Effect of wave-function anisotropy on the metal-insulator transition density in many-valley semiconductors

It is shown that in the absence of central cell corrections, anisotropy of the donor envelope functions is the most important factor in determining the change in the metal-insulator transition density as a function of uniaxial stress in $n$-doped many-valley semiconductors. Quantitative agreement is obtained with experimental results for antimony-doped germanium, and a prediction made for the corresponding case in silicon.