Phosphorus atomic layer doping in Ge using RPCVD

Phosphorus atomic layer doping (P-ALD) in Ge is investigated at temperatures between 100°C and 400°C using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Hydrogen-terminated and hydrogen-free Ge (100) surfaces are exposed to PH₃ at different PH₃ partial pressures after interrupting Ge growth. The adsorption and reaction of PH₃ proceed on a hydrogen-free Ge surface. For all temperatures and PH₃ partial pressures used for the P-ALD, the P dose increased with increasing PH₃ exposure time and saturated. The saturation value of the incorporated P dose at 300°C is ∼1.5 × 10¹⁴ - cm^-3, which is close to a quarter of a monolayer of the Ge (100) surface. The P dose could be simulated assuming a Langmuir-type kinetics model with a saturation value of N_t = 1.55 × 10 ¹⁴cm^-2 (a quarter of a monolayer), reaction rate constant k_r = 77 s^-1 and thermal equilibrium constant K = 3.0 × 10^-2 Pa^-1. An electrically active P concentration of 5-6 × 10¹⁹ cm^-3, which is a 5-6 times higher thermal solubility of P in Ge, is obtained by multiple P spike fabrication using the P-ALD process.