Effect of Internal Strains on Low Temperature Thermal Conductivity of Li Doped Ge

Abstract

In a previous paper (1), we determined the valley-orbit splitting 4Δ of Li donors in Ge from the measurement of the thermal conductivity K down to 0.4 K and its analysis. Here the measurement of K has been extended down to 0.06 K. The result shows that the ground state of Li donors has not a “normal” structure, but an “inverted” one, that is, the triplet lying below the singlet. The experimental data at T <0.3 K (see Fig. 1) cannot be explained only by scattering mechanisms considered in Ref. 1. In order to explain the lower temperature behaviour of K, we must take account of effects of random internal strains on the ground state and therefore on the donor-phonon interaction.