Phonon Scattering by Neutral Donors in Germanium

Abstract

The excess thermal resistivity, ${w}_{\mathrm{ep}}$, produced in $n$-type Ge by neutral donors at temperatures below that of the maximum in thermal conductivity, has been measured for samples with P and Bi donor, and with samples with Ga and In acceptor compensation as well. If neutral-donor concentration, ${n}_{\mathrm{ex}}$, is low enough for the donor levels to be located in the gap, then ${w}_{\mathrm{ep}}$ decreases with increasing chemical shift $4{\ensuremath{\Delta}}_{c}$, as found earlier for As and Sb donors. In contrast to the insensitivity of ${w}_{\mathrm{ep}}$ to Ga or In compensation in Sb-doped $n$-Ge, Ga compensation strongly enhances ${w}_{\mathrm{ep}}$ in $n$-Ge doped with As or P. Electrical resistivity measurements agree with the attribution of this effect to modification of the core potential on compensation, the modification being stronger for larger $4{\ensuremath{\Delta}}_{c}$. For ${n}_{\mathrm{ex}}>5\ifmmode\times\else\texttimes\fi{}{10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the donor levels overlap the conduction band, and ${w}_{\mathrm{ep}}\ensuremath{\propto}{n}^{\frac{1}{3}}$ and is independent of impurity species or compensation.