Resistance increase in small-area Si-doped Al—n-Si contacts

This paper describes the degradation process and its mechanism for Si-doped Al-n-Si contacts. A drastic resistance increase is observed in small-area contacts by subsequent heat treatment after metallization. This resistance increase appears in a smaller contact area at a shorter heat-treatment time. This mechanism can be explained in terms of solid-phase epitaxial growth (SPEG) of p-Si supplied from Si-doped Al metallization on the contact surface. The SPEG starts to take place from the contact-window periphery, and proceeds toward the contact-window center. Finally, the entire contact window is covered with the SPEG p-Si layer, and an additional p-n junction is formed in the original Al-n-Si contacts. With this p-n junction, the resistance increase is drastically caused. Activation energy for this phenomenon is about 1.3 eV, which is close to that for Si diffusion coefficient in bulk Al. This indicates that the SPEG is controlled by Si diffusion in Al and emphasizes that the resistance increase is caused by the SPEG.