Boron diffusion in extrinsically doped crystalline silicon

Boron diffusion is investigated in details by monitoring B-sharp concentration profiles embedded in isoconcentration doping backgrounds. Atomistic diffusion parameters (kick-out rate g, mean-free path of the mobile species λ, and the diffusivity D) are experimentally evaluated as a function of temperature and doping level both of p or n type. This allows for a quantitative determination of the physical phenomena involved in the B diffusion process. We found that negatively charged substitutional B diffuses by interaction with neutral or doubly positively charged self-interstitials. The BI complex formed after interaction diffuses mainly in a neutral state and, to a less extent, through singly negatively charged state. The former contributes for about one tenth to the full diffusion in intrinsic condition at 700 °C whereas it plays a significant role in high n-codoping regime. Moreover, n codoping with As or P induces a Coulomb pairing between the different charge states of the dopants that reduces diffusion. Pairing effect is disentangled by the effect of BI− diffusion and pairing energies are determined for both As and P presence. The resulting quantitative model of diffusion is presented and compared with existing literature.