Enhanced Si–Ge interdiffusion in high phosphorus-doped germanium on silicon
Si–Ge interdiffusion with different P doping configurations was investigated. Significant interdiffusion happened when the Ge layers were doped with P in high 1018 cm−3 range, which resulted in a SiGe alloy region thicker than 150 nm after defect annealing cycles. With high P doped Ge, Si–Ge interdiffusivity is enhanced by 10–20 times in the xGe > 0.7 region compared with the control sample without P doping. We attribute this phenomenon to the much faster P transport towards the Ge seeding layers from the Ge side during the Ge layer growth, which increases the negatively charged vacancy concentrations and thus the interdiffusivity due to the Fermi effect in Si–Ge interdiffusion. This work is relevant to Ge-on-Si type device design, especially Ge-on-Si lasers.