Aluminium as a dopant atom in Silicon

[amit.31]

Hi all

What could be the reason for not using Aluminium as a dopant atom in Silicon, although it has also three valence electrons?

 

[erikl]

Al has a rather high diffusion coefficient in Si, so it is not well suited to create shallow diffusion regions (because of later often necessary thermal post-treatments). Even if one manages to create a shallow Al diffusion, its conductivity is less than that of a boron diffusion, because its energy state lies farther from the valence-band (57meV) than e.g. that of Boron (45meV), which means less of the Al atoms are ionized than Boron atoms. Altogether this means Al is not well suited as Si dopant in microelectronics.

In Power Electronics however, Al is often used as a fast Si dopant in order to create deep diffusion regions, which are needed for high conductivity (integrates over depth).