On the charged-impurity-limited mobility for a very pure semiconductor

The low temperature mobility μ limited by charged impurities in very pure semiconductors (Ge) is interpreted in terms of the Coulomb collision in medium. The theory yields a peculiar dependence in temperature T and charged impurity concentration $\text{n}{}_{\mathrm{s}}\text{: μ ∞n}{}_{\mathrm{s}}{}^{\mathrm{<mtext>-</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$.