Phosphorus atomic layer doping in Ge using RPCVD

Abstract

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 ∼1.5×1014cm−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 Nt=1.55×1014cm−2 (a quarter of a monolayer), reaction rate constant kr=77s−1 and thermal equilibrium constant K=3.0×10−2Pa−1. An electrically active P concentration of 5–6×1019cm−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.