Low resistivity, super-saturation phosphorus-in-silicon monolayer doping

We develop a super-saturation technique to extend the previously established doping density limit for ultra-high vacuum monolayer doping of silicon with phosphorus. Through an optimized sequence of PH₃ dosing and annealing of the silicon surface, we demonstrate a 2D free carrier density of n_s = (3.6 ± 0.1) × 10¹⁴ cm⁻², ∼50% higher than previously reported values. We perform extensive characterization of the dopant layer resistivity, including room temperature depth-dependent in situ four point probe measurements. The dopant layers remain conductive at less than 1 nm from the sample surface and importantly, surpass the semiconductor industry target for ultra-shallow junction scaling of $<900 Ω◻−1$ at a depth of 7 nm.