits limited electrical activation at high concentrations due to the formation of phosphorus–vacancy complexes. In this work, we report the first experimental investigation of phosphorus–antimony (P–Sb) co-doping in epitaxial silicon grown by ultrahigh-vacuum chemical vapor deposition using a metal–organic antimony precursor. We show that simultaneous P–Sb co-doping is ineffective in the heavily doped regime, whereas a sequential co-doping strategy that introduces phosphorus during the initial growth stage followed by antimony effectively enhances dopant activation. The optimized sequentially co-doped film achieved a carrier concentration of 1.06 × 1020 cm−3, a Hall mobility of 71.25 cm2 V−1 s−1, and a conductivity of 1208 Ω−1 cm−1. The efficiency of the dopant activation evaluated using areal carrier and dopant densities from Hall-effect measurements and secondary ion mass spectrometry increased from 16.6% for phosphorus-only doping to 63.9% for sequential co-doping. Subsequent oxygen-ambient rapid thermal annealing suppressed phosphorus out-diffusion and reduced sheet resistance from 275 to 45.1 Ω/sq, among the lowest values reported for heavily doped n-type silicon. These results demonstrate that sequential P–Sb co-doping enabled by a metal–organic antimony precursor provides an effective and scalable approach to grow highly conductive n-type silicon epitaxial layers for advanced source–drain engineering.