> I would like to know if the p-doping of bulk Si could
> significatively change its
> Young modulus. I've heard, for instance, that the Young
> modulus could be of
> about 130GPa (instead of 170GPa) in the <100> direction but
> it seems to be a little bit exaggerated.
>
> Has anybody ever determined the Young modulus value for
> 10ohm*cm (p) doped Silicon?
> Liviu

Usually single-crystal silicon beams are fabricated in directions
parallel and perpendicular to the flat of a (100) wafer.
These are <110>-type directions, and Young's modulus is 169 GPa.
In the <100>-type directions, which are at 45-degree angles to the flat,
Young's modulus is 130 GPa.
This might account for what you've heard.

A good way of looking at Young's modulus is as a "spring constant" for
pulling the atoms in a crytal slightly apart or pushing them together.
A low amount of doping will not affect the bonding between the atoms.
A high doping (say 1e20 boron atom/cm^3 in a silicon crystal,
which has 5e22 atom/cm^3) is still less that 1% of the total
and should have only a small effect on Young's modulus.
In a review by A. George, "Elastic constants and moduli of diamond cubic Si/
Doping dependence of elastic constants," in the book "Properties of Crystalline
Silicon,"
edited by Robert Hull, IEE, 1999, p. 102, it says that the typical effect
of heavy doping is to decrease the elastic constants by 1-3%.

        --Kirt Williams Agilent Technologies